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I have an 03 gs300 2JZ-GE VVTI. I just recently replaced the spark plugs, ignition coils, spark plug wires, aswell as the camshaft and crankshaft position sensors. After i had replaced the crankshaft sensor my codes for it had gone away without problem. Than i had gotten misfire codes so i replaced the spark plugs, still misfiring. Than ignition coils, still missfiring. Than wires, still misfiring. Yes, im aware injectors COULD be a problem i have new ones coming soon but when i had tested them they all worked fine. I than replaced my camshaft position sensor the other day, and when i tried to drive it i barely made it a block before it stalled out multiple times. What should have been a 1 minute drive took around 10 because i couldn't get the car to stay started. Once i got back home i read all the codes, ill summarize them here but if the specific codes would help ill gladly supply them. Ignition coil low circuit, camshaft position sensor low circuit, crankshaft position sensor low circuit, H02S bank 2 sensor 1 low circuit, and misfire codes. All the parts are brand new, and all of those "low circuit" codes seem to lead into the same section of the engine harness. Is there something im missing here? Ive checked every fuse, relay, and ground. Everything in that area is perfectly fine. The entire engine wire harness was also replaced 50k miles ago so i cant imagine something happened with the wires as it never once sat for mice or other creatures. I can provide any extra small details if needed but im seriously stumped. Any help is extremely appreciated!!!
What happens if you put the old camshaft position sensor back in? Sounds like you ended up having more issues after replacing that.
Id definitely love to try that but the metal part of the sensor broke off when i took the sensor out, so the old one is completely useless and i threw it away. I know low circuit could mean there's not the correct voltage going too the things ive listed but everything with my battery works perfectly. I do run subs and have an aftermarket pa system hooked to my battery but those problems were persistent before those things got hooked up.
Your engine harness is damaged in one or more places. Typically this occurs in the area across the cylinder head cover, spark plug valley, throttle body and injectors. Either broken or shorted. Can be difficult to find since everything is wrapped in a single harness. Also, when this happens, there is a risk of burning the outputs from the ECU and ignition control module. So after fixing the wiring problem, you may have to repair / replace these modules.
When the metal part of the sensor broke off, did you make sure there was absolutely nothing remaining of it inside the head? That could definitely cause some problems.
If you just replaced all these sensors and none of them are working, my first instinct is that something's wrong with your new sensors. Are they Lexus, or aftermarket? Aftermarket sensors genuinely can be bad right out of the gate.
Second instinct, and nobody else has said this, is your alternator. You're saying you're checking things like your battery, what're you using to check? Have you verified your alternator's working? I've seen so many times where a car comes in with like 90 codes, won't stay on, and it's literally just that the alternator isn't supplying enough power to keep everything alive. Could be one of your ground wires, as opposed to the cable that charges the battery. Sometimes the battery will still be getting a usable enough charge to not trip the battery light, but the alternator will still not be doing its job right, or the wires leading to the alternator will be the issue.
Like others have said, it could be your harness, as well, but since you replaced that recently, I'd rule out the alternator and the sensors themselves first.
Sorry you're dealing with this. Random electrical problems are never fun.
Lastly, if you disconnected the battery for long enough and then you suddenly had all these issues with sensors, this is a long shot but I've seen it happen; maybe it needs to go through the idle relearn? You did just kinda shift around where everything is and which sensors you're using, it's getting ever so slightly different readings than the computer is used to, and might need to be recalibrated to "find" everything again. Once again, far more likely if you're using aftermarket sensors, and seeing as the whole "idle relearn of death" thing that some Toyota's do is barely ever an issue on the GS, it might be better to just make sure those sensors are actually working properly before worrying about that.
Last edited by DanielleAlek; Apr 25, 2025 at 05:34 PM.
Reason: Idle relearn?
When the metal part of the sensor broke off, did you make sure there was absolutely nothing remaining of it inside the head? That could definitely cause some problems.
If you just replaced all these sensors and none of them are working, my first instinct is that something's wrong with your new sensors. Are they Lexus, or aftermarket? Aftermarket sensors genuinely can be bad right out of the gate.
Second instinct, and nobody else has said this, is your alternator. You're saying you're checking things like your battery, what're you using to check? Have you verified your alternator's working? I've seen so many times where a car comes in with like 90 codes, won't stay on, and it's literally just that the alternator isn't supplying enough power to keep everything alive. Could be one of your ground wires, as opposed to the cable that charges the battery. Sometimes the battery will still be getting a usable enough charge to not trip the battery light, but the alternator will still not be doing its job right, or the wires leading to the alternator will be the issue.
Like others have said, it could be your harness, as well, but since you replaced that recently, I'd rule out the alternator and the sensors themselves first.
Sorry you're dealing with this. Random electrical problems are never fun.
Lastly, if you disconnected the battery for long enough and then you suddenly had all these issues with sensors, this is a long shot but I've seen it happen; maybe it needs to go through the idle relearn? You did just kinda shift around where everything is and which sensors you're using, it's getting ever so slightly different readings than the computer is used to, and might need to be recalibrated to "find" everything again. Once again, far more likely if you're using aftermarket sensors, and seeing as the whole "idle relearn of death" thing that some Toyota's do is barely ever an issue on the GS, it might be better to just make sure those sensors are actually working properly before worrying about that.
What is a "idle relearn"? If it consists of letting the car idle that i might as well shoot myself in the foot because it wont idle for more than a few minutes at a time. Another thing i did forgot to point out is that my ignition coil plugs have their wires spliced to the stock harness. I bought new ones and they literally disappeared into the wind, like the wind blew them away. I was thinking about ordering new ones again but the pins and connections to the engine harness are all fine but could it maybe be something there? I also haven't tested the alternator and have no clue how to do it plus i don't think itd make it to my local autozone. My injectors will be coming tomorrow so maybe ill figure something out? Any further help would be awesome
Right now, you have a ton of variables that still haven't been ruled out by the presence of new parts. I'd say it's time to take a step back and return to the basics.
First off, what were you trying to fix when you initially started replacing things, what order did you replace them in, and how much time was there between each replacement? When did which codes appear in all of this process? It's hard to tell from your original post the actual timeline of events. It reads like you replaced everything twice.
The way I currently understand it is:
You had a misfire. You replaced spark plugs and wires, ignition coils, and the crank and cam position sensors, all at the same time. This didn't make your problem go away, so you proceeded to replace each of these things again, one at a time. When you replaced the camshaft position sensor, it immediately got worse, and continually stalled out. After that is when you started getting all of the low circuit codes.
Or
You had a crankshaft position sensor code. You replaced that, and THEN you had a misfire code, and after that is when you replaced all the ignition components, still had a misfire, and then you replaced the camshaft position sensor and that's when the problem got significantly worse, throwing you all those codes.
If the first scenario is the case, you should double check that those sensors are actually good, but you should be doing electrical diagnosis on the whole system. Buy a multimeter and start backprobing everything to check for extra resistance. If you can put the old camshaft position sensor back on and get the car to actually run, then backprobe with the car on to get voltages as well.
If the second scenario is the case, then it's a pretty open-and-shut case; your crankshaft position sensor is bad. The one you replaced it with has been the problem the whole time. An engine can run like this, but not well. It won't be able to be confident where the crankshaft is, and will be guessing based off of whatever data it IS getting from the crankshaft position sensor, along with clean data from the camshaft position sensor. Those things mixed together will give it juuuust enough info to get the ignition timing right, but not reliably.
Since we're talking about a direct-ignition engine, the timing belt only makes sure the valves open and close at the correct time. As far as the spark goes, that's entirely the ECU, so the ECU needs to have a perfect image of where the crank and cams are to do that job properly.
When you put in a camshaft position sensor from the same source, now your engine has literally no idea where anything is and no longer has any way to figure out ignition timing, which is why it won't run. The valves are opening and closing at the right time still since that's all mechanically driven, but the coils have absolutely no idea when to fire without getting reliable data on where the crank and cams are in their rotation.
Wherever you're getting your sensors from, they suck. Either that, or you didn't clean the mating surface properly before installing the new sensors. This is ESPECIALLY easy on the camshaft position sensor. Did you take the intake manifold plenum off before doing the camshaft sensor? It's really, really easy to accidentally end up with a dirty mating surface if you're trying to squeeze your hand behind it instead of removing it.
It's also important to make sure the sensors themselves are clean. They can easily pick up metal flakes while you're handling them, since they have magnets, if I recall correctly. The connectors can also be dirty, especially if they're taken from a junkyard car.
Last edited by DanielleAlek; Apr 25, 2025 at 11:49 PM.
Right now, you have a ton of variables that still haven't been ruled out by the presence of new parts. I'd say it's time to take a step back and return to the basics.
First off, what were you trying to fix when you initially started replacing things, what order did you replace them in, and how much time was there between each replacement? When did which codes appear in all of this process? It's hard to tell from your original post the actual timeline of events. It reads like you replaced everything twice.
The way I currently understand it is:
You had a misfire. You replaced spark plugs and wires, ignition coils, and the crank and cam position sensors, all at the same time. This didn't make your problem go away, so you proceeded to replace each of these things again, one at a time. When you replaced the camshaft position sensor, it immediately got worse, and continually stalled out. After that is when you started getting all of the low circuit codes.
Or
You had a crankshaft position sensor code. You replaced that, and THEN you had a misfire code, and after that is when you replaced all the ignition components, still had a misfire, and then you replaced the camshaft position sensor and that's when the problem got significantly worse, throwing you all those codes.
If the first scenario is the case, you should double check that those sensors are actually good, but you should be doing electrical diagnosis on the whole system. Buy a multimeter and start backprobing everything to check for extra resistance. If you can put the old camshaft position sensor back on and get the car to actually run, then backprobe with the car on to get voltages as well.
If the second scenario is the case, then it's a pretty open-and-shut case; your crankshaft position sensor is bad. The one you replaced it with has been the problem the whole time. An engine can run like this, but not well. It won't be able to be confident where the crankshaft is, and will be guessing based off of whatever data it IS getting from the crankshaft position sensor, along with clean data from the camshaft position sensor. Those things mixed together will give it juuuust enough info to get the ignition timing right, but not reliably.
Since we're talking about a direct-ignition engine, the timing belt only makes sure the valves open and close at the correct time. As far as the spark goes, that's entirely the ECU, so the ECU needs to have a perfect image of where the crank and cams are to do that job properly.
When you put in a camshaft position sensor from the same source, now your engine has literally no idea where anything is and no longer has any way to figure out ignition timing, which is why it won't run. The valves are opening and closing at the right time still since that's all mechanically driven, but the coils have absolutely no idea when to fire without getting reliable data on where the crank and cams are in their rotation.
Wherever you're getting your sensors from, they suck. Either that, or you didn't clean the mating surface properly before installing the new sensors. This is ESPECIALLY easy on the camshaft position sensor. Did you take the intake manifold plenum off before doing the camshaft sensor? It's really, really easy to accidentally end up with a dirty mating surface if you're trying to squeeze your hand behind it instead of removing it.
It's also important to make sure the sensors themselves are clean. They can easily pick up metal flakes while you're handling them, since they have magnets, if I recall correctly. The connectors can also be dirty, especially if they're taken from a junkyard car.
Here's the most recent update of events. I got the car about a month ago knowing it had a misfire and the ONLY code was for a misfire. I replaced the spark plugs the next day and the car ran fine for around 4 days. I noticed it misfiring again and when i checked the codes i had "camshaft position sensor low circuit", "ignition coil primary A low circuit", "crankshaft position sensor low circuit" codes. I went to orileys and bought both the camshaft and crankshaft sensors aswell as the ignition coils. I replaced the crankshaft position sensor that day, in the process i had to take the alternator off to access it which knocked one of the wires in the connector loose. I re-pinned it and thought itd be fine. I than replaced the ignition coils. I never ended up replacing the camshaft sensor because the code had gone away. I went about 2 days with no problems after that. Than i received a pending code for "multiple misfires detected", and a code for "ignition coil primary A low circuit". I do admit i drove it like that for about a week because i didn't have the money to get it checked at the time. Than after that week i noticed that it would occasionally sputter when around 3k rpms in mode 2 and 3 but not 4 or 5. Than after a few days of that it would randomly start running really rough and stall out, not any specific gap in time, just random. I figured injectors so i pulled my airbox, throttle body, and intake manifold to inspect/clean the injectors. All of my gaskets and O rings were perfectly fine and i cleaned my injectors with carb-cleaner and they all sprayed perfectly. I had put the injectors and everything together and tried to take it for a drive, i stalled out several times. At one point i had to crank it and rev to high rpm and drop it from neutral to drive to get into my driveway, transmission is a-okay. I found out that i had a fuel leak from the fuel rail because of a rolled over o-ring. When i removed the fuel rail i actually ended up breaking the nozzle off of one of them. I had my dad order me new ones. It sat from April 20th and is still currently sitting. Its been a solid 55-65F during the day and around 40F at night so its not deathly cold. I got my new injectors on the 26th and installed them, after the fact i had realized they were 1000cc injectors, where as stock is around 250cc i believe. I didn't quite think much of it at the time. I was able to get it started and running on its own but it would not rev past 3k rpm and was VERY choppy, on idle it sounded like an old hot rod. It also smoked up my entire front yard and garage, also didn't think much of it because from what i know sometimes injectors do that after being newly installed. I checked engine codes and found 7 low circuit codes. I immediately shut my car off and checked my alternator connector i had recently mentioned and the wires were ripped out. I ran up to orileys, purchased a new connector, and installed it making sure to reference the old connectors pattern ensuring i wired the cables correctly. Now when i try to start it, it takes exactly 15 seconds to start every single time. When it starts running without the starter i push the pedal and it hits around 3k rpm and immediately drops back down, if im lucky i can keep it running with my foot at about half throttle. Otherwise it will not stay started on its own. Im not sure if maybe its because its not getting enough fuel sent to it because of my over-size injectors, if thats the case i know some vehicles have a way to adjust the fuel pump for a higher psi output. My injectors require around 50-55 where stock fuel pump is 35-40. If thats a problem is there a way around buying a new pump? I've reached the end of my mechanical knowledge, this is the deepest ive ever been into anything fuel related. Or possibly even engine related. My biggest goal is to keep it away from shops because all the ones around me are money sharks and i need my car before may 10th so im hoping to figure this out asap.
Edit: i forgot to mention i had replaced the camshaft position sensor when i originally cleaned my injectors, i made sure to clean the port AND plug for the sensor.
Edit 2: It started and idled on it's own for 5-10 minutes until it died after i ran the pump about 10 times. During idle it was spitting out white smoke and it was very very rough. Im looking into vacuum lines today for the bad idle problem but that doesn't cover the white smoke. I checked for a bad head gasket too, no coolant or bubbles in the oil so thats not a concern. Im going to grab an OEM injector from AutoZone today and put the stock ones back in to see if its possibly the injectors aswell.
Last edited by Lexxy2JZ; Apr 27, 2025 at 03:28 AM.
First off, thanks for taking the time to write all that, it genuinely does help figure out what's going on.
If you want this figured out before May 10th, here's what I would do if this car came into my shop and I knew this history. This is gonna be a lot of information, and I'm gonna explain it like you're an amateur. I'm not trying to be condescending by doing that, I just wanna cover my bases and make sure everything is explained as thoroughly as I can.
I'd remove every aftermarket part and return whatever's still within the return period. That includes the fuel injectors. Then, I'd either order new or swipe from a junkyard original Lexus parts. You can get new Lexus parts here: www.lexuspartsnow.com/
Way cheaper than the dealership. You can also use car-part.com to see if there's any junkyards near you that have a car with a 2JZ in it, like a GS300, IS300, SC300, ect.
Sensors are resilient on these cars, so I wouldn't really be upset about getting them used. It's wear items, like o-rings, gaskets, hoses, timing belt components, ect. that you don't wanna be reusing. You might be able to get away with reusing some of your old parts, like the crankshaft position sensor and ignition coils, at least for diagnostic purposes. If you do this right, the car should start running like it did when you got it; poorly, but still usable.
The reason I'd do this is basically just to get the car back to its last known good state. I've heard those O'Reilly sensors can have failure rates as high as 35% out of the box, and you know that at least 85% of statistics on the internet are true. Every single time I've ever seen one used on a car, it's been a problem. They don't actually make sensors for these cars, what they do is they make general-purpose sensors and then package them in the same shell as the one that goes in our car. This works sometimes, but often times, you get a sensor that just isn't giving the signals the ECU is expecting, and you end up in this situation.
As for the fuel injectors, any time you're changing the size/capacity of your fuel injectors, you're gonna need to tune the car to match it. You're dumping a ton of fuel into the cylinders without adding more air, which drowns the engine and makes it stall out. To compensate, your ECU is gonna try to decrease the amount of fuel it's spraying into the cylinders, which decreases the fuel pressure, and since your injectors run at a higher pressure than stock, that means now you're not getting enough fuel, which makes the engine increase fuel pressure, which means now you're not getting enough air. It's a vicious cycle that basically ends in the car not running, exactly as you've seen. Unless you tune the engine to tell the ECU "Hey, this is actually running differently now, please compensate in this specific way", it'll be a problem.
When it comes to the alternator, a bad connection to the alternator means less efficient power delivery, which means your starter is gonna have to crank longer to achieve the same effect as if it had a good connection to the alternator. Even if it's just the ECU connection, the ECU might purposefully be running it in a low-power "safe state" because it can't see if the battery has a good voltage or not. I'm talking out of my *** on that last sentence, I have no idea if the 2JZ does that or not, but some cars do.
Test the components before reinstalling, though. Here's a video on how to test crankshaft and camshaft position sensors:
Below, I've shown the service manual pages that have the specs for these sensors.
Throw out whatever doesn't pass the test, reuse whatever does.
With all those variables out of the way, you can start to do diagnostics to find out what the original issue was.
When you're getting multiple related sensors throwing codes at once, there's three main options; wiring problems, the ECU is busted, or, the sensor is working as intended. Low circuit codes usually mean number 3 isn't true, that usually means that the computer is getting no signal, not an improper signal, but it's worth noting something important here.
One of the biggest mistakes I see inexperienced mechanics make is think that the codes are telling you what's broken on your car. It's not. The check engine light codes are telling you which sensor's signals are deviating from the norm. For example, if you have a crankshaft position sensor code, it's not saying "My crankshaft position sensor is broken", it's saying "Something is off about the signal I'm getting from the crankshaft." If you're getting both a crankshaft position code and a camshaft position code, your engine might be telling you "Hey, these signals don't like up. The camshaft and crankshaft aren't in sync!" That'll usually trip a timing code, as well, but not always. The first assumption you should make is to always run diagnostics on what the sensor is attached to, rather than blame the sensor.
In this instance, you're getting low circuit codes, which is usually the engine saying "I can't read the crankshaft position sensor data!", which usually does mean the sensor isn't working correctly. But, the same logic still applies; diagnose what the sensor is attached to before replacing it. In this instance, you're likely gonna be doing some electrical diagnosis, so this is where things get complicated (and possibly expensive).
Once it's back together with parts that I trust, I'd start some basic electrical system diagnostics, using a multimeter, and some test leads that have back probes.
First, the obvious, check your fuses and relays to make sure none of them are blown. Here's a video about how to test relays:
I always try to start electrical checks from the top down, instead of the other way around, just to rule out any system-wide issues as early as possible. Here's a document that has a lot of wiring information, what you're focusing on here for now is the first page that has the grounding points listed:
2jz.se/application/files/9914/3781/8915/ElectricalConnections.pdf
Now, it's time to backprobe the sensors that're giving us trouble. If you can get some backprobes into the alternator connector, the crankshaft sensor connector, the camshaft sensor connector, and the ignition coil connector, that should give you the info you need to know to move on. We're basically just looking to make sure we don't have any major electrical faults, here's a video on basic electrical diagnosis:
In case you get deep enough into this part of the diagnostics to need it, here's a post that has the ECU pinouts for these cars. That'd be for checking continuity, so you can backprobe the correct pin on the ECU to check for continuity in the entire wire. Remember that your car is gonna be using the 2001 GS300 ECU, not the 1998 GS300 ECU. You're definitely gonna want the battery unplugged for everything other than the voltage test, never plug in or unplug a connector with the battery plugged in. http://www.clublexus.com/forums/perf...-pinout-2.html
Usually, your reference signals are gonna be 12v or 5v. If you're seeing something like 4v or 11v, that might indicate an issue, but it's hard to tell for certain without an oscilloscope. Remember, those are the reference ground signals, not your active signal. You can't check your active signal using a multimeter.
This will also help to determine which of your connectors should be replaced. You mentioned earlier that some of your ignition coil connections were spliced, this is a good way to see how well those are holding up.
As for finding where the wiring fault is, uhh, that sucks lol the answer is either buy expensive equipment that can locate a wiring fault, or check by-hand. At that point, it can be easier to redo the entire wire than to track down where the break is.
You might've noticed that guy in the last video is using an oscilloscope, not just a multimeter. When checking reference signal voltage on sensors, you're usually gonna be using an oscilloscope, because it lets us actually see the signals being sent to and from the sensor in real-time, instead of having to guess based off of voltages. These sensors don't necessarily run at specific voltages, they send pulse width signals. You can only guess average voltage using a multimeter, oscilloscope tells you more about the quality of the overall signal. Here's a video going through the basics of those:
A signal that significantly deviates from the expected, even when the wire has proper continuity and isn't shorted, usually points to a bad ECU. Remember, by backprobing it, we're testing the connection to the sensor, not the sensor itself. We already tested the sensor itself when we checked the resistance between the sensor pins.
Now, say you do all of those tests and everything looks perfectly fine, and you can't find any issues. Honestly, this is the worst-case scenario for me, because now you could be dealing with what we call Electrical Gremlins, ex. "Mrs. Selvig's car was struck by lightning and now on the third Tuesday of every month, her check engine light beeps at her for exactly 0.25 seconds, but only when she's backing out of her driveway in 2nd gear and has her unlucky mug in the car with her".
Either that, or, we're back to square one; your sensors are absolutely fine. Nothing is wrong with your sensors, the codes are telling you to investigate what's attached to the sensors.
If this is the case, I'd be confused as to why you're getting low circuit codes and not, like, normal codes, but I have seen it happen before, so in case that happens in this scenario;
It's your timing. Crankshaft position + camshaft position codes at the same time with a good ECU and no electrical faults is almost always a timing issue. Hell, even if you find the electrical problem, I'd still check your timing just for the hell of it, since it's so easy on these engines. All you do is set the engine to top dead center using the timing marks on the crankshaft, remove the upper timing cover, and make sure the timing marks on the camshaft gears line up with the ones on the timing cover.
Here's the service manual guide on that:
Even if all of that is good, you could still have a timing issue. Loose timing belt letting things wobble a bit more than they should, VVT cam gear actuator not working right, any of those sorts of things. But then, we're getting into a timing job, and let's save that for later.
I know it was a lot, I basically just dumped a bunch of homework on your desk, but hopefully, this helps guide you on your way.
Let me know if you have any questions or other issues.
Last edited by DanielleAlek; Apr 27, 2025 at 04:13 PM.
Reason: Forgot hyperlinks suck on this site.
First off, thanks for taking the time to write all that, it genuinely does help figure out what's going on.
If you want this figured out before May 10th, here's what I would do if this car came into my shop and I knew this history. This is gonna be a lot of information, and I'm gonna explain it like you're an amateur. I'm not trying to be condescending by doing that, I just wanna cover my bases and make sure everything is explained as thoroughly as I can.
I'd remove every aftermarket part and return whatever's still within the return period. That includes the fuel injectors. Then, I'd either order new or swipe from a junkyard original Lexus parts. You can get new Lexus parts here: www.lexuspartsnow.com/
Way cheaper than the dealership. You can also use car-part.com to see if there's any junkyards near you that have a car with a 2JZ in it, like a GS300, IS300, SC300, ect.
Sensors are resilient on these cars, so I wouldn't really be upset about getting them used. It's wear items, like o-rings, gaskets, hoses, timing belt components, ect. that you don't wanna be reusing. You might be able to get away with reusing some of your old parts, like the crankshaft position sensor and ignition coils, at least for diagnostic purposes. If you do this right, the car should start running like it did when you got it; poorly, but still usable.
The reason I'd do this is basically just to get the car back to its last known good state. I've heard those O'Reilly sensors can have failure rates as high as 35% out of the box, and you know that at least 85% of statistics on the internet are true. Every single time I've ever seen one used on a car, it's been a problem. They don't actually make sensors for these cars, what they do is they make general-purpose sensors and then package them in the same shell as the one that goes in our car. This works sometimes, but often times, you get a sensor that just isn't giving the signals the ECU is expecting, and you end up in this situation.
As for the fuel injectors, any time you're changing the size/capacity of your fuel injectors, you're gonna need to tune the car to match it. You're dumping a ton of fuel into the cylinders without adding more air, which drowns the engine and makes it stall out. To compensate, your ECU is gonna try to decrease the amount of fuel it's spraying into the cylinders, which decreases the fuel pressure, and since your injectors run at a higher pressure than stock, that means now you're not getting enough fuel, which makes the engine increase fuel pressure, which means now you're not getting enough air. It's a vicious cycle that basically ends in the car not running, exactly as you've seen. Unless you tune the engine to tell the ECU "Hey, this is actually running differently now, please compensate in this specific way", it'll be a problem.
When it comes to the alternator, a bad connection to the alternator means less efficient power delivery, which means your starter is gonna have to crank longer to achieve the same effect as if it had a good connection to the alternator. Even if it's just the ECU connection, the ECU might purposefully be running it in a low-power "safe state" because it can't see if the battery has a good voltage or not. I'm talking out of my *** on that last sentence, I have no idea if the 2JZ does that or not, but some cars do.
Test the components before reinstalling, though. Here's a video on how to test crankshaft and camshaft position sensors:
Below, I've shown the service manual pages that have the specs for these sensors.
Throw out whatever doesn't pass the test, reuse whatever does.
With all those variables out of the way, you can start to do diagnostics to find out what the original issue was.
When you're getting multiple related sensors throwing codes at once, there's three main options; wiring problems, the ECU is busted, or, the sensor is working as intended. Low circuit codes usually mean number 3 isn't true, that usually means that the computer is getting no signal, not an improper signal, but it's worth noting something important here.
One of the biggest mistakes I see inexperienced mechanics make is think that the codes are telling you what's broken on your car. It's not. The check engine light codes are telling you which sensor's signals are deviating from the norm. For example, if you have a crankshaft position sensor code, it's not saying "My crankshaft position sensor is broken", it's saying "Something is off about the signal I'm getting from the crankshaft." If you're getting both a crankshaft position code and a camshaft position code, your engine might be telling you "Hey, these signals don't like up. The camshaft and crankshaft aren't in sync!" That'll usually trip a timing code, as well, but not always. The first assumption you should make is to always run diagnostics on what the sensor is attached to, rather than blame the sensor.
In this instance, you're getting low circuit codes, which is usually the engine saying "I can't read the crankshaft position sensor data!", which usually does mean the sensor isn't working correctly. But, the same logic still applies; diagnose what the sensor is attached to before replacing it. In this instance, you're likely gonna be doing some electrical diagnosis, so this is where things get complicated (and possibly expensive).
Once it's back together with parts that I trust, I'd start some basic electrical system diagnostics, using a multimeter, and some test leads that have back probes.
First, the obvious, check your fuses and relays to make sure none of them are blown. Here's a video about how to test relays:
I always try to start electrical checks from the top down, instead of the other way around, just to rule out any system-wide issues as early as possible. Here's a document that has a lot of wiring information, what you're focusing on here for now is the first page that has the grounding points listed:
2jz.se/application/files/9914/3781/8915/ElectricalConnections.pdf
Now, it's time to backprobe the sensors that're giving us trouble. If you can get some backprobes into the alternator connector, the crankshaft sensor connector, the camshaft sensor connector, and the ignition coil connector, that should give you the info you need to know to move on. We're basically just looking to make sure we don't have any major electrical faults, here's a video on basic electrical diagnosis:
In case you get deep enough into this part of the diagnostics to need it, here's a post that has the ECU pinouts for these cars. That'd be for checking continuity, so you can backprobe the correct pin on the ECU to check for continuity in the entire wire. Remember that your car is gonna be using the 2001 GS300 ECU, not the 1998 GS300 ECU. You're definitely gonna want the battery unplugged for everything other than the voltage test, never plug in or unplug a connector with the battery plugged in. http://www.clublexus.com/forums/perf...-pinout-2.html
Usually, your reference signals are gonna be 12v or 5v. If you're seeing something like 4v or 11v, that might indicate an issue, but it's hard to tell for certain without an oscilloscope. Remember, those are the reference ground signals, not your active signal. You can't check your active signal using a multimeter.
This will also help to determine which of your connectors should be replaced. You mentioned earlier that some of your ignition coil connections were spliced, this is a good way to see how well those are holding up.
As for finding where the wiring fault is, uhh, that sucks lol the answer is either buy expensive equipment that can locate a wiring fault, or check by-hand. At that point, it can be easier to redo the entire wire than to track down where the break is.
You might've noticed that guy in the last video is using an oscilloscope, not just a multimeter. When checking reference signal voltage on sensors, you're usually gonna be using an oscilloscope, because it lets us actually see the signals being sent to and from the sensor in real-time, instead of having to guess based off of voltages. These sensors don't necessarily run at specific voltages, they send pulse width signals. You can only guess average voltage using a multimeter, oscilloscope tells you more about the quality of the overall signal. Here's a video going through the basics of those:
A signal that significantly deviates from the expected, even when the wire has proper continuity and isn't shorted, usually points to a bad ECU. Remember, by backprobing it, we're testing the connection to the sensor, not the sensor itself. We already tested the sensor itself when we checked the resistance between the sensor pins.
Now, say you do all of those tests and everything looks perfectly fine, and you can't find any issues. Honestly, this is the worst-case scenario for me, because now you could be dealing with what we call Electrical Gremlins, ex. "Mrs. Selvig's car was struck by lightning and now on the third Tuesday of every month, her check engine light beeps at her for exactly 0.25 seconds, but only when she's backing out of her driveway in 2nd gear and has her unlucky mug in the car with her".
Either that, or, we're back to square one; your sensors are absolutely fine. Nothing is wrong with your sensors, the codes are telling you to investigate what's attached to the sensors.
If this is the case, I'd be confused as to why you're getting low circuit codes and not, like, normal codes, but I have seen it happen before, so in case that happens in this scenario;
It's your timing. Crankshaft position + camshaft position codes at the same time with a good ECU and no electrical faults is almost always a timing issue. Hell, even if you find the electrical problem, I'd still check your timing just for the hell of it, since it's so easy on these engines. All you do is set the engine to top dead center using the timing marks on the crankshaft, remove the upper timing cover, and make sure the timing marks on the camshaft gears line up with the ones on the timing cover.
Here's the service manual guide on that:
Even if all of that is good, you could still have a timing issue. Loose timing belt letting things wobble a bit more than they should, VVT cam gear actuator not working right, any of those sorts of things. But then, we're getting into a timing job, and let's save that for later.
I know it was a lot, I basically just dumped a bunch of homework on your desk, but hopefully, this helps guide you on your way.
Let me know if you have any questions or other issues.
So i skimmed over this and honestly im extremely thankful for the info. Heres the updated situation on my car to see if we can maybe narrow it down a bit. I reinstalled the old fuel injectors, one of them has a broken pinto cap but from reading up that shouldn't effect anything (it hasn't made any noticable differences). The car DOES run and drive but not well. For example, i was getting on the freeway yesterday and it quite literally just cut ignition, im guessing spark because if i slammed the pedal to the floor it tried to start up again. But it basically just cut off randomly without warning. After that i went to start it and it started perfectly right away, the problem was that if i didn't immediately touch the gas it would die. It started like a normal car but instead of settling down at around 800ish rpm to idle it dropped down and died. I eventually got it going and for about the first 5 minutes of driving it would randomly continue to cut ignition, my best attempt at describing what happened was i had cruise control on going about 80mph and all of a sudden rpm dropped down to 0 and immediately back up to the proper rpm causing the car to almost lurch in a way. It stopped after about 5-10 minutes of driving. Once i got off the freeway i had to stop at a stop sign and noticed it would drop to around 2-300 rpm and was struggling to stay alive without gas, but it drove perfectly when accelerating. Later in the day i was driving it in "manual mode" with the button shifters and i noticed it almost stutters at higher rpm, it almost sounds like rolling anti-lag. Basically just stopping the rpm while still climbing if that makes sense. The rest of the day it only stuttered at higher rpm and i had to switch to neutral to hold it at 900rpm for it to stay alive at stoplights otherwise it would stall out. It also stalled out twice and just refused to start unless i held the gas and put it from neutral to drive.
This is probably bittersweet to hear, but it sounds like we're in the right direction. Getting new fuel injectors and starting the diagnosis of the sensors/electrical system seems to be the next step, imo.
Pintle caps aren't entirely necessary, but my general approach on cars is that everything is so complicated that changing any one variable could have unforeseen effects that you might not realize until later. For example, the pintle cap holds one of the o-rings for the fuel injectors in place. Either you're missing an o-ring, or you're, y'know, missing an o-ring. That o-ring could be in your garage, or it could be in your intake manifold, or worse yet, stuck between one of your valves and the seats. If it's just in your garage, you could possibly have created a leak, which can make the fuel delivery much more unpredictable.
If you just wanna try buying new pintle caps and o-rings, that could work out instead of having to buy a whole new injector.
Your sensors could also cause similar issues. If the computer loses track of where the crank and cam shafts are, it might go into a safe mode or cut out entirely to avoid damaging the engine. It doesn't want to end up slamming your pistons into your valves, after all. Also, it could still be running, but your tachometer will read 0 because it has no idea where the crankshaft actually is.
Your electrical system can cause these issues, too. I'm pretty sure both the fuel injectors and spark plugs run off of the alternator, since it's a fuel-injection engine with no mechanical distributor. If you have a sudden loss of electrical power, it'll result in the engine cutting out. This could be a system-wide failure, such as if the connection to the alternator is lost, or it could be a short in the wiring loom for the ignition system, or any other number of things. That's why I say it's worth doing at least basic electrical diagnosis, just to narrow the problem down more.
We could have a secret third issue that we won't know until we get all the other stuff figured/ruled out.
Low idle can be explained similarly with these things. It's difficult to know until we rule a few more things out, but at least now we know my theory on the fuel injectors was right. A big step in the right direction!
This is probably bittersweet to hear, but it sounds like we're in the right direction. Getting new fuel injectors and starting the diagnosis of the sensors/electrical system seems to be the next step, imo.
Pintle caps aren't entirely necessary, but my general approach on cars is that everything is so complicated that changing any one variable could have unforeseen effects that you might not realize until later. For example, the pintle cap holds one of the o-rings for the fuel injectors in place. Either you're missing an o-ring, or you're, y'know, missing an o-ring. That o-ring could be in your garage, or it could be in your intake manifold, or worse yet, stuck between one of your valves and the seats. If it's just in your garage, you could possibly have created a leak, which can make the fuel delivery much more unpredictable.
If you just wanna try buying new pintle caps and o-rings, that could work out instead of having to buy a whole new injector.
Your sensors could also cause similar issues. If the computer loses track of where the crank and cam shafts are, it might go into a safe mode or cut out entirely to avoid damaging the engine. It doesn't want to end up slamming your pistons into your valves, after all. Also, it could still be running, but your tachometer will read 0 because it has no idea where the crankshaft actually is.
Your electrical system can cause these issues, too. I'm pretty sure both the fuel injectors and spark plugs run off of the alternator, since it's a fuel-injection engine with no mechanical distributor. If you have a sudden loss of electrical power, it'll result in the engine cutting out. This could be a system-wide failure, such as if the connection to the alternator is lost, or it could be a short in the wiring loom for the ignition system, or any other number of things. That's why I say it's worth doing at least basic electrical diagnosis, just to narrow the problem down more.
We could have a secret third issue that we won't know until we get all the other stuff figured/ruled out.
Low idle can be explained similarly with these things. It's difficult to know until we rule a few more things out, but at least now we know my theory on the fuel injectors was right. A big step in the right direction!
Im going to invest in the electrical tools to test all the things you told me to try to get to the bottom of this. Youve been an amazing helper and i really really appreciate every bit youve told me. Im gonna hopefully get this all done within the next week or so, i usually blast through mechanical work on my car pretty quick. I worked on it 24 hours straight to get to the conclusion of the no start problem. Im going to come back to this thread with any updates that i have because your the first person to give me this much help.
This is probably bittersweet to hear, but it sounds like we're in the right direction. Getting new fuel injectors and starting the diagnosis of the sensors/electrical system seems to be the next step, imo.
Pintle caps aren't entirely necessary, but my general approach on cars is that everything is so complicated that changing any one variable could have unforeseen effects that you might not realize until later. For example, the pintle cap holds one of the o-rings for the fuel injectors in place. Either you're missing an o-ring, or you're, y'know, missing an o-ring. That o-ring could be in your garage, or it could be in your intake manifold, or worse yet, stuck between one of your valves and the seats. If it's just in your garage, you could possibly have created a leak, which can make the fuel delivery much more unpredictable.
If you just wanna try buying new pintle caps and o-rings, that could work out instead of having to buy a whole new injector.
Your sensors could also cause similar issues. If the computer loses track of where the crank and cam shafts are, it might go into a safe mode or cut out entirely to avoid damaging the engine. It doesn't want to end up slamming your pistons into your valves, after all. Also, it could still be running, but your tachometer will read 0 because it has no idea where the crankshaft actually is.
Your electrical system can cause these issues, too. I'm pretty sure both the fuel injectors and spark plugs run off of the alternator, since it's a fuel-injection engine with no mechanical distributor. If you have a sudden loss of electrical power, it'll result in the engine cutting out. This could be a system-wide failure, such as if the connection to the alternator is lost, or it could be a short in the wiring loom for the ignition system, or any other number of things. That's why I say it's worth doing at least basic electrical diagnosis, just to narrow the problem down more.
We could have a secret third issue that we won't know until we get all the other stuff figured/ruled out.
Low idle can be explained similarly with these things. It's difficult to know until we rule a few more things out, but at least now we know my theory on the fuel injectors was right. A big step in the right direction!
Heres an update on my current engine codes. P0301 Cylinder 1 Misfire detected, P0051 H02S Heater Control Circuit Low Bank 2 Sensor 1, P0113 Intake Air Temperature Sensor 1 Circuit High, P0154 O2 Sensor No activity detected bank 2 sensor 1, P0335 Crankshaft position sensor A Circuit, P0341 Camshaft position sensor A Circuit Range/Performance Bank 1 or single Sensor, P0351 Ignition Coil A primary/Secondary circuit.
Heres an update on my current engine codes. P0301 Cylinder 1 Misfire detected, P0051 H02S Heater Control Circuit Low Bank 2 Sensor 1, P0113 Intake Air Temperature Sensor 1 Circuit High, P0154 O2 Sensor No activity detected bank 2 sensor 1, P0335 Crankshaft position sensor A Circuit, P0341 Camshaft position sensor A Circuit Range/Performance Bank 1 or single Sensor, P0351 Ignition Coil A primary/Secondary circuit.
Electrical problems with wiring harnesses and connectors.
First off, thanks for taking the time to write all that, it genuinely does help figure out what's going on.
If you want this figured out before May 10th, here's what I would do if this car came into my shop and I knew this history. This is gonna be a lot of information, and I'm gonna explain it like you're an amateur. I'm not trying to be condescending by doing that, I just wanna cover my bases and make sure everything is explained as thoroughly as I can.
I'd remove every aftermarket part and return whatever's still within the return period. That includes the fuel injectors. Then, I'd either order new or swipe from a junkyard original Lexus parts. You can get new Lexus parts here: www.lexuspartsnow.com/
Way cheaper than the dealership. You can also use car-part.com to see if there's any junkyards near you that have a car with a 2JZ in it, like a GS300, IS300, SC300, ect.
Sensors are resilient on these cars, so I wouldn't really be upset about getting them used. It's wear items, like o-rings, gaskets, hoses, timing belt components, ect. that you don't wanna be reusing. You might be able to get away with reusing some of your old parts, like the crankshaft position sensor and ignition coils, at least for diagnostic purposes. If you do this right, the car should start running like it did when you got it; poorly, but still usable.
The reason I'd do this is basically just to get the car back to its last known good state. I've heard those O'Reilly sensors can have failure rates as high as 35% out of the box, and you know that at least 85% of statistics on the internet are true. Every single time I've ever seen one used on a car, it's been a problem. They don't actually make sensors for these cars, what they do is they make general-purpose sensors and then package them in the same shell as the one that goes in our car. This works sometimes, but often times, you get a sensor that just isn't giving the signals the ECU is expecting, and you end up in this situation.
As for the fuel injectors, any time you're changing the size/capacity of your fuel injectors, you're gonna need to tune the car to match it. You're dumping a ton of fuel into the cylinders without adding more air, which drowns the engine and makes it stall out. To compensate, your ECU is gonna try to decrease the amount of fuel it's spraying into the cylinders, which decreases the fuel pressure, and since your injectors run at a higher pressure than stock, that means now you're not getting enough fuel, which makes the engine increase fuel pressure, which means now you're not getting enough air. It's a vicious cycle that basically ends in the car not running, exactly as you've seen. Unless you tune the engine to tell the ECU "Hey, this is actually running differently now, please compensate in this specific way", it'll be a problem.
When it comes to the alternator, a bad connection to the alternator means less efficient power delivery, which means your starter is gonna have to crank longer to achieve the same effect as if it had a good connection to the alternator. Even if it's just the ECU connection, the ECU might purposefully be running it in a low-power "safe state" because it can't see if the battery has a good voltage or not. I'm talking out of my *** on that last sentence, I have no idea if the 2JZ does that or not, but some cars do.
Test the components before reinstalling, though. Here's a video on how to test crankshaft and camshaft position sensors:
Below, I've shown the service manual pages that have the specs for these sensors.
Throw out whatever doesn't pass the test, reuse whatever does.
With all those variables out of the way, you can start to do diagnostics to find out what the original issue was.
When you're getting multiple related sensors throwing codes at once, there's three main options; wiring problems, the ECU is busted, or, the sensor is working as intended. Low circuit codes usually mean number 3 isn't true, that usually means that the computer is getting no signal, not an improper signal, but it's worth noting something important here.
One of the biggest mistakes I see inexperienced mechanics make is think that the codes are telling you what's broken on your car. It's not. The check engine light codes are telling you which sensor's signals are deviating from the norm. For example, if you have a crankshaft position sensor code, it's not saying "My crankshaft position sensor is broken", it's saying "Something is off about the signal I'm getting from the crankshaft." If you're getting both a crankshaft position code and a camshaft position code, your engine might be telling you "Hey, these signals don't like up. The camshaft and crankshaft aren't in sync!" That'll usually trip a timing code, as well, but not always. The first assumption you should make is to always run diagnostics on what the sensor is attached to, rather than blame the sensor.
In this instance, you're getting low circuit codes, which is usually the engine saying "I can't read the crankshaft position sensor data!", which usually does mean the sensor isn't working correctly. But, the same logic still applies; diagnose what the sensor is attached to before replacing it. In this instance, you're likely gonna be doing some electrical diagnosis, so this is where things get complicated (and possibly expensive).
Once it's back together with parts that I trust, I'd start some basic electrical system diagnostics, using a multimeter, and some test leads that have back probes.
First, the obvious, check your fuses and relays to make sure none of them are blown. Here's a video about how to test relays:
I always try to start electrical checks from the top down, instead of the other way around, just to rule out any system-wide issues as early as possible. Here's a document that has a lot of wiring information, what you're focusing on here for now is the first page that has the grounding points listed:
2jz.se/application/files/9914/3781/8915/ElectricalConnections.pdf
Now, it's time to backprobe the sensors that're giving us trouble. If you can get some backprobes into the alternator connector, the crankshaft sensor connector, the camshaft sensor connector, and the ignition coil connector, that should give you the info you need to know to move on. We're basically just looking to make sure we don't have any major electrical faults, here's a video on basic electrical diagnosis:
In case you get deep enough into this part of the diagnostics to need it, here's a post that has the ECU pinouts for these cars. That'd be for checking continuity, so you can backprobe the correct pin on the ECU to check for continuity in the entire wire. Remember that your car is gonna be using the 2001 GS300 ECU, not the 1998 GS300 ECU. You're definitely gonna want the battery unplugged for everything other than the voltage test, never plug in or unplug a connector with the battery plugged in. http://www.clublexus.com/forums/perf...-pinout-2.html
Usually, your reference signals are gonna be 12v or 5v. If you're seeing something like 4v or 11v, that might indicate an issue, but it's hard to tell for certain without an oscilloscope. Remember, those are the reference ground signals, not your active signal. You can't check your active signal using a multimeter.
This will also help to determine which of your connectors should be replaced. You mentioned earlier that some of your ignition coil connections were spliced, this is a good way to see how well those are holding up.
As for finding where the wiring fault is, uhh, that sucks lol the answer is either buy expensive equipment that can locate a wiring fault, or check by-hand. At that point, it can be easier to redo the entire wire than to track down where the break is.
You might've noticed that guy in the last video is using an oscilloscope, not just a multimeter. When checking reference signal voltage on sensors, you're usually gonna be using an oscilloscope, because it lets us actually see the signals being sent to and from the sensor in real-time, instead of having to guess based off of voltages. These sensors don't necessarily run at specific voltages, they send pulse width signals. You can only guess average voltage using a multimeter, oscilloscope tells you more about the quality of the overall signal. Here's a video going through the basics of those:
A signal that significantly deviates from the expected, even when the wire has proper continuity and isn't shorted, usually points to a bad ECU. Remember, by backprobing it, we're testing the connection to the sensor, not the sensor itself. We already tested the sensor itself when we checked the resistance between the sensor pins.
Now, say you do all of those tests and everything looks perfectly fine, and you can't find any issues. Honestly, this is the worst-case scenario for me, because now you could be dealing with what we call Electrical Gremlins, ex. "Mrs. Selvig's car was struck by lightning and now on the third Tuesday of every month, her check engine light beeps at her for exactly 0.25 seconds, but only when she's backing out of her driveway in 2nd gear and has her unlucky mug in the car with her".
Either that, or, we're back to square one; your sensors are absolutely fine. Nothing is wrong with your sensors, the codes are telling you to investigate what's attached to the sensors.
If this is the case, I'd be confused as to why you're getting low circuit codes and not, like, normal codes, but I have seen it happen before, so in case that happens in this scenario;
It's your timing. Crankshaft position + camshaft position codes at the same time with a good ECU and no electrical faults is almost always a timing issue. Hell, even if you find the electrical problem, I'd still check your timing just for the hell of it, since it's so easy on these engines. All you do is set the engine to top dead center using the timing marks on the crankshaft, remove the upper timing cover, and make sure the timing marks on the camshaft gears line up with the ones on the timing cover.
Here's the service manual guide on that:
Even if all of that is good, you could still have a timing issue. Loose timing belt letting things wobble a bit more than they should, VVT cam gear actuator not working right, any of those sorts of things. But then, we're getting into a timing job, and let's save that for later.
I know it was a lot, I basically just dumped a bunch of homework on your desk, but hopefully, this helps guide you on your way.
Let me know if you have any questions or other issues.
Here's an update for ya. I did quite literally everything you said in this post over the last few weeks and not one thing fixed it. I actually was driving perfectly fine on the highway and when i got off the freeway it stalled out and just wouldn't start again so my best guess is that it got knocked out of timing but i had to bite the bullet and take it into the shop to get it looked at. I even went as far as ripping the head off and replacing the head gasket incase it was just a few cylinders with low compression and afterwards it still did it. I only had a Misfire code for cylinder 1 and 3 and an O2 sensor code for bank 2 sensor 1, which i bought the sensor not realizing i would have to quite literally remove the entire exhaust system in order to get to it.
Low circuit codes
