CEL code b2798
04-23-16, 02:03 PM
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CEL code b2798
Hey guys I'm new to owning a Lexus, and I'm pretty mechanically inclined but this one has me stumped. Purchased this rx300 awd off a friend of mine last week and I plan to fix it and drive it daily. So far no luck.
What its doing: it will start sometimes, and other times it will sit there and crank. when you rev it in park, it goes to 3k rpm and hit the rev limmiter. In drive, acts like transmission is in some kind of limp mode.
CEL throws codes for all 6 cylinders misfiring, even though at idle it runs flawless with no hesitation. Also throws a code (b2798) Communication Malfunction No. 2 Immobilizer System
I don't know much about the history of the vehicle, but what I do know is that it had a remote start installed on it at one time. The guy took it to a local shop and had them remove it when it started acting funny. So I decided to look under the dash and see if there was anything visually wrong with the ignition wires. Low and behold, there were wires that were hacked up and choppy coming out of one of the main plugs for the ignition. This rendered that plug useless where they had cut so close to the plug leaving me with no extra wire to work with. So I ended up finding a replacement plug off of one of our Toyota doner front ends sitting at work (I work in a body shop) and I was able to replace and re solder everything back together. After doing so, I hooked the battery back up and tested it, and still having the same issue.
I'm assuming that I've either got a bad key, or a bad ecm. Not sure what else could be faulty in between there. Before I go throwing parts at this, id like to figure out some sort of tests I can do with a DVOM to track down what's causing this. I can post pics of what kind of mess I had to clean up under the dash later this week. Any input on this subject would be greatly appreciated! Thanks guys.
What its doing: it will start sometimes, and other times it will sit there and crank. when you rev it in park, it goes to 3k rpm and hit the rev limmiter. In drive, acts like transmission is in some kind of limp mode.
CEL throws codes for all 6 cylinders misfiring, even though at idle it runs flawless with no hesitation. Also throws a code (b2798) Communication Malfunction No. 2 Immobilizer System
I don't know much about the history of the vehicle, but what I do know is that it had a remote start installed on it at one time. The guy took it to a local shop and had them remove it when it started acting funny. So I decided to look under the dash and see if there was anything visually wrong with the ignition wires. Low and behold, there were wires that were hacked up and choppy coming out of one of the main plugs for the ignition. This rendered that plug useless where they had cut so close to the plug leaving me with no extra wire to work with. So I ended up finding a replacement plug off of one of our Toyota doner front ends sitting at work (I work in a body shop) and I was able to replace and re solder everything back together. After doing so, I hooked the battery back up and tested it, and still having the same issue.
I'm assuming that I've either got a bad key, or a bad ecm. Not sure what else could be faulty in between there. Before I go throwing parts at this, id like to figure out some sort of tests I can do with a DVOM to track down what's causing this. I can post pics of what kind of mess I had to clean up under the dash later this week. Any input on this subject would be greatly appreciated! Thanks guys.
04-24-16, 06:28 PM
#2
Moderator
Welcome to CL.
Give it a few days for folks to see.
Your problems are not the common ones and worst may have been induced by reckless individual.
Salim
Give it a few days for folks to see.
Your problems are not the common ones and worst may have been induced by reckless individual.
Salim
04-25-16, 03:19 PM
#3
Driver School Candidate
The whole after-market remote start hack job and immobilizer error code have me a little concerned about the ECU. If the transponder on the key wasn't working you shouldn't be able to start the car. The fact that the engine idles fine makes me think the ECU is doing OK. Doing a quick Google search on the B2798 found a factory PDF which details how to diagnose either the transponder amplifier or the key. I would definitely start there as it involves measuring continuity between the two connectors (Transponder Key ECU Assy and Transponder Key Amplifier) and connector to ground. This will find any wiring issues.
Assuming you have gotten past the potential electrical issues, I would move on to mechanical issues with the sensors on the engine. The engine works like this: Air in through MAF (mass airflow sensor), air/gas mix and ignited in cylinder. Exhaust output FIRST measured by A/F sensors (air/fuel sensor), one on each bank located in the exhaust manifold. Manifolds come together under car and the final sensor, O2 sensor, measures exhaust for proper level.
The computer calculates from the MAF sensor on the intake to the A/F sensor(s) on each bank in order to adjust the timing of each bank of cylinders. It does this by sending electrical pulses to the OCV valves for each bank (oil control valves) which either allow or block the flow of oil pushing against a lobe on the upper camshaft for that bank. This can advance or retard the timing of that bank (1,3,5 or 2,4,6) as needed. The OCVs do not have monitoring capability by the ECU (engine control unit) so if one of both of them goes bad the ECU starts throwing codes for the sensors on either side of it (usually the A/F and O2 sensors).
Getting error codes for all 6 cylinders misfiring makes it a little harder to diagnose since you can't swap parts around to see if the problem moves banks. When I got the codes for cylinder 1 misfire then eventually a 2nd code for 1,3,5 bank misfiring I immediately swapped the coil packs on the two banks and reset the computer. Within 10 minutes the codes were back on the SAME bank. This told me the coils weren't the problem (no way all 6 coils go bad at once and if one was bad it would have thrown a code on the other bank when I swapped it). I forget how I checked the MAF sensor but it had been replaced a few years earlier so I highly doubted it as the problem. I then changed the A/F sensor for that bank and the O2 sensor under the car, cleared the codes, and checked it. Yep, codes came back. I then messed with the IACV on the intake, deciding to clean everything out. Yeah, this was a total grasping-at-straws moment as I was out of ideas (it definitely wasn't this as the problem!). I did manage to change the IACV setting by accidentally spinning the magnet on its shaft which caused the hit-the-rev-limit at startup then stall or by adjusting it too far the other way, now-the-engine-won't crank scenario. The fact that your car does idle once running tells me it's not this piece so don't mess with it!
Each time the car went into limp mode when the entire bank misfire code tripped. Resetting the codes via the OBDII port after each part swap/replace cleared the limp condition.
Finally I discovered the OCV issue (I didn't know about this part at the time) and changed out both of them. Only the rear bank one was bad but I did both for good measure. Problem solved! Changing all the sensors and OCVs I listed will MOST LIKELY solve your issue at this point, although it is the most expensive way to do it (guessing ~$500 US). You can try them piece-meal to see if you can get it solved otherwise. I would start with the two A/F sensors, the OCV valves, the MAF sensor and then the O2 sensor, in that order. What exact error codes are you getting?
Assuming you have gotten past the potential electrical issues, I would move on to mechanical issues with the sensors on the engine. The engine works like this: Air in through MAF (mass airflow sensor), air/gas mix and ignited in cylinder. Exhaust output FIRST measured by A/F sensors (air/fuel sensor), one on each bank located in the exhaust manifold. Manifolds come together under car and the final sensor, O2 sensor, measures exhaust for proper level.
The computer calculates from the MAF sensor on the intake to the A/F sensor(s) on each bank in order to adjust the timing of each bank of cylinders. It does this by sending electrical pulses to the OCV valves for each bank (oil control valves) which either allow or block the flow of oil pushing against a lobe on the upper camshaft for that bank. This can advance or retard the timing of that bank (1,3,5 or 2,4,6) as needed. The OCVs do not have monitoring capability by the ECU (engine control unit) so if one of both of them goes bad the ECU starts throwing codes for the sensors on either side of it (usually the A/F and O2 sensors).
Getting error codes for all 6 cylinders misfiring makes it a little harder to diagnose since you can't swap parts around to see if the problem moves banks. When I got the codes for cylinder 1 misfire then eventually a 2nd code for 1,3,5 bank misfiring I immediately swapped the coil packs on the two banks and reset the computer. Within 10 minutes the codes were back on the SAME bank. This told me the coils weren't the problem (no way all 6 coils go bad at once and if one was bad it would have thrown a code on the other bank when I swapped it). I forget how I checked the MAF sensor but it had been replaced a few years earlier so I highly doubted it as the problem. I then changed the A/F sensor for that bank and the O2 sensor under the car, cleared the codes, and checked it. Yep, codes came back. I then messed with the IACV on the intake, deciding to clean everything out. Yeah, this was a total grasping-at-straws moment as I was out of ideas (it definitely wasn't this as the problem!). I did manage to change the IACV setting by accidentally spinning the magnet on its shaft which caused the hit-the-rev-limit at startup then stall or by adjusting it too far the other way, now-the-engine-won't crank scenario. The fact that your car does idle once running tells me it's not this piece so don't mess with it!
Each time the car went into limp mode when the entire bank misfire code tripped. Resetting the codes via the OBDII port after each part swap/replace cleared the limp condition.
Finally I discovered the OCV issue (I didn't know about this part at the time) and changed out both of them. Only the rear bank one was bad but I did both for good measure. Problem solved! Changing all the sensors and OCVs I listed will MOST LIKELY solve your issue at this point, although it is the most expensive way to do it (guessing ~$500 US). You can try them piece-meal to see if you can get it solved otherwise. I would start with the two A/F sensors, the OCV valves, the MAF sensor and then the O2 sensor, in that order. What exact error codes are you getting?
Last edited by cotis; 04-25-16 at 03:42 PM.
06-12-16, 10:25 AM
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Sorry if it seems like I abandoned ship on this post. Been very busy and couldn't find much time to work on this thing until the other day. So far I've been able to rule out some stuff with my scan took after doing a bunch of research on sensors, and how they all communicate. I actually went as far as taking the intake off and replacing the harness for my knock sensors because I was so sure that was my issue. Turns out I was wrong. My scan tool shows that the timing is being automatically adjusted up and down in degrees as the engine idles, which tells me those knock sensors are functioning properly. I pulled both OCV sensors out and disassembled them, and cleaned them after reading about it on here. I also cleaned the little filters on each side of the engine close to the OCVs. Still have no luck. The codes that my scanner gives me are the following:
P0300
P1300
P1305
P1310
P1315
P1320
P1325
0300 is multiple random misfire detected
The rest of the codes are igniter circuit 1-6.
The car is able to start and run without hesitation, but it's definitely stuck in limp mode. And I just don't know what is keeping it in limp mode. I've even removed the ecm and taken it apart and visually inspected the board and it looks normal with no damage. I appreciate everyone's input on this issue!
P0300
P1300
P1305
P1310
P1315
P1320
P1325
0300 is multiple random misfire detected
The rest of the codes are igniter circuit 1-6.
The car is able to start and run without hesitation, but it's definitely stuck in limp mode. And I just don't know what is keeping it in limp mode. I've even removed the ecm and taken it apart and visually inspected the board and it looks normal with no damage. I appreciate everyone's input on this issue!
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