Hello to all,

Long time listener first time caller.
I have a 2000 Rx300 166k I've been driving for 15 years, my favorite car I ever owned! Only drive it locally these days, work, home, grocery, etc.
Was hoping to keep driving it till 200k or more but...

In 2020 CEL was on and took it to dealership. They told me it was some sensor that wouldn't affect driveability, they did point out a valve cover gasket leak.
Got the Leak replaced as well as sparkplugs and general tune-up.

CEL was off for a while, but came back on and started noticing stuttering/chugging when idle at the light after driving for a few minutes. It was bad a couple of times to where engine shut off, but would start right back up no problem. No
acceleration problems.

It didn't do it all the time, very intermitent. I discovered that turning the A/C off diminished the stuttering CONSIDERABLY.
Took it to my mechanic at this point, had it dignosed. Cleaned out the Throttle body. He checked for Coils/Spark plug malfunction, all fine.

CEL went off, came back on a week or two after that and one day, CEL flashing and dinging.
Took it to mechanic immediately. Misfire code, but upon physical check, no missfire detected.
MAF sensor likely bad according to computer read, but that it shouldn't affect drivability.
Drove it for another couple of weeks with the car working better, but CEL still on. Replaced MAF sensor, slight improvement, CEL still on.

One night, car wouldn't accelerate pass 20mph. Pulled over, had it towed. Tow Truck driver revved it like crazy, said potentially Cat Converter clogged.
From there, sent it to a different mechanic to get second opinion.
He plugged it to computer, tested sensors, cat converters, apparently ran a bunch of diagnostics. He said he couldn't find anything and didn't charge me. I thought it odd, but whatever.
Car drove fine off the lot, no chugging, no issue getting up to speed, CEL still on.

Drove it for months after that, till about a month ago, car would not speed past 20-30mph again. RPMs would not go past 2.
I could feel the gear shifting very sluggishly and would hold for a second while accelerating and then a very quick release to the next gear speeding up. Eventually it would get to 40 but VERY SLOWLY, rotten egg odor. At this point I
figured probably bad Cat Converter.

Sent it to my original mechanic to do a deep dive and check.
Below I'll list all ELEVEN codes with the description.
This time, diagnosed with all 3 cat converters bad.
One of the sensors was completely burnt, the other one seemed fine. I believe it was the front bank sensor (2, 4, 6, as I understand it?)

Before I dive into that very expensive repair, I wanted to ask the people of this wonderful forum for opinions/help, in case anyone has dealt with a similar issue.

I've done a ton of research on the matter and it all seems to point to the catalytic converter, however I'm unsure that the original misfire was ever fixed and hence my hesitation for the repairs.
Also, is it possible that all three Cat Converters fail at the same time? Forgive my ignorance, I'm not a mechanic.

If anyone has any ideas or suggestions, I would greatly appreciate the input!!
Below is the list of codes with the explanation given by the scanner. Some of the descriptions are cut off cause I only took a picture of the first screen when it came up.
If you have any questions, I'll try to answer as I remember.

One more thing to point out, not that I believe it to be related, but just in case. The radiator is allegedly about to go bad, but I was told this due to discoloration, not actual failure. There's no leaks or cracks anywhere and the
temperature on the car never went past half way on the dashboard gauge.

Thank you so much for your time!

P1155 - A/F Sensor Heater Circuit (Bank 2 Sensor 1)
P1150 - 1. A/F Sensor Circuit Range/ Performance Malfunction (bank 2 Sensor 1)
2. Coolant Path Clog up for
P1135 - A/F Sensor Heater Circuit (Bank 1 Sensor 1)
P1130 - A/F Sensor Circuit Range/Performance (Bank 1 Sensor 1)
P0172 - System Too Rich (A/F Rich. Bank 1)
P0171 - System Too Lean (A/F Lean. Bank 1)
P0300 - Random/Multiple Cylinder Misfire Detected
P0125 - Insufficient Coolant Temperature For Closed Loop Fuel Control
P0330 - Knock Sensor 2 Circuit (Bank 2) DTC Severity 2 of 3: Repair immediately if drivability issues are present. Threat to essential

 

Hello,

There are a few things to point out.

To start, if you are getting a CEL as frequently, I would strongly suggest to purchase your very own Scan Tool, at the very least you won't be forced to stop by a mechanic every time you need the Codes pulled up. Scan Tools nowadays are really not that expensive, even the Good Quality ones, and are very easy to use, all you need is to plug it in and press a button to select what you are looking to do.

Look for a Scan Tool that has at least some reasonable Brand Name attached to it. Also check that it can not only Read, but also Graph the Engine Live Data, aka the Data from all the Sensors on the Engine as it is Running, Graph Function can be particularly useful for the Catalyst Tests, other than that, they are more or less similar, for all intents and purposes. Here is a Bosch Scan Tool that, if the Video below is to be trusted, has a great set of features for a pretty good price, it can even read some of the ABS Fault Codes, which is not always the case, as it is not a part of Generic OBD2 Standard. It is also capable of Storing the Data that it displays, which can really come in handy when it comes to sharing the Data that you collected here.


Next, I would like to go over the Codes that you have listed. In your specific case though, either not all of those Codes are Active, or something particularly strange happened, seeing the sheer number of Sensors that failed in a very short notice. The fact that you have Codes for the Mixture being too Rich and too Lean all at the same time seems to point to the Former though, as the likelihood of both being true are about as high as going both left and right on the same intersection at the same time. Either way, I would like to go over each of them one-by-one.

Code P0330 - Knock Sensor Failure, is currently the most crucial Code of all the ones you listed, I am surprised that none of the Mechanics that you visited paid any attention to it. I may even go as far as to say that this is what has Started your entire endeavor.

The term "Knock" (also known as Detonation) in this context, to put it very bluntly, is when the Air/Fuel Mixture inside the Cylinder Ignites by Itself, before it is Ignited by the Spark Plug, this can very quickly cause some serious Damage to the Engine if left unchecked, in that case you essentially have two bricks flying towards each other, so something will have to give, usually the Piston. Here is a great article about Knocking (Detonation) if you are interested.

This is why Knock Sensors exist. Again, if simplified, Knock Sensors are essentially Microphones bolted to the Engine Block that Listen to a very specific Frequency, calculated at the Factory, if the Engine starts Resonating at that Frequency, it very likely indicates Engine Knocking. This allows the ECU to react quickly and adjust Engine Parameters, such as Ignition Timing accordingly, here is a thread about Knock Sensors.

For every Sensor in the car there is what's called a Fail-Safe Mode - essentially an instruction Hard-Wired into the ECU on what to do and how to Operate if a given Sensor happened to Fail. Some Fails-Safes are barely noticeable, and some are particularly strict. Seeing the consequences of the Engine Knocking described above, a Fail-Safe Function of the Knock Sensor is about as Restrictive as it gets - to eliminate every chance of the Engine starting to Knock while the ECU isn't looking, the car sets the Ignition Timing (when to Fire the Spark Plug in relation to the Position of the Piston) from ~40° and beyond with the Throttle Opened straight down to 0°, under any and all conditions. In this case, the car Ignites the Air/Fuel Mixture only by the time when it should start heading into the exhaust, meaning that Majority of Energy created during combustion is only heating your Exhaust instead of pushing the Piston Down. This alone could account for the Sluggish behavior that you described earlier, which, again, is why I was surprised that none of the Mechanics gave it a second look.

Next, let's go over P1130/P1135 and P1150/P1155. To be perfectly honest, I suspect that someone, at some point, for some reason, has Disconnected them before, and simply neglected to Clear the Codes afterwards, here's for another good reason to get your own Scan Tool and not trust anyone on their word.

A/F Sensor is there to Monitor how much Oxygen is left in the Exhaust after the Mixture is Combusted. It is done to give the ECU an ability to Gauge the Air to Fuel Ratio that is being supplied into each Cylinder with an impeccable precision, providing both the best performance, and the cleanest exhaust. Due to their Construction, A/F Sensors can operate only after they reach a certain Temperature, this is why they are also equipped with Heaters, which are literally just a very small Boiler Heater Element wrapped around the Sensor designed to keep them warm until the Engine heats up enough to take over. Here is an article about it.

P1130 for Bank 1, as well as P1150 for Bank 2, indicate that the Readings supplied by the Sensors are way outside of Scope expected by the ECU, this could be a result of a Fried Sensor, or a Damaged Wiring.

P1135 and P1155 indicate an issue in the aforementioned Heater Elements of each respective Sensor. This is actually a good sign, as those Heater Elements are exceedingly simple to check, below is a Video on the subject.


The reason I suspect that someone just messed with them is that to see Both Elements of the Sensor fail on Both of the Banks in such a rapid succession is just as likely as it is to see someone get struck by lighting the same number of times in the same succession. Usually when the Sensor Fails, only one Part of it fails at a time, it's either the Heater that melts, or the Sensor itself that fails, it's rare to see both at the same time, not to mention on both sides. That said, guess what would cause both to "fail" with a guaranteed result - if either Sensor is Disconnected with the Ignition on the ON Position, the ECU will trip a Code for both Elements, and those Codes will persist even if the Sensors are then Reconnected, unless they are Erased with a Scan Tool.

The reason I mentioned that having Heater Circuit Codes is a good thing is because that makes it very easy to verify, all you need is a Multimeter and a few minutes of your time. If the Heaters turn out being Intact, those Codes, along with the P1130 and P1150 could be disregarded for now.

I already touched on P0171 and P0172 in the beginning, but I will say it again - those are the opposite Ends of the same Stick, they cannot happen at the same time, either One or Both of those Codes are Not Active (Pending), meaning that the Condition that caused them has since Disappeared, and the ECU just stored the Code away for now, in case if whatever it was that caused either of them returns. They can be Disregarded for now.

P0300 - Random Misfire. Seeing that you have a Knock Sensor Code, it's not a particular surprise that, under some Conditions, the ECU can consider an Incomplete Combustion as a Misfire. With the Ignition Timing set to 0° due to Knock Sensor Codes (see above), you are essentially Rope Walking mere inches away from one of the Cylinder inevitably Misfiring. All this is to say that it is safe to Disregard this Code until the Knock Sensor Fault is Fixed.

P0125, my favorite Code from the list, got to give it to Toyota for finding a particularly creative way of phrasing that the ECU is unable to enter Closed Loop Control, but let's keep everything in order. To start, this Code has absolutely nothing to do with Coolant Temperature, the description that you see is an anachronism of the time well passed. The only task of this Code is to notify you that the ECU is Unable to utilize the Closed Loop Control, without any mention of what in particular is causing said Condition.

Closed Loop Control is essentially what defines the Modern Electronic Fuel Injection (EFI) Engine. It's a Self-Sufficient System designed to run off of Factual, Current Information, without relying on any Calculated or Pre-Determined Charts. To boil it down to one phrase - this is what gives us the ability to Eliminate any and all Guesswork in the Engine Operation.

As an example, the Mass Air Flow (MAF) Sensor is providing the ECU with a rough guideline on how much Air is about to Enter into the Engine, which is used to know exactly how much Fuel to add to the Mixture for a perfect Stoichiometry (the Ratio that allows all Parts of the Mixture to be Consumed during Combustion, in case of Petrol, it is 14 parts Air to 1 part Fuel), and once the Combustion has occurred, the A/F Sensors provide the immediate Feedback on how Precise said Ratio was, which then "Loops" back to the MAF Sensor Data, the ECU can now make Corrections on the fly for any Inconsistencies like Engine Wear, Altitude, Fuel Grade, etc., based directly on the Sensor Data. Think of it as an Excel sheet, where in case of an Open Loop, you are responsible for typing every Cell in by hand, and any mistake you make is on you, whereas the Closed Loop is when you set a Formula for each Cell, relying on just one Standardized and Fool-Proof way of providing a result, eliminating the possibility of any Mistakes in the process. Here is an article on Engine Management.

That said, for the car to Maintain the Closed Loop Control, every Sensor responsible for it must be Perfectly Functional, if even one of them fails and there is no Backup, the will be forced to revert back to the Open Loop Control, operating based off of Pre-Defined Charts. In your case, you have Codes for the Absolute Majority of Sensors responsible for the reliable operation of a Closed Loop Control, so there is very little surprise that you have a P0125 Code Active. As with the Misfire Code, it is safe to Disregard until you deal with all the Codes for the Sensors.


So in summary - get a Scan Tool, even the most basic ELM327 for $5 off AliExpress will go a long way if you could set it up properly, without it, you are in the middle of the forest without a map. Once you have a Scan Tool, Reset all the Codes currently stored in the System, and see what will come back up. The Codes that will come back after the Reset are the Only ones you have to worry about at the moment. As mentioned, I am pretty sure you will get P0330, Knock Sensor Circuit Code back.

It is a bit of a shame, as it does require taking the entire Intake Manifold apart to access them, Knock Sensors are deeeeep in the bowels of the Engine Valley, below is a Video on how to access them. That said, while it may look scary, it's really not complicated, just tedious to keep track of all the parts, but if you are careful and take notes as you go, it is perfectly doable in a Garage within a few days. Doing it yourself can save you a small fortune, especially seeing what little I know about the .. qualitat of your Local Mechanics..


Well, that just about wraps it up, let me know if you have other questions..

Hope this helps and best of luck!

 

Before I go chasing any of the codes, I would suggest check the battery and make sure it is properly charged.

Then note down the codes [you have already done that] and then clear the codes.

start and drive thee vehicle ... observe time for temp gauge to show you 1/2 way point

On the first onset of CEL, read the codes and fix those first.

Salim