Check Engine Light Off!

[phasor]

Hello members,

I have a 2000 Avalon with 80000 miles. My CEL came ON about 2 months ago. I found out by going to the dealer that the code was P0171 which is Fuel Too Lean. The dealer suggested replacing the A/F (Air Fuel) Sensor. There are two A/F Sensors (one for each bank; each bank consists of 3 cylinders) but he could not tell using the Diagnostic Troubleshooter which one needed to be replaced. Each sensor is $300, so I stood a 50% chance that I would have to Shell out an additional $300 if the wrong one was replaced (the two a/f sensors have different part numbers due to different connectors so they cannot by interchanged). I noticed that the car mileage was not affected, nor was the smooth ride affected. So instead of taking the gamble, I decided to continue driving with CEL ON. It was a distraction but I ignored it as best as I could. Occasionally, I would go to Auto Zone (which checks trouble codes for FREE) and talk the guy into clearing the code and thus turn the CEL OFF, but the light would come back ON after 20-30 miles. I have put 5000 miles on the car so far and I have had no problems with its performance. The CEL has been ON all this time.

An interesting thing has happened recently....My CEL would turn OFF by itself at times and come back ON after a few miles. It has turned OFF by itself yesterday and has not come back ON so far (60 miles and counting). No the the CEL bulb is not out since I can see it during the ignition cycling.

My question is that does the Engine Control Module relearn and clear the diagnostic codes it has stored or is this some kind of fluke (or a potential problem).

Your input is appreciated.

[phasor]

:( My CEL came back ON 80 miles later

[Johnr0836]

I have a similar problem. The dealer wants to replace half the injectors. Did you do anything with your car? My VSC light and VSC OFF light are also on. The dealer told me that the three lights are related. (BS) I can get the CEL to blink at WOT.

John

[phasor]

No I have not done anything special to the car. I watch my mileage to make sure it has not changed. The drive is not affected. I have put 10,000 miles since this CEL issue started. I am not sure about the VSC light. What does it stand for? Does the code on the diagnostic tool just say P0171 for you or do you have other codes also set. What does WOT stand for? Is your performance or mileage affected?

[Johnr0836]

VSC is Vehicle Stability Control. (Anti-Skid). P0171 is the only code I'm getting. Performance seems about the same but it's my wife's car and I hardly ever drive it. I have a G35, much more fun than the Avalon. I don't know about the mileage but I would suspect it would be better if the car is running lean. WOT is wide open throttle; pedal to the metal. I'm going to try the poor man's reset (disconnect the battery) tonight and see what happens.

I'll let you know how it works.

[xinwan]

Looks familiar.

My '00 Solara had check engine light on about three weeks ago and OBD II scan says it's a shorted bank 1 sensor 1 oxygen sensor. The dealer must've been crazy to charge me 2.5 hour labor for replacing the sensor so I said forget it.

It could've been a lot eaiser to replace if the sensor was bank 2 sensor 1, the one right in front of you when the hood is open. But the bank 1 sensor 1 can only be reached from the bottom.

Anyway, I'm about to get a digital multimeter to test the oxygen sensor before placing a order for it ($100-$130). Now, today the TRAC OFF light came on and stays on when engine is running. The TRAC OFF switch works only in KOEO (key on engine off). Once engine runs, the TRAC OFF lights comes on in a few seconds and cannot be turned off.

Disable the Battery can reset the check engine light and I haven't tried to see if it works for TRAC OFF light too. But by design, OBD II will report the problem by setting the check engine light on again if the problem persists in two full driving cycles. Are these two lights related or a certain mileage past after the check engine light on triggers the TRAC OFF light? I checked brakes and checked ABS test code. They are all good and the engine runs good although in open loop because of the failed oxygen sensor so I guss I can keep driving the car until I have time to sort out the oxygen sensor problem first. Maybe by that time, TRAC OFF will go away too. Let's just hope.

I don't understand why it happend on a very well maintained low mileage (32k miles) car. My neglected nissan is 7+ years old with nearly 100k miles and only purge valve failed once which triggered the check engine light.

[Johnr0836]

Is the TRAC light the same as VSC? The dealer told me that the CEL and VSC lights are inter-related. I don't believe that. It would be really great if the manufacturers would distribute the information about these systems. I don't believe a word the dealer tells me about what may be causing the lights to go on.

I reset the light on our Avalon last night. I'll let you know how long they stay off.

[phasor]

You can also try your friendly Autozone guy who can lookup the code for you and also erase it for you. Did your VSC & CEL come ON at the same time?

[Johnr0836]

Both lights come on at the same time. They're back on again after I did a reset. Toyota told me there is a connection between them but I doubt that. I'm going to try to pick up a service manual to research this further. Has anyone tried to run a fuel injector clearer through their car?

[phasor]

Yes, as a matter of fact I have used them. I get them from Walmart. I could not tell a lot of difference in performance, but the mileage on the display seemed to go up a couple of miles for a short time.

[Johnr0836]

From another web site I learned that the VSC lights can go on with the CEL light. Also A P0171 can be the result of a dirty Mass Air Flow Sensor. Since my car was in the body shop for almost two months its possible that the sensor is dirty. I'll look into getting it clean and let you know what happens.

Follow-up

Took car to independent mechanic. He diagnosed one bad injector. Replace injector and car is running fine. Toyota wanted to replace 3 injectors.

[phasor]

Come to think of it...I had my air filter replaced about the same time when this issue started. Maybe I have been looking in the wrong place also. Please let us know about your Mass Air Flow Sensor. I will look into my air filter box and see if I can notice anything.

[xinwan]

I think TRAC (traction control on toyota) and VSC (vehicle stability control) use similar technologies, maybe a bit more in VSC. It should monitor wheel speed and lock, then regulate engine output, apply brakes when the traction/stability is out of normal range.

In my case, the OBD II scan reports two error codes all saying bank 1 sensor 1 O2 sensor is bad. I can't quite relate this to my TRAC OFF light unless something else went wrong. Malfunctioning O2 sensor may not report O2 data to ECU at all but ECU still is able to cut off fuel to the engine when traction is lost. And the TRAC OFF light came on about three weeks after check engine light had come on.

[oakz]

in m 2001 solara, v6 sle model, my CEL light came on about 2 days ago.

then last nite, trac control light came on as well and stays on.

dealer first suggested re-tighten gas cap and pull EFI fuse for 30 seconds to see if its pressure realted in the emissions system. well my gas cap was tight and pulling the fuse for 30 seconds didnt seem to reset anything.

was going to consider the "poor mans reset" with the positive Battery terminal tonite to see if that will clear it permanently. But my suspicion is there is actually something wrong.

can bad gas cause these types of problems? in ontario, we have very filthy gas, and with todays prices, i dont feel like buying high test fuel.

I'm interested to hear how the rest of you made out, in particular the gentleman who had the exact same 2 lights on as I did.

the car has 81000 kms on it.

almost seems like a predictable trend, at least as i read this thread.

[taylor618]

I have the 2000 Celica. I had it for about 3 months when the check enginge light first came on. We repeatedly had to turn it off. Finally They replaced the charcoal filter and the gas cap and it was fixed. However there is a certain sequence to the gas cap you are suppossed to do in order for the light not to come back on for that reason. It is turn off engine, pop the tank door, unscrew cap, pump gas, DO NOT pump any more gas after the pump stops on its own, screw gas cap on till it pops several times, shut door. THen the light started coming on again about a year later. I kept ignoring it thinking it was probably the same thing because I hadn't noticed anything performance wise. Finally had them check the code and it had to do with O2 sensor. Had it replaced and light came back on. The dealership said if the O2 sensor was bad for so long then it could have messed up the catalytic converter, so that was replaced and it stayed off. Last month it came on again, I haven't had it checked yet but due to the way it starts, we are going to do new plugs, replace fuel filter and have injectors cleaned. Plan on doing all this ourselves considering high mileage on vehicle, why pay dealership high$$$ when husband is a mechanic!!