I need to put something to rest once and for all. I have a 2000 4Runner, 3.4 LV6, auto, 4x4. My check engine light is on for the fourth time in the past six months. Does anyone know all the inputs that can trigger the "check engine" light to come on? Are there like a thousand or just a handful? I ask because so far I have replaced the Mass Air Flow Sensor and the O2 sensor before the catalytic converter, and I'm wondering if the other O2 sensor is now shot and if this is the last main thing that inputs into this light. Thanks for any help.
Gus

Yes, there are tons of things that can cause the light to come on.

You need to have the code checked with a scanner. AutoZone has a basic scanner that they will hook up to your truck free of charge. The dealer has a more advanced diagnostic scanner that they hook up and pinpoint the problem.

I'd first start at AutoZOne and see if its something simple.

Thanks Adam. I was wondering do you or anyone else out there have a list of everything that can cause the "check engine" light to come on? Thanks

Gus

LIke you said, theres millions of things. Ok, maybe not millions, but theres a ton of sensors and switches that can go bad and set off the light.


Take it to AutoZone, have it read, come back here and tell us exactly what code it was. Could be something as simple as a loose gas cap.

There's probably a good chance that nobody has a whole list for you. The best thing to do is to just go and get the code read.

There are simply too many reasons that would trigger the lamp to list. Codes must be interpreted in a case by case basis.

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The diagnostic code is P0420 (described as something like Lean exhaust bank II). Is this the O2 sensor after the catalytic converter sending in this signal? And if so, how can I check to see if it is the O2 sensor that is bad vice the catalytic converter itself? Thanks for any help.

Gus

420 is catalyst system efficiency below threshold. Just went through that one. Went the cats start to go bad it will trigger that code especially when driving slow where the cats don't stay lit up. Eventually it will just trip all the time.

There is one cure and only one. Replace the cats. If you are in CA there are two cats. Non CA models there is one but CA models are sold outside CA. Don't bother visiting the dealer. They are at least a $1000 each. I shopped around and the best I could do was Midas for about $1000 for both installed. Outside CA you can buy them for $200 each and put them in yourself. They just bolt up.

Lars,
Thanks for your reply. Question for you, if I hold off on replacing the catalytic converter, does that harm the vehicle or affect its performance? And also, how can I tell if I have one or two cats? Thanks.

Gus

Not sure if this will help you, but we use this system for checking fault codes.

http://www.auto-diagnostic-codes.com/Petrol-Engine/Japanese-Korean/Toyota-Engines.html

I checked out that link, but they don't cover Toyota. Not that I could see. Thanks anyway.

v/r
Gus