Check engine light
 

My 2003 4runner sport has a check engine light on. Also the traction control fault light (VSC TRAC ) light comes on at the same time. An OBD II reader gives a code of PO136 which has something to do with the left bank downstream 02 sensor. I replaced the 02 sensor and reset the code. After about 25 miles both lights come as before. Any Toyota techs out there have an idea what this could be? Help appreciated. Thanks.

I'm no tech or expert, but it would seem that you would have two problems because your Trac/VSC has nothing to do with your 02 sensor.

Not necessarily.

There could be a problem that is common to both, such as a bad ground or the ECM itself. Or there could be a problem with the instrument panel which causes both lights to light when there is a problem with one of the two systems, or maybe both lights are lit due to an instrument panel problem when there is no problem with either system.

As far as the O2 sensor code itself, just because there is an O2 code doesn't mean the O2 sensor itself is bad. It's very possible that the O2 sensor is simply doing it's job by telling you there is a rich or lean condition caused by some other componant (MAF sensor, fuel pressure regulator, plugged fuel filter, vacuum leak, etc.)

In that situation, replacing the sensor wouldn't fix the problem.

Did you check for a trouble code after replacing the sensor? The reason I ask is because it could have been an old code that had been stored in memory (which you cleared when you worked on it), and the light could have been caused by something else (such as an instrument panel problem).

I would check for codes again.

I went round and round last year with two Toyota dealers on my engine warning light. I was told, that for some reason it triggers the traction control, turning it off. I did not like both lights on, plus I like traction control when the roads are slick..
It turned out to be my Cat. Converters. They both needed to be replaced.
We tried everything, isolating the different 02 sensors etc. Nothing worked.
I ended up replacing both. (front pair of cat converters, just down from exhaust manifolds.)
Pretty expensive fix, ($1,400) it was the only solution..
Ironically, after the replacement was done, the light came back on. They found a wire disconnect above the transmission. I was upset to say the least thinking it was the problem all along.
I trust the service guy, and he told me the wire discontect could not have caused all the warning lights.. I have to believe it or :bang:

Good luck..
BTW I rolled 180,000 yesterday..
Jeff

Thanks for all the replies. Could be the Cat converters, I think they are still under warranty till 80,000 miles. I'd like to slap the engineer that designed the VSC TRAC light coming on with the check engine light. Especially when there is nothing wrong with the Traction control? I'm paranoid about the dealer throwing expensive parts at this problem and still having the check engine light come on. Will post the solution when fixed.

the vsc and trac. lights come on because these systems will also control the engine to help maintain traction. When the check engine light comes on with certain codes, the other lights come because the normal ecm shuts them off to prevent harm to the engine if it is not operating properly.