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Check Engine Light 2000 Le 94k Miles




Guest mozezman

Hello All, I am new to the forum so please excuse the newbie,

To start off I've done a lot of reading and searching on this forum about check engine lights, catalytic converters and oxygen sensors....

I've recently purchased a 2000 Corolla LE for my wife with 94K miles on it. About a week ago the CEL came on.

I've decided to try and sort out this problem myself (I persuaded her to buy a corolla)!!!

I want to do this right, I don't want to be killed by a dealer and I am quite handy with some mechanical stuff (i,e I will do most of the work on my own).

So...here's what I did....

1. I brought a small OBD-II scanner and read the code. P0420- Catalytic Eff. Bel. Thresh.(Bank 1).

When reset, the engine sounded much quiter (smooth idle) and fuel consumption improved. A friend has suggested that the oxgen sensor could be bad.

Is there any way to do more investigation to pinpoint wether it is specifically the oxygen sensor that is faulty?

I also believe that there are 2 oxygen sensors on the corolla, one pre and one post. Is one more likely to fail than the other?

Are there any witeups/ pics showing location of oxgen sensors and removal/installation notes? I am happy to document these and post if I get to replace the oxygen sensors.

Any help is much appreciated

The OBD-II code P0420 Catalyst System Efficiency Below Threshold (Bank 1) basically tells you that the difference in voltage signals between the upstream and downstream O2 sensors (pre- and post- cat sensors) is not high enough. Could be a bad O2 sensor (usually front one) or bad catalytic converter. The only way to tell for sure is to backprobe the O2 sensors and measure the voltage signal coming from it. If the voltage doesn't change very much (signal is almost sinusodial) - then the O2 sensor is bad. If both sensors check out - then it is a bad cat.

This is assuming that there is nothing else wrong with the car - ie., it runs well otherwise.

Chances are - since this was a used car - the front O2 sensor was going bad and slowly burning up the cat, but not enough to trip a trouble code (or previous owner kept resetting it instead of fixing it). A misfire will also lead to a dead cat eventually - usually a P0420 code comes up with a P0300 misfire code. Sometime is it caught by the OBD-II sometimes not. But since you mentioned, when reset, car runs better and uses less fuel, leads me to believe that a O2 sensor is going out or engine has too many misfires. I'd check the condition of the ignition and fuel injection system (8th generation Corollas seems to have problems with those and emissions related issues). If those are good - probe the O2 sensors (or run the OBD-II sensor in data aquisition mode, if applicable) and see if they are OK.

Good Luck.

Guest mozezman

Thanks for replying fishexpo101.

I am going to check out the pre cat oxygen sensor and see if it okay. If not I will replace and see if that cures the problem.

Thanks

I'll keep you informed of what happens.

P.S Do you know of a good place to get oxygen sensor parts other than the standard retial options?

Some have reported these sites as good:

www.1sttoyotaparts.com/

www.rockauto.com



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