Check Engine Light

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Mar 28, 2003
The check engine light on my '96 went on the other day. I went to Autozone and the diagnostic code pointed to the O2 sensor. I know that there were posts on the old site about this but....

What's the next step to resolvingthis problem?


What was the exact code or codes pulled. There are several that pertain to O2 sensors.......We need more specifics to be able to assist you..........
The code is P0420 - Catalyst efficeince below threshhold.

The guy at AutoZone reset the light and it didn't come back immediately.

What next?
I had that same code come on and was reset about 800 miles ago and has not come back on.

I am not going to worry about it until it comes back.


&nbsp:Did you save the posts on that?

I can lookup the info and re-post if need be.......

Regards...Dan :beer:
Na, cruiserdan, the post scared the heck out of me and I did not save it. However, it went something like this...

1)Check/ replace front O2
2)Check/ replace rear 02
3) Check/ replace CATs


I reset mine and it has not come back on after many miles and very variable driving conditions. I have my fingers crossed that something passed through that the sensors did not like.......
DTC code P0420:

"The ECM compares the waveform of the oxygen sensor located before the catalyst with the waveform of the oxygen sensor located after the catalyst to determine whether or not catalyst performance has deteriorated."

Trouble area:
Three way catalytic converter
Open or short in heated oxygen sensor circuit
Heated oxygen sensor

Repair sequence:

Check sensor 1, bad...replace. ok....check sensor 2, bad....replace. ok.......replace three way catalytic converter....

Regards....Dan :beer:

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