[Zilla]

Is the O2 sensor on my 2000 Ody Ex considered "upstream" or "downstream?" I just failed inspection (in the Raleigh, NC area) since I put a non-fouler to avert the P0420 code, and I may have to just replace it. I'll take it to a second place tomorrow to see it if passes there. Thanks!

 

[OdyinNH]

It has 2 O2 sensors. One is upstream and one is downstream. The one closer to the engine is upstream. One screws into the exhaust pipe before the cat I think and the other screws into the cat.

 

[redmondjp]

So wait a minute - they failed you due to the visual inspection, or is your check engine light on now?

 

[sontakke]

I suspect when he put the non fouler, he might have either twisted the wire going to that sensor badly and/or the sensor itself went bad during the removal and reinstall. He might be getting a rear O2 sensor code, more likely something about the rear O2 heater circuit. But this is all guess on our part. I can't imagine any inspection station catching the non-fouler on a visual. Most states just hook up scanner to the OBD port and don't even put the vehicle on the lift.