O2 Sensors -- 2 for A/F and 2 for ??
 

It's my understanding that the front 2 oxygen sensors are used to calculate what the A/F ratio should be and the rear ones are used to determine if the cats are doing thier job.

My question is, does the PCM make any adjustments at all based on the rear O2 readings or are they just there for emissions reporting when a scanner is hooked up?

Thomas.

The pcm does not use the rear O2s for any calculations. They are only there to watchdog the cats (hmm, a funny :p ), part of OBD-II.

LOL :) Thats exactly what I needed to know!

Thanks Shoebox,
Thomas.

The front O2's look like this and the rear ones look like this

I don't know if they are mechanically the same, but as the pics show, the connectors are different; so, no, you can't just swap the fronts and rears to see if that's your problem :(

Thomas.

edit: I just noticed you have a '95, isn't that ODB I? If so, doesn't OBD I only have 2 O2s alltogether? I think OBD II ('96+) started with the extra O2 sensors after the cat ....