O2 Sensor Problem in 97 Geo Prizm

This problem is very common on European cars. I haven't seen it in a lot of Japanese cars like yours, but I have on some of the higher end ones. A lot of the time the front 02 sensor starts to go bad, but does not set a light. The incorrect information it sends to the computer changes the way the engine runs and leads to the destruction and/or degredation of the rear 02. Sometimes the front 02 is going to hell and that condition is manifested by a trouble code in the rear 02, which is picking up bad air mixtures from the cat because the engine is running too rich or too lean (in this case there's nothing wrong with the rear 02 and it probably doesn't need replacement). Either way, I would suggest starting with the front 02, even though that's not what the code suggests.

Dave D

snipped-for-privacy@gmail.com wrote:

If the code is the HEATER CIRCUIT then check the wiring for being burned to the exhaust or the like. Then check the fuses, I think that car will use 12v from the fuse box for the O2 heater. If you car is a 4 cyl it will only have 2 O2 sensors. Sensor 2 is the rear (after cat) sensor.

well, kinda, I guess. What you describe could happen but it most likely will degrade the cat not the rear sensor. What happens is the front O2 gets weak which makes the car run a little rich. This will ruin the CAT. You would then get a code for cat inefficiency because of the rich mixture, over time, killing the cat. Either way, sounds like his code was the rear O2 heater circuit, not O2 per say.