My car is a 1997 OBD2 California Emissions model.
Currently, there are no DTCs and the MIL is not on, however after considerable driving there are three incomplete emissions readiness self-tests: Catalytic Converter, Oxygen Sensor, and EGR. I can only have a maximum of two incomplete to pass annual emissions inspection. I would like to get all of these items taken care of but currently I am focusing on the cat/O2 and intend to address the EGR later. (I did remove and clean the EGR valve, so perhaps that will take care of that self-test, but regardless I will want to address the cat/O2 situation.)
I have been monitoring O2 voltage through my ScanGaugeII and the rear O2 sensor exhibits the following behavior:
- When at operating temperature and cruising, the rear O2 sensor measures 10% voltage or less, fluctuating between 5% and 10%, roughly in synch with the front sensor (generally reading between 10%-90%).
- When given full throttle and going rich, rear sensor tends to read 85%-95% voltage while front sensor reads 100% voltage.
- When decelerating in gear (overrun fuel cut) and going lean, both sensors read 0%.
Obviously, neither item is far enough out of spec to cause a check engine light, but since I'm not sure exactly what sort of voltage the rear sensor should be producing under normal circumstances, I'm not certain whether the sensor itself is just going bad or whether these readings are indicative of a bad cat. Given the age of the equipment, it could easily be either one, but I'd prefer not to replace either one unless I'm sure it is necessary.
Can someone who is well-versed in these things shed some light for me? Thanks!
Follow-up question: If the cat is bad and needs replaced, will a Federal Emissions cat work just fine or is the California OBD2 computer specifically calibrated to expect a California Emissions cat? Is the Cali cat simply a local requirement (which would not apply since I am in Texas) or does the computer actually require the stricter emissions equipment to complete its self-tests?