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I would begin at this point by having a 2nd measurement point - e.g.: run the car and see what an exhaust gas analyzer says. Maybe zero O2 sensors were bad.

I'm not sure how the computer determines that an O2 sensor is bad. It could get an implausible signal, maybe. I guess the question is, how does it measure the result? What in THAT chain could malfunction?

This is the problem with simple error codes. It eliminates thought. 99% of the time that's an improvement, but the other 1% of the time it causes trouble and dead ends.

My experience is that the 02 sensors and cats on these cars (and most others) are very dependable. Moreover, failures are generally gradual as they go out of calibration.

Grant

I would begin at this point by having a 2nd measurement point - e.g.: run the car and see what an exhaust gas analyzer says. Maybe zero O2 sensors were bad.

I'm not sure how the computer determines that an O2 sensor is bad. It could get an implausible signal, maybe. I guess the question is, how does it measure the result? What in THAT chain could malfunction?

This is the problem with simple error codes. It eliminates thought. 99% of the time that's an improvement, but the other 1% of the time it causes trouble and dead ends.

Grant