I have a 96 850 with 108K that I have been trying to clear engine codes on for some time now. I originally had the code for low counts on the forward O2 sensor, and replaced the sensor. Shortly later, I got, and still have, the P0172 code for rich mixture.

Since the downstream sensor is reading rich, I am assuming that it is good. How likely is it that the new forward sensor has failed, and is measuring too lean, and not throwing a fault code?

Other than the O2 sensors which other things should I look at? Are the fuel injectors suspect at this mileage? Or the cat?

Thanks in advance,

Andy