I've been doing some searching on google and have found quite a bit of info on the code and it being related to the 02 sensor. I've already replaced the old sensor, tightened up all my exhaust bolts, changed my fuel filter, cleaned my injectors (703 injectors btw), and have no vacuum leaks. My CEL still comes on every once in a while and every time it's a code 12 and 21 and I was wondering if any of you guys had any other advice on things I could check. It's a '95 cherokee sport btw.

 

1. What sensor did you use to replace? Lots of crapola sensors available. The best sensor for your XJ is NTK. It's the exact OEM replacement to what was in your XJ when it came off the factory line.

2. Inspect every inch of wiring for your oxygen sensor circuit.