As the title states... I have a 92 4.0. I decided to check for any codes just for sh**s (my mpg decreased a little bit with no change in driving) and it threw code 12 and 21. I know 12 is battery recently disconnected, although I haven't recently disconnected it. Is it a thing for the XJ to think it's been disconnected recently from time to time?
The second code is 21, which I believe means bad O2 sensor. My question is, how many O2 sensors does a 92 4.0 have and where are they?

Thanks in advanced CFers!

 

I think a '92 only has one O2 sensor. I may be wrong though. I had a '92 and currently have a '91 and my '91 only has one on it.

 

Thank you for your reply. I hope you're right BC that'll save me about $50!

Any other input on the matter CF?