Today the check engine light went on, I retreived the diagnostic code per my Haynes manual, and it's #28. Per Haynes this is the Post Catalytic converter, a diagnosis of "open or shorted circuit in the post catalytic converter oxygen sensor circuit." OK, I think I kinda understand....I read a bit further, specifically re testing the oxygen sensor...I think I could do all this... But I wonder, does the code just mean I should replace the second sensor? BTW, I reset the codes, ran the cruiser again, and no check engine light comes on. Could it be a fluke? Any and all help is welcome!