YJ's are OBD1, so no oil change... Could be the O2, but I dont know... This is one of the reasons I bought a scanning tool compatible with the YJ; reading the dash light was a PITA!!! By the way, you are aware that there is a trickto read the codes by turning on and off the IGN switch, right? Then the CEL light will blink to indicate the code. Counting, however, is not as simple as it sounds...