ok i have a 95 xj 2wd 4.0 i have no check engine light. but i just got a new obd1 reader so to test it out i hooked it up i got 6 codes. 4 codes and 2 duplicates. i got 21 42 43 and 47 i know what the codes mean but my question is y isnt the light on? yes the light works. im thinking they are saved codes. it already has a new alt. and battery any suggestions.