if your check engine lights works not on but when you turn the key on it luminates there is a real expensive tester that works for all gm obdi take a paper clip unwind it straighten it out bend it in half insert one end into one hole and the other end into the other hole get pen and paper turn key into run engine off position the check engine light will start blinking count blinks beteween a brief pause ++++ +++++++ example 47 +++ +++++ 35 a dodge is a lot easier key on/off 3 times final turn leave in on position a form a old analog meter leads into obd port same a paper clip hope this helps ya