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99 safari won’t pass smog with no check engine light

Josepb916Josepb916 Member Posts: 1
edited December 2020 in GMC
I have a 99 Safari and it have no check engine light but when u turn the key over but not start it the check engine light will come on every other time. And it failed bc of that thought it was bad bulb changed it still doing it I have no clue what is causing that.


  • thecardoc3thecardoc3 Member Posts: 5,745
    The lamp is directly controlled by the engine control module. The instrument cluster provides the power and the engine controller grounds the circuit to turn it on. A professional level scan tool can be used to command the light on/off which can help during testing. The command circuit goes from pin #2 of connector "A" of the instrument panel to pin #5 of connector #4 of the engine controller. This is a brown wire with a white tracer. This is the information that you need to test to prove what is wrong. The problem can still be in any portion of the circuit.
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