GM Repair Questions? Ask a Mechanic for Answers ASAP
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This problem is usually the instrument cluster or PCM. You will teat the circuit before condemning the PCM. Use a scan tool to verify coolant & fuel gage data , compare to cluster. If it looks good at the PCM the problem is most likely the cluster. Test the wiring from the PCM to the cluster for a good circuit. Here is a schematic to help.
Left side of the engine compartment, forward of the strut tower, inside the air filter box