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International Automotive Technicians Network
Re: GM 3.1 Ignition diagnostics
Posted to Technical Tips Forum on 2/12/2001

Robert,

With the code 42 you may have an ICM problem. This can also be an ECM problem. Do an ECM tap test. You are probably on the right track. Monitor the CKP and REF together. CKP with a REF failure = bad ICM if the powers and grounds are ok. For more deta... Login to read more.