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Home >> Pontiac >> 2001 >> Firebird Formula, Automatic >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 5.7L >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Code Enable Criteria
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Code Enable Criteria

For DTC to run, engine must be running. DTC will set when PCM detects a voltage out of tolerance condition on 5-volt reference 2 circuit for longer than 10 seconds.