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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1358 (Hybrid Controls - DTC P181C To DTC P2797) >> DTC P1A88 >> Circuit/System Verification

Circuit/System Verification

WARNING: This page is about a different car, the 2009 GMC Sierra and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. This DTC can set as a result of conditions external to the APM. Before attempting to diagnose this DTC, ensure the following conditions have not been encountered:
    • High voltage contactor relays opening any time the APM is doing 42 volt conversion.
    • The high voltage system is greater than 390 volts or less than 216 volts during 42 volt conversion. Extreme cold weather conditions may occasionally cause the high voltage system to be greater than 390 volts.
    • The 12 volt circuit is less than 6.7 volts during 42 volt conversion.
    • A short circuit condition on the 42 volt circuit which causes the APM to produce greater than 60 amps.
    • If any of the above APM-external conditions have occurred, diagnose the conditions as applicable and clear the DTC Information. No further diagnosis of this DTC is required.
    • If none of the above APM-external conditions have been encountered, continue with Circuit/System Verification.
    2. IMPORTANT: Do not turn the ignition to START.
  2. Turn the ignition key to the RUN position. Ensure that the high voltage contactor relays close. Do not go to START.
    • If the high voltage contactor relays do not close, diagnose the DTC or symptom that is preventing them from closing before attempting to diagnose this DTC.
  3. Test for DTC P1A88.
    • If the diagnostic is set as Last Test Failed/Current, replace the APM.
  4. Start the engine.
  5. Test for DTCs P1A89, P1A8A and P1A8C.
    • If any of the above diagnostics are set, diagnose those first.
  6. After the engine has started, retest for DTC P1A88.
    • If the diagnostic is set as Last Test Failed/Current, proceed to Circuit/System Testing.
    • If the diagnostic is set as Last Test Passed, the external condition that set this DTC is no longer present. Clear the DTC Information. No further diagnosis of this DTC is required.
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