The accessory dc power control module (APM) converts the energy that flows between the high voltage, 300 volt, direct current (DC) to intermediate voltage, 42 volt, DC to support the electric power steering (EPS). The APM receives a 42 volt enable command from the hybrid powertrain control module (HPCM) over the high speed hybrid GMLAN communication circuit.

The APM continuously monitors the status of its 42 volt circuitry. It will do some diagnostics on this circuitry when the ignition key is first turned to RUN. Additional diagnostics are run while the APM is doing 42 volt conversions after receiving the 42 volt enable command.

DTC P1A88 is a Type C DTC.

Schematic Reference

Hybrid Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Drive Motor Generator Control Module Description and Operation

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

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.

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.

Important: Perform Circuit/System Verification prior to performing Circuit/System Testing.

1. Turn the ignition key to the OFF position.
2. Disconnect the 42 volt X2 harness connector at the APM.
3. Turn the ignition key to ON. Do not go to START.
4. Use the scan tool APM Intermediate Voltage Control under the APM special functions list to turn on the 42 volt circuit.

⇒	If the APM Intermediate Voltage is not between 40 and 44 volts, replace the APM.

⇒	If the APM Intermediate Voltage is between 40 and 44 volts, the problem is not in the APM. This DTC can set for the following external reasons:

•	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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for APM replacement, setup, and programming.