Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit/System Description
The accessory power module (APM) supplies the energy that flows between the high voltage (300 volt) direct current (DC) and low voltage (14 volt) DC to charge the 12 volt battery and power accessories. The APM receives a wake-up signal on a discrete line from the serial data gateway module (SDGM) when the key is turned to RUN. After a successful engine start, the APM receives an enable command from the hybrid powertrain control module (HPCM) over the high speed hybrid GMLAN communication circuit to begin power conversion.
Diagnostic Aids
A poor connection at the B+ terminal of the APM or blown 200 Amp Mega-Fuse in the hybrid BEC will prevent the APM from powering up and all values in the APM data list will read zero on the scan tool.
A poor connection on the APM wake-up signal X1 Terminal 3 from the SDGM will also prevent the APM from powering up and all data values in the APM data list will read zero on the scan tool.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Drive Motor Generator Control Module Description and Operation
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Circuit/System Verification
Engine ON, observe the charge indicator on the instrument panel cluster (IPC) or message in the driver information center (DIC). The charge indicator on the IPC should be turned OFF and the DIC should not display charging system message.
| ⇒ | If the charge indicator is not on the IPC or a charging system message is not displayed on the DIC, refer to Testing for Intermittent Conditions and Poor Connections . |
| ⇒ | If the charge indicator is on the IPC or a charging system message is displayed on the DIC, refer to Circuit/System Testing. |
Circuit/System Testing
- Ignition ON, verify that no generator or battery current sensor DTCs are set that would cause a charging system concern.
- Ignition OFF, measure the voltage across the battery terminals. The voltage should read 12.0 volts or greater at room temperature.
- Connect a carbon pile tester to the battery.
- Start the engine and turn all accessories off. Observe the voltage reading on the tester. The voltage should read between 12.6-15.5 volts.
- Adjust the carbon pile tester so that the 12 volt current on the APM data list is reading 175 amps.
| ⇒ | If DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle . |
| ⇒ | If not within specified value, refer to Battery Inspection/Test . |
| ⇒ | If not within specified value, replace the APM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for APM replacement, setup and programming.
