Diagnostic Instructions
DTC Descriptor
DTC P1A8A: 42 Volt System Voltage High
Circuit/System Description
The Accessory Power Module (APM) supplies the energy that flows between the high voltage, 300 volt, direct current (DC) and 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. 42 volt APM functions will run only when the 42 volt APM enable is active on the high speed hybrid GMLAN
communication circuit.
Conditions for Running the DTC
APM 42 volt output commanded on.
Conditions for Setting the DTC
APM 42 volt circuit above 50 volts for more than 3 seconds.
Action Taken When the DTC Sets
| • | DTC P1A8A is a Type C DTC. |
| • | The APM will shutdown 42 volt conversions. |
Conditions for Clearing the DTC
| • | DTC P1A8A is a Type C DTC. |
| • | 42 volt circuit is below 48 volts. |
Diagnostic Aids
| • | DTC C0895 07 EPS Voltage Above Threshold may be set. |
| • | The APM Data List on the scan tool contains a parameter named 42V Circuit Maximum. If this parameter has a voltage that is greater than 50 volts, the protection circuits in the power steering control module (PSCM) have failed and as
a result, this is not a fault condition in the APM. |
Reference Information
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
Circuit/System Testing
- Start the engine.
- Using the scan tool, observe the 42V Circuit Voltage parameter on the APM data list.
| ⇒ | If the 42V Circuit Voltage parameter is greater than 48 volts, replace the APM. |
| ⇒ | If the 42V Circuit Voltage parameter is less than 48 volts, replace the PSCM. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Control Module References
for APM or PSCM replacement, setup, and programming.
