P1A8A

DTC P1A8A

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

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 (Connector Views)
Description and Operation

Drive Motor Generator Control Module Description and Operation ()
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Start the engine.
2. 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 (Verification Tests) after completing the diagnostic procedure.

Control Module References (Programming and Relearning) for APM or PSCM replacement, setup, and programming.