P1A89

DTC P1A89

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 P1A89
- 42 Volt System Voltage Low

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

42 volt circuit below 21 volts during operation.

Action Taken When the DTC Sets

* DTC P1A89 is a Type C DTC.
* The APM will shutdown 42 volt conversions.

Conditions for Clearing the DTC

DTC P1A89 is a Type C DTC.

Diagnostic Aids

* DTC C0895 03 EPS Voltage Below Threshold may be set.
* DTC C0895 12 EPS Voltage Below Minimum Threshold may also be set.
* The 42 volt circuit is only used by the EPS. The APM can apply 42 volts on the connector without being connected to the EPS.

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 Verification

1. Start the engine.
2. Using the scan tool, observe the 42V Circuit Voltage parameter on the APM data list.

• If the voltage is less than 40 volts, proceed to Circuit/System Testing.

3. Rotate the steering wheel back and forth while stationary.

• If the voltage is less than 40 volts, the EPS is drawing excessive current. Replace the power steering motor.

Circuit/System Testing

1. Disconnect the 42 Volt harness connector at the APM.
2. Turn the ignition to ON.
3. Use the APM Intermediate Voltage Control on the scan tool to turn on the 42 volt circuit.

• If the voltage is greater than 40 volts, replace the power steering control module (PSCM).
• If the voltage is less than 40 volts, replace the APM.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Power Steering Assist Motor Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for APM or PSCM replacement, setup, and programming.