P1A89

DTC P1A89

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* 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 enable message active.

Conditions for Setting the DTC

42 volt circuit below 21 volts in Normal Mode more than 1 millisecond.

Action Taken When the DTC Sets

* The HPCM stores the DTC information in memory when the diagnostic runs and fails.
* The APM will shutdown 42 volt conversions.

Conditions for Clearing the DTC

APM 42 volt enable toggled to off then back on.

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.
* A 42 volt system voltage low fault may be caused by either an APM that is not capable of delivering the correct voltage/current or a defective EPS drawing too much current.

Circuit/System Verification

1. Start the engine.
2. Verify with the scan tool that the APM is reading the 42 volt voltage correctly.

Circuit/System Testing

1. Turn the Ignition to ON.
2. Verify the HPCM 300 V Circuit Voltage in the APM Scan Tool Data list is up.
3. Use the Device Control APM 42 volt enable to turn on the APM 42 volt system.

^ If the system will not enable, turn the ignition to OFF and then disconnect the 42 volt connector from the APM.

4. Turn the Ignition to ON.
5. Use the Device Control to turn on the APM 42 volt system.

^ If the 42 volt system is OK diagnose the EPS.
^ If the 42 volt system will not enable, replace the APM.

Repair Instructions

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