P1A8A

DTC P1A8A

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 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 enable message active.

Conditions for Setting the DTC

APM 42 volt circuit above 50 volts for more than 3 seconds.

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

42 volt circuit falls below 48 volts for more than 0.012 seconds.

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 EPS have failed and as a result, this is not a fault condition in the APM.

Circuit/System Verification

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

Circuit/System Testing

1. Elevate the vehicle enough to freely spin the front tires.
2. Turn the Ignition to ON.
3. Use the Scan Tool Device Control APM 42 volt enable to turn on the APM 42 volt system.

^ If the 42 Volt Circuit is reading greater than 48 volts without the steering wheel being turned, replace the APM.

4. Rotate the steering wheel to the right lock position.
5. Exit the vehicle and grasp one of the front tires. Force the steering to the left lock position.
6. Observe the 42 Volt Maximum Voltage in the APM data list.

^ If the voltage is greater than 50 volts, the EPS protection circuitry internally to the EPS has failed. Diagnose the EPS.

Repair Instructions

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