Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | 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 LowCircuit/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
Connector End View Reference
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 Verification
- Start the engine.
- Using the scan tool, observe the 42V Circuit Voltage parameter on the APM data list.
- Rotate the steering wheel back and forth while stationary.
| ⇒ | If the voltage is less than 40 volts, proceed to Circuit/System Testing. |
| ⇒ | If the voltage is less than 40 volts, the EPS is drawing excessive current. Replace the power steering motor. |
Circuit/System Testing
- Disconnect the 42 Volt harness connector at the APM.
- Turn the ignition to ON.
- 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 after completing the diagnostic procedure.
| • | Control Module References for APM or PSCM replacement, setup, and programming. |
