GM Service Manual Online
For 1990-2009 cars only

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 P1A56: Hybrid System Voltage Discharge Circuit

Circuit/System Description

The starter/generator control module (SGCM) monitors connector C2 terminals 15 and 16. When the connector is disconnected, the SGCM capacitors are electrically connected to a discharge resistor.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

36-volt output voltage greater than 10 volts and discharge resistance error signal is ON for 1 second.

Action Taken When the DTC Sets

Hybrid system is disabled.

Conditions for Clearing the DTC

Clears 30 seconds after cycle wakeup signal.

Diagnostic Aids

Possible cable open or SGCM internal problem.

Reference Information

Schematic Reference

Hybrid Controls Schematics

Connector End View Reference

Hybrid Controls Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Scan Tool Data List

Circuit/System Verification

Caution: To help avoid personal injury, additional precautions must be taken prior to working on the generator control module or the generator starter. After removing the 36V battery cables from the generator battery, remove both engine wiring harness connectors from the generator control module. Wait at least 5 minutes and then remove the generator control module cover. Verify voltage levels at all 36V, 12V, and 3-phase connections, are less than 3 volts using a DMM before proceeding.

  1. Inspect harness connector C2 connection to the SGCM.
  2. If there is nothing wrong with the harness connector, replace the SGCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for SGCM replacement, setup, and programming.