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 P064C: Glow Plug Module Control Performance

Diagnostic Fault Information

Circuit

Short to Ground

Open

Short to Voltage

GPCM Battery voltage feed circuit

P064C

P064C

--

Circuit/System Description

The glow control system is operated when the engine coolant temperature is low, which allows easier engine starting. If the ignition switch is turned ON when the engine coolant temperature is low, the engine control module (ECM) illuminates the glow indicator lamp and turns ON the glow plugs. After a fixed time passes, the ECM turns OFF the glow indicator lamp and the glow plugs. The glow plug control module (GPCM) has the ability to perform internal diagnostics for voltage and the output state of the glow plugs. If the GPCM detects a GPCM system voltage error, the GPCM will send a message to the ECM via the controller area network (CAN) communication bus and sets this DTC.

Conditions for Running the DTC

    • DTCs U0073 and U0106 are not set.
    • The battery voltage is between 10-16 volts.
    • The ignition is ON for longer than 2 seconds.

Conditions for Setting the DTC

Either of following condition is met:

    • The GPCM detects system voltage is too low.
    • The GPCM detects any of the glow plug switches defective.
    • The ECM received an error messages from the GPCM.

Action Taken When the DTC Sets

DTC P064C is a Type B DTC.

Conditions for Clearing the DTC

DTC P064C is a Type B DTC.

Diagnostic Aids

A charging system condition may set this DTC.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Verify the integrity of the GPCM power supply or CAN communication circuit by inspecting for the following conditions:

    • Damaged components
    • Loose or improper installation

Circuit/System Testing

Important: You must perform Circuit/System Verification before proceeding with Circuit/System Testing.

  1. Disconnect the GPCM harness X1 or X2 connector.
  2. Ignition ON, verify that a test lamp illuminates between the GPCM battery voltage feed circuit and ground.
  3. If the test lamp does not illuminate, test the battery voltage feed circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the GPCM.
  4. If all circuits test normal, replace the GPCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Glow Plug Replacement
    •  Control Module References for ECM replacement, setup, and programming