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/High Resistance

Short to Voltage

Signal Performance

Battery Positive Voltage

P064C

P064C

--

--

Ignition 1 Voltage

P064C

P064C

--

--

Ignition 0 Voltage

P064C

P064C

--

--

Typical Scan Tool Data

Ignition 1 Signal

Circuit

Normal Range

Short to Ground

Open

Short to Voltage

Operating Conditions: Ignition ON

Battery Positive Voltage

Battery Voltage

0 Volts

0 Volts

--

Circuit/System Description

The glow plug control module (GPCM) has the ability to perform internal diagnostics for voltage and output state of the glow plugs. The GPCM will send a message to the engine control module (ECM) to set this DTC.

Conditions for Running the DTC

    • The ignition is ON.
    • DTC P064C runs continuously.

Conditions for Setting the DTC

The GPCM detects a variation between the main battery supply to the GPCM and battery supply to the ECM, or an internal condition for 3 second.

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.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls 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

    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Verification

  1. If you cannot duplicate the conditions, refer to Testing for Intermittent Conditions and Poor Connections .
  2. Engine running, observe the DTC information with a scan tool. DTC P064C should not set.
  3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

  1. Ignition ON, verify the scan tool GPCM Ignition 1 Signal parameter is battery voltage.
  2. If the Ignition 1 Signal parameter is not battery voltage, test the battery positive voltage circuit to the glow plug control module for an open or short to ground. If the circuit tests normal, replace the GPCM.
  3. Ignition OFF, disconnect the X2 harness connector at the GPCM.
  4. Ignition ON, verify that a test lamp illuminates between the ignition 1 voltage circuit and ground.
  5. If the test lamp does not illuminate, test the ignition 1 voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the GPCM.
  6. Ignition ON, verify that a test lamp illuminates between the ignition 0 voltage circuit and ground.
  7. If the test lamp does not illuminate, test the ignition 0 voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the GPCM.
  8. If all circuits test normal, replace the GPCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for GPCM replacement, setup, and programming