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 P0640: Intake Air (IA) Heater Control Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

IA Heater Temperature Signal

--

P154D

P154D

IA Heater Command 2

P154B

P154B

P154B

IA Heater Voltage Signal

P154B

P154B

P154B

IA Heater Command 1

P154B

P154B

P0640

IA Heater Current Signal

P154C

P154C

P154C

IA Heater Feedback Signal

P154A

P154A

P154A

IA Heater Battery Positive Voltage

P154B

P154B

--

Circuit/System Description

The intake air (IA) heater is located in the air inlet tube and is used to warm the incoming air to aid in starting the engine and for proper cylinder combustion. The glow plug control module (GPCM) will command the IA heater ON when the engine coolant temperature is below 40°C (104°F). The power to the IA heater is supplied by the battery positive voltage circuit. The IA heater is connected to the GPCM by the following circuits:

    • The IA heater temperature signal circuit
    • The IA heater command 1 circuit
    • The IA heater command 2 circuit
    • The IA heater voltage signal circuit
    • The IA heater current signal circuit
    • The IA heater feedback signal circuit

If there is a fault on any of these circuits, a DTC will set.

Conditions for Running the DTC

    • The IA heater is commanded OFF.
    •  DTC P0640 runs continuously when the above condition is met.

Conditions for Setting the DTC

The digital response signal is high and the command 2 signal is activated.

Action Taken When the DTC Sets

DTC P0640 is a Type B DTC.

Conditions for Clearing the DTC

DTC P0640 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. Ensure that the IA heater Command 1 CKT Short to Voltage parameter displays OK.
  2. Ensure that the IA heater can be commanded ON.
  3. Engine running, observe the DTC information with a scan tool. DTC P0640 should not set.
  4. 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

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

  1. Disconnect the IA heater
  2. Turn ON the ignition. Test the IA heater command 1 circuit terminal 2 for less than 12 volts.
  3. If greater than 12 volts, test the command 1 circuit for a short to voltage. If the circuit tests normal, replace the glow plug control module.
  4. If the command 1 circuit tests normal, replace the IA heater.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References for GPCM replacement, setup, and programming
    •  Intake Air Heater Replacement