VIN 6

DTC P0640

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC P0640
- Intake Air (IA) Heater Control Circuit

Diagnostic Fault Information





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 ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ensure that the IA heater Cmd 1 CKT Status 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.

• 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.

3. If the command 1 circuit tests normal, replace the IA heater.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Intake Air Heater Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for GPCM replacement, setup, and programming