Fault code P064C – glow plug control module malfunction

Fault code P064C is called “Glow Plug Control Module (GPCM) Malfunction” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P064C

The OBD-II trouble code P064C is a general code that is defined as “glow plug control module failure”. It is set when the powertrain control module (PCM) detects a failure of the glow plug control module itself.

Fault code P064C – glow plug control module malfunction

This code is only applicable to vehicles with engines operating with compression ignition (diesel engines).

Although diesel engines rely only on compression to ignite the fuel-air mixture, it is very difficult to do so when the engine is cold. That’s why all diesel engines are equipped with glow plugs. These go into the pre-combustion chamber and are designed to facilitate the initial heating of the fuel-air mixture during a cold start.

In modern systems, the glow plugs are controlled by a special control module. Which can determine the electrical resistance of each glow plug.

The advantage of this is that the control module can modulate the current applied to each individual glow plug. Therefore, all glow plugs are heated to the same temperature in the same amount of time.

Each time the ignition is turned on and power is applied to the PCM, several self-tests of the controller are performed. By performing the controller self-tests, the PCM can monitor the serial data sent over the Controller Area Network (CAN) to ensure that the on-board controllers are communicating properly.

The PCM monitors the glow plug control module through dedicated communication circuits, and if any malfunction occurs, prevents effective communication. Therefore, if a problem is detected while monitoring the glow plug control module, code P064C will be stored and the malfunction indicator lamp (MIL) may illuminate.

Symptoms of vehicle malfunctions

The main signal that an error P064C has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The glow plug warning light will light up.
  2. Poor starting of cold engine.
  3. Loud knocking noise, which will be present until engine warms up to operating temperature.
  4. Floating revolutions, as well as attempts to stall at idle when the engine is cold.
  5. A drop in engine power when accelerating the vehicle.
  6. Occurrence of white smoke from the exhaust pipe.
  7. Increased fuel consumption.

Diagnostic code P064C is considered serious because it can cause problems with the engine and vehicle handling. The engine may suddenly stall or become erratic. For this reason, this error must be corrected as soon as possible.

Factors that can cause this error code

The error code P064C can mean that one or more of the following problems have occurred:

  • Glow plug is defective.
  • Glow plug control module is defective.
  • Open or short circuit in wiring.
  • Open or short circuit in CAN circuit.
  • Damaged, corroded wiring or connectors.
  • Blown fuse or fusible link.
  • Defective or damaged glow plug driver.
  • Low battery voltage.
  • Faulty PCM module or programming error.

How to fix or reset OBD-2 code P064C

Some suggested steps for troubleshooting and fix the error code P064C:

  1. Inspect the wiring for damage, abrasions, breaks, and shorts. If the wiring is damaged, repair or replace it.
  2. Disconnect and test each CAN bus pin with a special diagnostic scanner.
  3. Inspect and check the fuse and fusible link.
  4. Check the wiring diagram of the relay and fuse system.
  5. Test and replace the glow plug control module if necessary.
  6. If the problem persists, the PCM may need to be replaced and reprogrammed.

Diagnose and repair of problems

This error is considered a common problem with diesels, regardless of manufacturer. Because of the high amperage required to operate the glow plugs, and their tendency to burn out.

The glow plug control module (GPCM) uses low amperage, so it is less likely to fail. The solenoid is also rarely replaced. When you are dealing with high amperage, even the slightest loosening of the connection will cause arcing and damage the connector.

Connecting the battery

To rule out all possibilities of fault P064C, you should visually inspect the wiring, check the voltage on the battery. You should also check the battery terminals and cables for loose connections.

Make sure that the system voltage corresponds to the value in the manual. The charging system is fully functional and the battery is in good condition, begin the diagnostic procedure.

Wiring Inspection

Inspect the wiring from the PCM to the GPCM. Continue down to the solenoid on the valve cover, from the solenoid to the bus bar, and down to the glow plugs. Look for loose or corroded connectors.

Disconnect the black and green electrical connector from the GPCM. Inspect the connector for squeezed out contacts and corrosion. Using an ohmmeter, check each of the terminals for a ground short. Correct the short circuit if necessary.

Apply dielectric grease to the terminals and reconnect the harness to the GPCM. Inspect the plus wire and GPCM connection on the glow plug solenoid. Make sure all wires are clean and in proper condition.

Inspect the glow plug bus. Check the connection of each wire on the bus and make sure they are clean and free of damage.

Remove the wire from the glow plug and check for a short to the ground. Use an ohmmeter to test the glow plug terminal. The glow plug is out of service if the resistance is not within 0.5 to 2.0 ohms.

Check the resistance in the wiring from the glow plug to the tire. The resistance should also be in the 0.5 to 2.0 range. If not, replace the wire.

Checking the glow plugs

If the wiring check fails and fault P064C still remains, refer to the service manual. Locate where the glow plug diagram is shown. Look at the color and pin number for the GPCM power supply and on to the solenoid.

Check these terminals with a voltmeter as directed. If there is no power to the GPCM, the PCM is defective. If there is voltage to the GPCM, check it from the GPCM to the solenoid. If there is no voltage to the solenoid, replace the GPCM.

On which vehicles does this problem occur most frequently

Fault code P064C can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Ford (Ranger)
  • Mercedes-Benz (Sprinter)
  • Mitsubishi
  • Skoda
  • Volkswagen (Passat, Tiguan)

Fault code P064C can sometimes be found with other errors. The most common are the following: P0670, P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P0679.


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