U0106 Lost Communication with Glow Plug Control Module (GPCM)

OBD-II DTC Datasheet

Lost Communication With Glow Plug Control Module (GPCM)

What does this mean?

This is a generic communications DTC that applies to most makes and models of vehicles, including but not limited to Dodge, Ram, Chevrolet, Ford, GMC, and VW. This code means the glow plug control module (GPCM) and other control modules on the vehicle are not communicating with each other.

The circuitry most commonly used for communication is known as Controller Area Bus communication, or simply the CAN bus. Without this CAN bus, control modules cannot communicate and your scan tool may not receive information from the vehicle, depending on which circuit is involved.

Without this communication scheme, the GPCM cannot receive information from the engine / powertrain control module (ECM / PCM) computer about how and when to use the glow plugs. Without this information, the GPCM will not operate the glow plugs.

Troubleshooting steps may vary depending on the manufacturer, the type of communication system, the number of wires, and the colors of the wires in the communication system.

symptoms

Symptoms of a U0106 engine code may include:

Malfunction Indicator Light (MIL) is on
Longer than usual cranking time when the engine is cold
Possible knock / premature ignition (spark knock) if glow plugs are fired when not needed

reasons

Usually the reason for installing this code is:

Open in CAN + bus circuit
Open in the CAN bus - electrical circuit
Short circuit to power in any CAN bus circuit
Short to ground in any CAN bus circuit
Rarely - the control module is faulty

Diagnostic and repair procedures

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

First, look for other DTCs. If any of these are bus communication or battery / ignition related, diagnose them first. Misdiagnosis is known to occur if you diagnose the U0106 code before any of the major codes are thoroughly diagnosed and rejected.

If your scan tool can access trouble codes and the only code you are getting from other modules is U0106, try contacting the GPCM. If you can access the codes from the GPCM, then code U0106 is either intermittent or a memory code. If the GPCM module cannot be contacted, then code U0106 set by other modules is active and the problem already exists.

The most common failure is a loss of power or ground.

Check all fuses supplying the GPCM on this vehicle. Check all grounds for the GPCM. Locate grounding attachment points on the vehicle and make sure these connections are clean and secure. If necessary, remove them, take a small wire bristle brush and baking soda / water solution and clean each one, both the connector and the place where it connects.

If any repairs have been made, clear the DTCs from all modules that set the code in memory and see if U0106 returns or you can contact the GPCM module. If no code is returned, or communication with the GPCM is restored, then the problem is most likely a fuse / connection issue.

If the code returns, look for the CAN bus communication connections on your specific vehicle, especially the GPCM connector. Disconnect the negative battery cable before disconnecting the connector on the GPCM. Once detected, visually inspect the connectors and wiring. Look for scratches, scuffs, exposed wires, burn marks, or molten plastic. Disconnect the connectors and carefully inspect the terminals (metal parts) inside the connectors. See if they look burnt or have a green tint indicating corrosion. If you need to clean the terminals, use an electrical contact cleaner and a plastic bristle brush. Allow to dry and apply dielectric silicone grease where the terminals touch.

Perform these few voltage checks before connecting the connectors back to the GPCM. You will need access to a digital volt/ohmmeter (DVOM). Make sure you have power and ground on the GPCM. Access the wiring diagram and determine where the main power and ground supplies enter the GPCM. Connect the battery before continuing with the GPCM disabled. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply plugged into the GPCM connector, and the black lead of your voltmeter to a good ground (if unsure, battery negative always works). You should see the battery voltage reading. Make sure you have a good reason. Connect the red lead of the voltmeter to the battery positive (B+) and the black lead to each ground circuit. Once again, you should see the battery voltage every time you connect. If not, repair the power or ground circuit.

Then check the two communication circuits. Locate CAN C+ (or HSCAN+) and CAN C- (or HSCAN - circuit). With the black wire of the voltmeter connected to a good ground, connect the red wire to CAN C+. With the key on and engine off, you should see about 2.6 volts with little fluctuation. Then connect the red wire of the voltmeter to the CAN C- circuit. You should see about 2.4 volts with little fluctuation.

If your vehicle manufacturer does not use the CAN bus for communication between the PCM and the GPCM, you need to determine the appropriate voltages for this communication circuit.

If all tests pass and communication is still not possible, or you were unable to clear DTC U0106, the only thing that can be done is to seek help from a trained automotive diagnostician, as this will point to a faulty GPCM. Some GPCM modules may need to be programmed or calibrated for the vehicle in order to install correctly.

Related DTC discussions

U0106 Generic, lost contact with glow plugThis is my first time and I try to avoid dealer service. I have a GMC Serria 2006 HD 2500 pickup and get the generic code U0106; communication with the glow plug is lost. Any thoughts. Duramax Diesel 6.6, 80,000 miles Thank you ...

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