U0109 Lost Communication With Fuel Pump Control Module (FPCM)

U0109 Lost Communication With Fuel Pump Control Module (FPCM)

OBD-II DTC Datasheet

Lost Communication With Fuel Pump Control Module (FPCM)

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 that the fuel pump control module (FPCM) 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.

The FPCM controls the fuel pump based on information received from the powertrain control module (PCM). If the information is not received, the fuel pump will not work. These modules are more commonly used in gasoline engines, although their use is increasing in recent diesel engines.

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 U0109 engine code may include:

• Malfunction Indicator Light (MIL) is on
• The car starts but does not move
• If the engine is running: vibrations; Lack of power; Poor performance; Misfire in cylinders (rough operation)

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 U0109 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 U0109, try contacting the FPCM. If you can access the codes from the FPCM module, then code U0109 is either intermittent or a memory code. If the GPCM module cannot be contacted, then code U0109 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 FPCM on this vehicle. Check all grounds for the FPCM. Locate ground anchorage 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 U0109 returns or you can contact the FPCM module. If no code is returned or communication with the FPCM is restored, 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 FPCM connector. Disconnect the negative battery cable before disconnecting the connector on the FPCM. 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 plugging the connectors back into the FPCM. You will need access to a digital volt-ohmmeter (DVOM). Make sure you have power and ground on the FPCM. Access the wiring diagram and determine where the primary power and ground supplies go into the FPCM. Reconnect the battery before proceeding with the FPCM still disconnected. Connect the red wire of your voltmeter to each B + (battery voltage) power source going into the connector on the FPCM module, and the black wire of your voltmeter to a good ground (if unsure, the negative pole of the battery always works). You should see the battery voltage reading. Make sure you have a good reason. Connect the red wire from the voltmeter to battery positive (B +) and the black wire to each ground. Once again, you should see the battery voltage every time you plug it in. If not, troubleshoot 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 AFCM, 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 U0109, the only thing to do is to seek help from a trained automotive diagnostician, as this will indicate a faulty FPCM. Some FPCMs must be programmed or calibrated for the vehicle in order to install correctly.

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