Description of DTC code U0109

The communication that the vehicle's control modules constantly maintain is through a circuit known as controller area network bus communications, or simply CAN (Control Area Network) bus. Without this communication protocol, the modules can't exchange the information necessary for proper operation.

One of these controllers is the Fuel Pump Control Module, which is responsible for the operation of the fuel pump taking into consideration the information sent from the PCM (Powertrain Control Module). This data is used to adjust and regulate an important component of the fuel system, in order to ensure a good fuel supply. Generally, this type of module is integrated into vehicles with gasoline engines, although its use in diesel engines has increased considerably.

When the U0109 OBDII fault code is set, it means that the Fuel Pump Control Module has not been able to establish communication with another controller that has requested the respective information.

How does the U0109 Generic Fault Code work?

This is a generic DTC that usually appears in several brands and models of vehicles, which includes some like Dodge, Ram, Chevrolet, Ford, GMC, and VW. This code means that the Fuel Pump Control Module (FPCM) and other control modules on the vehicle do not communicate with each other. Without the CAN bus, the control modules are unable to communicate and their scan tool might not get information from the vehicle, depending on the circuitry involved.

The FPCM controls the fuel pump based on information received from the PCM. If the information is not received, the fuel pump will not operate. These modules are usually employed on gasoline engines, although their use on newer diesel engines is increasing.

Troubleshooting steps may vary by manufacturer, type of communication system, number of wires, and colors of communication system wires.

Symptoms of fault code U0109

  • Check Engine light is on.
  • The vehicle starts but does not run.
  • The engine is unstable in operation.
  • Lack of engine power.

Causes of OBD2 U0109

The reasons for setting the U0109 OBD2 diagnostic code are as follows:

  • CAN bus wiring or connectors may be faulty.
  • Fuel Pump Control Module wiring may be in poor condition.
  • The Fuel Pump Control Module may be faulty.

Possible solutions of the DTC code U0109

The steps to troubleshoot the DTC U0109 OBDII code are as follows:

  • Consult the Technical Service Bulletins.
  • Inspect the wiring of the positive circuit, negative circuit, and CAN bus ground signal. If you find any of these damaged by corrosion, burns, or wear, make the necessary repairs.
  • Check for damage to the wiring and connectors related to the Fuel Pump Control Module. If you detect common deficiencies, proceed with the respective corrections.
  • If even after performing the above-mentioned repairs you still get the code U0109, it is necessary to verify that no module is damaged.
  • If your vehicle manufacturer does not use the CAN bus for connection between the PCM and AFCM, you should establish the correct voltages for this connection circuit.

If all tests pass and the communication is still not possible, or you were unable to clear DTC U0109, the only thing to do is to find help from a trained automotive tester, as this will indicate the FPCM specific fault. Some FPCMs must be programmed or calibrated for the vehicle to install correctly.

Codes related to U0109

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