U0109
Lost Communication with Fuel Pump Control Module
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Code U0109 means the powertrain control module has lost communication with the Fuel Pump Control Module (FPCM). The FPCM is a relatively modern component that controls fuel pump speed and operation based on commands from the PCM. Instead of the fuel pump running at full speed all the time, the FPCM varies pump speed to match engine demand, improving efficiency and reducing noise. When communication is lost, the fuel pump may not operate at all.
This is a high-severity code because without fuel pump operation, the engine will not run. The classic symptom is an engine that cranks normally but will not start. A quick check is to turn the ignition key to the ON position (without cranking) and listen for the brief whirring sound of the fuel pump pressurizing the system—silence indicates the pump is not running. If the vehicle was running when communication was lost, it may stall suddenly as fuel pressure drops.
Start diagnosis at the FPCM fuse box—a blown fuse is the simplest and cheapest fix. The FPCM connector, typically located near the rear of the vehicle close to the fuel tank, should be inspected for corrosion since this is an exposed location. The CAN bus wiring to the FPCM takes a long route through the vehicle and should be inspected for damage. If the module itself has failed, replacement is moderately priced, but the vehicle will likely need to be towed to a shop since it cannot be driven without fuel delivery.
Severity
Symptoms
- •Engine cranks but will not start—no fuel pump whirring sound heard
- •Vehicle stalls suddenly while driving and will not restart
- •Loss of engine power or hesitation before complete failure
- •Fuel pressure dropping to zero despite a full fuel tank
- •Check Engine Light on, possibly with additional fuel system codes
- •Extended cranking time before engine eventually starts
Likely Causes
The Fuel Pump Control Module requires a reliable 12V power supply and ground. A blown fuse, corroded fusible link, or oxidized ground connection—common failure points—will cause the module to shut down and stop communicating on the CAN bus.
The FPCM wiring runs from the rear of the vehicle (near the fuel tank) to the main CAN bus harness. This long routing exposes it to road debris, moisture, and undercarriage damage that can sever or short the communication wires.
The FPCM controls fuel pump speed and operation. Internal component failure—particularly the power MOSFETs that drive the pump and the CAN transceiver—can cause the module to stop functioning and drop off the network.
The FPCM connector is typically located near the fuel tank, an area prone to moisture, road salt, and debris. Corroded pins can create enough resistance to prevent reliable CAN bus communication.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Check all fuses and fusible links related to the fuel pump circuit
- Inspect the FPCM connector (usually near the fuel tank) for corrosion and clean with electrical contact cleaner
- Verify 12V power and ground at the FPCM connector with a multimeter
- Test CAN bus wiring continuity from the FPCM to the main harness junction
- Replace the Fuel Pump Control Module if all electrical tests pass