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DTC codes / U01xx · Lost communication with a control module / U0109

U0109Lost Communication With Fuel Pump Control Module

U0109 means the engine control module (ECM) or another primary controller has stopped receiving the periodic status messages it expects from the fuel pump control module over the controller area network (CAN) bus. The computer has detected a communication timeout, not necessarily a failed fuel pump, so the fault lies in the module, its power supply, or the data network linking it to the rest of the vehicle.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaLost communication with a control module

Symptoms you may notice

  • Illuminated check engine light or service vehicle soon message with no other obvious change in behavior
  • Crank but no start condition because the fuel pump control module is not being commanded to run the pump
  • Engine stalls shortly after starting or refuses to restart once warm
  • Reduced engine power or limp mode with an electronic throttle warning on some vehicles
  • Fuel gauge reading incorrectly or dropping to empty if the pump module shares gauge data
  • Often no symptoms besides the warning light when the fault is intermittent or stored during a brief network glitch

Common causes, most likely first

  1. Corroded, loose, or damaged electrical connector at the fuel pump control module, especially in areas exposed to road spray and salt
  2. Broken, chafed, or open-circuit wiring in the CAN bus or module power/ground circuits between the ECM and the fuel pump control module
  3. Failed fuel pump control module internal electronics, often from heat, vibration, or water intrusion
  4. Blown fuse or faulty relay in the fuel pump control module power supply circuit
  5. Poor ground connection at the module mounting point or chassis ground stud
  6. A second module on the same CAN segment pulling the bus down and disrupting all communication
  7. Low battery voltage or a failing charging system causing modules to drop offline intermittently

How to diagnose and fix it

  1. Scan all modules for communication codes and record which controllers are online to confirm the fuel pump control module is the only one missing
  2. Inspect the fuel pump control module connector for corrosion, pushed pins, or water intrusion and clean or repair as needed
  3. Check the module power and ground circuits with a multimeter under load, including fuses, relays, and ground studs
  4. Measure CAN bus resistance and voltage at the module connector to rule out an open or shorted data line
  5. Perform a wiggle test on the harness while watching live module communication status to catch intermittent faults
  6. Substitute a known-good module of the same part number only after confirming power, ground, and bus integrity
  7. Clear codes and verify communication returns and remains stable through a full drive cycle before releasing the vehicle

Communication faults are rarely the module itself

  • A U0109 is stored by the module that lost contact, so the fault may be in the wiring between modules rather than inside the fuel pump control module.
  • Water intrusion into the module connector or housing is a common hidden cause on vehicles where the module is mounted low on the chassis or near the fuel tank.
  • A weak battery or failing alternator can cause multiple modules to drop offline and set communication codes that disappear after charging system repair.
  • Replacing the fuel pump control module without checking the CAN bus can leave the same code present if another module is shorting the network.
  • Some vehicles require the new module to be programmed or configured to the vehicle, so a used module may not communicate correctly even if it is functional.

Can I keep driving with U0109?

If the engine starts and runs normally, you can drive cautiously to a repair shop, but avoid long trips and heavy load because the fuel pump may stop without warning. If the engine cranks but does not start or stalls repeatedly, do not continue driving and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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