CAN network

U0109 — Lost Communication with Fuel Pump Control Module

Severity: high Drive with care, to a shop

What U0109 means

The engine control module (PCM/ECM) talks to the fuel pump control module (FPCM) over the CAN bus and uses those messages to command fuel delivery. U0109 sets when the FPCM stops responding or its messages are corrupted. Without that link, the pump may run incorrectly or not at all.

Symptoms

  • Check Engine light on
  • Engine cranks but will not start
  • Intermittent stalling while driving
  • Rough running or hesitation
  • Reduced power under acceleration
  • No fuel pump hum when the ignition is turned on

Possible causes

  1. Open, shorted or corroded CAN bus wiring or connectors
  2. Faulty fuel pump control module (FPCM)
  3. Blown fuse or poor power or ground supply to the FPCM
  4. Corrosion at the in-tank fuel pump module connector
  5. Failed fuel pump module assembly
  6. Faulty engine control module (uncommon)

How to diagnose

  1. Scan all modules and save freeze frame data; note other U codes and which modules are not responding
  2. Check the fuses and relays for the fuel pump and FPCM circuit
  3. Turn the ignition on and listen for the pump to prime for a couple of seconds
  4. Inspect the FPCM and fuel pump module connectors for water, corrosion and heat damage
  5. Measure supply voltage and ground resistance at the FPCM connector
  6. Test the CAN bus: resistance between CAN-H and CAN-L (about 60 ohms with power off) and wiring continuity
  7. Wiggle the harness with a scan tool connected to find intermittent opens
  8. Only then test the FPCM and ECM, ideally by swapping in a known good unit

Common fixes

  • Replace the blown fuse and restore power or ground to the module
  • Repair or replace damaged CAN wiring and connectors
  • Replace the fuel pump control module and program it as required
  • Replace the fuel pump module assembly if it has failed
  • Replace or reflash the ECM only after wiring and module tests are complete

Questions and answers

What does U0109 mean?

It means the engine computer has lost CAN communication with the fuel pump control module. The cause is more often wiring, power or connectors than the modules themselves.

Can I drive with code U0109?

It is not advisable. Fuel delivery can cut out and the engine may stall at any time, which is dangerous in traffic. Drive only as far as needed to get it repaired.

Why won't my car start with U0109?

If the engine computer can't see the fuel pump module, it may not command the pump on. The starter spins the engine but no fuel reaches the rail.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.