U0109

Universal

Lost Communication With Fuel Pump Control Module

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The vehicle has detected that one or more control modules cannot communicate with the fuel pump control module over the vehicle network. That module helps control fuel-pump operation. Depending on the vehicle and whether the fault is active, the engine may run normally, lose power, stall, or fail to start. This code alone does not prove the fuel pump control module needs replacement.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the engine stalls, loses power, or will not restart, pull over safely and arrange assistance rather than continuing to drive in traffic. If the vehicle runs normally, have the fault checked promptly and watch for changes. Do not work around moving parts or exposed wiring.

Common Symptoms

  • The engine may crank but not start if the communication fault prevents fuel-pump operation.
  • The engine may stall or lose power if fuel delivery is interrupted while driving.
  • The vehicle may start and run normally if the fault is intermittent or does not affect current fuel-pump operation.
  • A warning light or related communication message may appear, depending on the vehicle.

Common Causes

  • A loose, damaged, corroded, or poorly connected module connector or wiring may interrupt power, ground, or network communication.
  • A weak battery, charging problem, or other unstable power supply may disrupt communication.
  • A fault elsewhere on the vehicle network may prevent messages from reaching the fuel pump control module.
  • The fuel pump control module may have an internal fault, but this should be confirmed through testing before replacement.

Diagnostic Steps

  1. Note whether the engine starts, runs, stalls, or shows other warnings; these details help distinguish an intermittent communication issue from one affecting fuel-pump operation.
  2. Check the battery condition and look for obvious loose or damaged battery connections, since unstable vehicle voltage can disrupt module communication.
  3. With the vehicle safely parked and the ignition off, visually inspect accessible wiring and connectors related to the fuel pump control system for looseness or visible damage. Do not disconnect components unless the vehicle's service information says it is safe.
  4. Check relevant fuses using the vehicle owner's manual. Replace a blown fuse only with the specified type and rating; if it blows again, have the cause diagnosed.
  5. If you have a suitable scan tool, check for codes in other modules and record them before clearing anything. Related codes can help identify a broader network or power issue.
  6. Arrange professional diagnosis if the problem persists, the engine stalls, or the module cannot be reached with a scan tool. Avoid probing network wiring without the correct vehicle-specific procedure.

When to Call a Professional

A technician can scan all modules for related communication codes, check whether the fault is active or stored, and verify the fuel pump control module's power, ground, connectors, and network communication using vehicle-specific service information. Several network or power-supply faults can cause this code, so confirm the cause before replacing a module.

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Commonly Asked Questions

Does U0109 prove the fuel pump control module has failed?

No. The code reports lost communication, which can result from a wiring, connector, power, ground, or network fault as well as an internal module problem. Testing is needed to identify the cause.

Can I drive with U0109?

It depends on how the vehicle behaves. If it runs normally, arrange diagnosis promptly and monitor it closely. If it stalls, loses power, or will not restart, stop driving when safe and arrange assistance.

Why does the engine still run if this code is present?

The fault may be intermittent or may not currently prevent the fuel pump from operating. Vehicle designs differ, so normal operation does not rule out a communication problem.

What should be checked before replacing a module?

Check related codes, module power and ground, connectors, wiring, and network communication using service information for the specific vehicle. A communication code alone is not a parts diagnosis.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.