U0109: Lost Communication With Fuel Pump Control Module A
Do not keep driving
Depending on the vehicle the engine may stop or refuse to start, or it may drive completely normally while the pump runs at full output all the time.
Either way, get it looked at rather than continuing. If it is currently the version that drives normally, the risk is that it becomes the other version without warning, and stopping in moving traffic is the outcome to avoid.
The module usually lives low down at the back of the car near the fuel tank, which is the worst place on the vehicle for water and road salt — so its connector and wiring are the first things to check, ahead of the module or the pump.
What this code means
The fuel pump control module has stopped being heard from. The general reasoning is at U0100.
A fuel pump control module exists to vary pump speed rather than run it flat out — the arrangement described at P2539, where delivering only what is needed saves energy and stops the fuel being warmed by surplus circulation. When the module goes quiet, the pump's behaviour depends on how the design fails, and both directions matter.
- Fails off, and the engine stops or will not start. Unambiguous, and it will not be mistaken for anything else.
- Fails to full output, which is the more interesting case: the car drives perfectly. Rail pressure is high, the pump runs at maximum continuously, the fuel warms and the pump wears faster than it should. Nothing is wrong to drive and something is being consumed, which is the shape this corpus keeps finding.
Marked not to be driven because the first outcome can arrive at any moment and stopping in traffic is the consequence.
The module is frequently mounted low at the rear of the vehicle, near the tank, which is the worst place for water and salt — and its connector is a routine finding.
Likely causes
Start here
- Corroded or loose connector · easy
- Water ingress into connector · moderate
- Damaged data bus wiring · moderate
- Failed power or earth supply to the module · moderate
Less common
- Blown fuse or failed supply · easy
- Faulty fuel pump control module · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about U0109.