OBD-II Code U0109 — Lost Communication with Fuel Pump Control Module

What Does This Error Mean?

U0109 means your car's computer has lost communication with the Fuel Pump Control Module. Some modern vehicles — especially GM trucks and SUVs — use a dedicated module to control fuel pump speed and pressure instead of a simple relay. When that module goes silent, the ECM may not command fuel delivery at all. This code can cause a no-start condition or engine stalling. It's one of the more serious communication codes because it directly affects whether the engine runs.

Affected Models

GM trucks and SUVs (Silverado, Sierra, Tahoe, Yukon, Suburban)
Cadillac Escalade
GMC Envoy and Trailblazer
Some Chevrolet Impala and Monte Carlo
Vehicles with returnless fuel systems using electronic fuel pump control

Common Causes

Failed Fuel Pump Driver Module (FPDM) — a small module usually mounted near the fuel tank
Blown fuse supplying power to the fuel pump control module
Corroded or damaged wiring connector at the fuel pump driver module
Chafed or broken wiring in the harness that runs under the vehicle to the rear
Failed fuel pump that has created an overload condition and damaged the control module

How to Fix It

Check the fuse for the fuel pump control module. On GM trucks, there is typically a fuse in the underhood fuse box labeled FUEL PUMP MODULE or FPDM. Replace it if blown and try starting the vehicle.

If the fuse blew, investigate why before just replacing it — a blown fuse often means an overload caused by a failing pump or a wiring short.
Locate the Fuel Pump Driver Module. On most GM trucks it's a small black module attached to the frame rail or inner fender near the fuel tank. Inspect its connector for corrosion, moisture, or damage. Clean and reseat the connector.

The module is exposed to road grime, salt, and water spray. Corrosion at the connector is very common on higher-mileage vehicles.
Inspect the wiring harness running from the engine bay to the rear of the vehicle. Look for any spots where the wires might have chafed against the frame, been pinched by a suspension component, or been damaged by a trailer hitch installation.

Trailer hitch wiring jobs sometimes accidentally damage the fuel pump harness running alongside the frame rails.
Listen for the fuel pump priming when you turn the key to ON without cranking. You should hear a brief hum from near the fuel tank for 2-3 seconds. No sound at all when the key is first turned to ON confirms the pump is not receiving a command.

If you hear the pump prime normally, the module may be reporting intermittent faults rather than a hard failure.
If the module and wiring check out and the code persists, the FPDM likely needs replacement. It's a relatively affordable part ($50-$150). Replace it and see if the code clears. If the new module also triggers U0109, suspect a wiring fault between the ECM and the module.

GM part numbers for the FPDM are well-documented online. Verify the part matches your exact vehicle year and build date.

When to Call a Professional

Fuel pump and fuel system work involves flammable fuel — take fire precautions. The fuel pump driver module is usually located under the vehicle near the fuel tank, which can be difficult to access. If fuel pump replacement is also needed, that job is best done by a professional. Expect $100-$150 for diagnosis and $150-$400 for module replacement, plus separate fuel pump costs if needed.

Frequently Asked Questions

Will my car start with U0109?

Often no — or it may start and stall immediately. If the fuel pump control module isn't communicating, the ECM may not send a run command to the fuel pump at all. Some vehicles will prime the pump with a backup relay as a failsafe, allowing the engine to start, but fuel delivery will be unreliable.

Is U0109 always a module failure?

No — the most common cause is actually a bad wiring connector at the module, not the module itself. Before buying a new FPDM, always clean and inspect the connector thoroughly. Many U0109 codes are resolved by cleaning a corroded connector for less than $5 in parts.

Is U0109 a common GM problem?

Yes — it's one of the more frequently seen GM-specific communication codes. The Fuel Pump Driver Module location (near the rear axle, under the vehicle) exposes it to harsh conditions. There are multiple TSBs for various GM trucks related to FPDM failures and wiring corrosion. Check the NHTSA database or GM owner forums for your specific model year.