U0109 — Lost communication with fuel-pump control module A

U0109 concerns missing messages from fuel-pump control module A. It is not a direct measurement of fuel pressure and does not prove that the pump has failed. First separate a controller that cannot communicate from a pump or fuel-supply fault diagnosed by other tests.

Affected system: Control-module communication

Symptoms

• The engine may crank without starting, with fuel-system or engine warnings.
• The fuel-pump controller may be absent from a full-system scan.

Possible causes

• Missing controller power/ground, including the applicable fuse or supply path.
• Network wiring or connector faults; a controller fault remains possible after those paths are verified.

What to check

• Save a full scan and identify which modules store U0109, then attempt direct fuel-pump controller access.
• Verify battery condition, the relevant fuses/relays and the controller's documented power and grounds before condemning the pump.
• If several units are offline, diagnose their shared network path; if only this controller is missing, focus on its branch and connectors.
• If controller communication is restored but no-start remains, continue the separate OEM pump-command and fuel-pressure diagnosis. Do not bridge relays or open pressurised fuel lines as a shortcut.
• Verify both repeated controller communication and the original starting complaint after repair. Module location and connector tests depend on the exact vehicle.

Also written as: U0109-00, U010900, UO109 (some scan tools add the fault-type byte, e.g. -00).