Code U0109 on the 2021 Ram 1500 indicates lost communication with the fuel pump control module. This module manages fuel pump operation, controlling pump speed based on engine demand and providing fuel pressure data to other systems.
Fuel Pump Module Operation
Modern fuel pump control modules do more than simply turn the pump on and off. They vary pump speed based on engine load, monitor fuel pressure, and communicate fuel system status to the ECM. The Ram 1500's module integrates with the vehicle's returnless fuel system for precise pressure control.
Starting and Running Issues
With U0109 active, the engine may crank but not start due to lack of fuel pressure. If the vehicle does start, it may run poorly or stall under load when fuel demand increases. The ECM may command reduced power to protect the engine from lean fuel conditions. Warning lights illuminate on the dashboard.
Diagnostic Investigation
The fuel pump module on the Ram 1500 is typically located near or integrated with the fuel pump assembly in the tank. Check the wiring connector at the top of the fuel tank first - this connector is exposed to road debris and moisture. Verify power and ground supplies reach the module. A failing fuel pump can draw excessive current and damage the control module.
Repair Path
Wiring and connector issues are common due to the exposed location. If the module has failed, it may be integrated with the fuel pump assembly, requiring fuel tank removal for service. Stellantis diagnostic tools are required for module programming after replacement.