OBD-II trouble code
U0109: Lost Communication with Fuel Pump Control Module
A module on the network can no longer hear from the fuel pump control module. Often a power, ground, or wiring fault — and because the module regulates fuel delivery, the engine may run poorly, stall, or fail to start.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $100 – $1,100
- DIY difficulty
- Shop recommended
What does U0109 mean?
U0109 is set when another module on the vehicle's communication network — usually the engine computer — stops receiving messages from the fuel pump control module. On many modern vehicles the fuel pump is not switched simply on or off; a dedicated fuel pump control module varies pump speed to maintain the correct fuel pressure for current demand, and it reports its status back over the network. When the network loses contact with that module, U0109 records the dropout.
The causes follow the familiar communication-code pattern. The fuel pump control module may have lost power or ground through a blown fuse, corroded ground, or failed relay. The CAN wiring or connector at the module can be damaged or corroded — and the module is often mounted in an exposed location, such as near the fuel tank or under the vehicle, where moisture and road debris take a toll. The module's internal communication circuitry can fail, or another module on the bus can disrupt communication for everyone. Low system voltage from a weak battery or charging fault can also cause intermittent dropouts.
Because fuel delivery depends on this module, the symptoms are usually significant. The engine may crank but not start, start and then stall, run rough or lose power under load, or hesitate as fuel pressure becomes unreliable. The check engine light comes on, and there are often companion fuel-pressure or driveability codes. Since an engine that can't be reliably fueled is both a driveability and a safety concern — it may quit at any time — U0109 warrants prompt diagnosis rather than continued driving.
Common causes
- Blown power or ground fuse for the fuel pump control module
- Corroded or loose ground at the module
- Damaged CAN wiring to the fuel pump control module
- Corroded or backed-out terminals at the module connector
- Moisture or road-debris damage at the module's exposed location
- Failed internal communication circuitry in the module
- Another module on the bus disrupting network communication
- Low system voltage from a weak battery or charging fault
Symptoms
- Engine cranks but won't start
- Engine starts then stalls, or stalls while driving
- Rough running, hesitation, or power loss under load
- Check engine light on, often with fuel-pressure or driveability codes
- Scan tool can't communicate with the fuel pump control module specifically
- Symptoms may be intermittent with a marginal connection
- Other U-codes stored in modules that depend on fuel-system data
Diagnostic steps
- 1.Scan all modules; confirm the fuel pump control module is the one that's unreachable while others respond.
- 2.Check the module's power and ground fuses and the relevant relays.
- 3.Inspect the module ground point and connector for corrosion, looseness, and moisture intrusion at its mounting location.
- 4.Measure CAN-High and CAN-Low at the module connector (rest near 2.5 volts) and verify continuity back to the bus.
- 5.Test the battery and charging system, since low voltage can cause intermittent communication loss.
- 6.If power, ground, and wiring are good but the module still won't communicate, the module itself is the likely failure and will need replacement and programming.
Repair cost
$100 – $1,100
A blown fuse, corroded ground, or connector repair is the cheapest fix at $100-$300 once located. Wiring repair runs $200-$600. Diagnostic time commonly adds $150-$300. Fuel pump control module replacement is the most expensive outcome at $350-$1,100 including programming, and is a last resort after cheaper causes are eliminated. Costs rise when the module is integrated with the pump assembly and the tank must be dropped.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.