U0109 Lost Communication with Fuel Pump Control Module
The U0109 code indicates that the Powertrain Control Module (PCM) has lost serial data communication with the Fuel Pump Control Module (FPCM) over the high-speed CAN bus. This loss prevents the PCM from sending speed/pressure commands to the fuel pump or receiving feedback on its status, typically causing the fuel system to shut down as a safety measure.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Open or short circuit in the CAN bus (High/Low) wiring to the FPCM
- Internal failure of the Fuel Pump Control Module (FPCM)
- Loss of battery power (B+) or ground (GND) at the FPCM
- Damaged, loose, or corroded FPCM connector
- Faulty Powertrain Control Module (PCM) – rare
- Low system voltage (weak battery or failing alternator) affecting the CAN network
3. Symptoms You Will Notice
- Engine cranks but does not start
- Check Engine Light illuminated
- Fuel pump may not operate
- Possible stalling or no-start condition
4. Step-by-Step Diagnosis
Scan for all stored codes and freeze frame data
Inspect FPCM connector for damage, corrosion, or loose pins
Check battery voltage and charging system; ensure at least 12.6V
Test CAN bus wiring (CAN High and CAN Low) for continuity, shorts, or resistance
Verify power and ground circuits at the FPCM
If all else passes, suspect FPCM or PCM failure; perform module communication test
5. Frequently Asked Questions
Is it safe to drive?▼
No, this is a critical fault. The fuel system may be disabled, causing the engine to stall or not start. Driving is not recommended.
How much does it cost to fix?▼
Repair costs vary widely: from $100–$200 for a wiring repair to $400–$800+ for FPCM replacement, plus diagnostic fees.