Code
P1234
Other
P — Powertrain
Fuel Pump Driver Module Off Line
Views:
UK: 25
EN: 46
RU: 33
AI status
Completed
Completed
100%
Causes
- Blown fuse or faulty fuel pump relay
- FPDM loss of power or ground (open circuit, poor connection, corrosion)
- Damaged or disconnected wiring harness or connector to FPDM
- FPDM internal failure
- Loss of network communication (CAN/LIN) between PCM/ECM and FPDM
- Battery or supply voltage too low
Symptoms
- No crank/no start or extended cranking with no fuel pressure
- Engine stalls or will not maintain idle
- Low or no fuel pressure at rail
- MIL illuminated; stored communication DTCs (U-codes) may appear
- Intermittent loss of fuel pump operation or erratic pump behavior
What to check
- Use a scan tool: read all DTCs, attempt to communicate with FPDM, note freeze frame data
- Check battery voltage (should be ~12–14 V) and connections
- Inspect fuses and fuel pump relay; test/replace if suspect
- Visually inspect FPDM connector and wiring for corrosion, bent pins, damage
- Measure supply voltage at FPDM connector with ignition ON
- Check ground continuity from FPDM ground to chassis/negative battery
Signal parameters
- FPDM supply voltage (pin-dependent): ~11–14 V with ignition ON
- Module ground: continuity to battery negative; resistance typically
- CAN bus (if used): CAN_H ≈ 2.5 V idle, CAN_L ≈ 2.5 V idle; dominant state ~3.5 V / ~1.5 V
- Communication: FPDM should respond to requests from PCM/scan tool; module ID/parameters present
- Control output to pump (if driven by FPDM): PWM 0–100% duty depending on commanded flow, frequency varies by design (tens to hundreds of Hz)
- No communication or repeated timeouts when FPDM is offline
Diagnostic algorithm
- Safety first: relieve fuel system pressure before disconnecting fuel lines, and disconnect battery if instructed by vehicle service procedures.
- Connect a professional scan tool. Record and clear all codes, then attempt to communicate directly with the FPDM. Note whether the module is listed and whether it responds.
- Verify battery voltage ≥12 V with ignition ON. A low supply can prevent module wake-up.
- Inspect fuses and fuel pump relay. Test continuity and replace if blown or suspect.
- Visually inspect FPDM connector and wiring for corrosion, bent pins, water intrusion, or damage. Repair or reseal as needed.
- With ignition ON, measure supply voltage at the FPDM power input connector. If missing, trace and repair the feed (fuse, relay, wiring) back to battery/ignition source.
- Check ground continuity from FPDM ground pin(s) to battery negative. Fix high-resistance or open grounds.
- Check network communication: use a scan tool to monitor CAN/LIN traffic. If no traffic or bus errors, inspect bus wiring, terminations, and related modules (PCM). Repair bus faults.
- If power, ground, and bus are good but no module response, test wiring continuity between PCM and FPDM communication pins. Repair any opens/shorts.
- If wiring and vehicle side circuits are good, bench-test or replace the FPDM. Follow manufacturer programming/relearn procedures after replacement.
- After repairs, clear codes, confirm communication with the FPDM, verify fuel pressure and pump operation, and road-test to ensure problem is resolved.
- If intermittent, reproduce symptom while monitoring voltages and communications to catch transient faults.
Likely causes
- Blown fuse or fuel pump relay (easy to check and common)
- Corroded/loose connector at FPDM or fuel pump (common)
- Open power or ground circuit to FPDM
- CAN bus wiring fault or missing termination preventing communication
- Failed FPDM (requires replacement/testing)
Fault status
Status
Fuel Pump Driver Module Off Line — No communication with FPDM detected. Fuel pump may not operate; check power, ground, connectors, and network communication.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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