Code
P1238
LINCOLN
P — Powertrain
Fuel Pump Secondary Circuit Fault
Views:
UK: 20
EN: 31
RU: 25
AI status
Completed
Completed
100%
Causes
- Open, short, or high-resistance wiring in the fuel pump secondary circuit
- Corroded or loose connector at the fuel pump, fuel pump driver module (FPDM), or PCM
- Faulty fuel pump driver module (FPDM) or internal pump driver
- Faulty fuel pump motor (internal short or intermittent)
- Faulty PCM or PCM output driver (less common)
- Faulty relay, blown fuse, or poor battery/ground connection
Symptoms
- Engine cranks but will not start, or starts then stalls
- No fuel pressure or low/erratic fuel pressure under cranking or run
- Fuel pump only runs intermittently or not at all
- Check Engine Light (MIL) illuminated with P1238 stored
- Possible electrical smell or blown fuse if shorted
What to check
- Retrieve and record freeze frame and live data with a scan tool (fuel pump commanded status, fuel pressure, battery voltage)
- Visual inspection of fuel pump connector, wiring harness, and FPDM for damage or corrosion
- Check fuel pump fuse(s) and relay operation
- Verify battery voltage and main chassis/engine grounds
- Measure voltage at fuel pump connector during key ON (prime) and while cranking
- Measure fuel pump current draw with an appropriate clamp meter or inline ammeter
Signal parameters
- Key ON (prime): battery voltage (approx. 11.5–13.5 V) at pump supply if primary circuit intact
- PCM/FPDM command: ground-switched or PWM control — signal should switch between ~0 V (on) and battery voltage (off) as commanded
- Fuel pump current draw (typical): roughly 4–15 A depending on vehicle and pump; significantly higher or near zero indicates fault
- Pump winding resistance (cold): usually low, often under 2 ohms (consult vehicle-specific spec)
- Fuel pressure: should rise to specification during prime/crank (varies by engine — consult model/service data)
Diagnostic algorithm
- Connect a capable scan tool, read and record fault codes, freeze frame, and live data (fuel pump command, fuel pressure, battery voltage).
- Perform a visual inspection of the fuel tank area, pump module, wiring harness, connectors, and FPDM for damage, corrosion, or loose connections.
- Verify fuses and relay(s) for the fuel pump circuit. Replace or substitute relay if necessary and re-test.
- With key ON (do not start), measure voltage at the fuel pump supply terminal. If supply is present but pump does not run, suspect pump or FPDM. If supply missing, trace back to relay/primary feed.
- Command the pump ON using the scan tool while monitoring voltage and current at the pump. Note whether the PCM/FPDM is commanding and whether the pump responds.
- Measure pump current draw during operation. High current indicates shorted/weak motor; near-zero indicates open circuit or failed driver.
- Check continuity and resistance of pump secondary wiring (power/ground/driver circuits) from connector back to FPDM/PCM. Repair any opens or high resistance.
- Inspect and test ground connections for the pump and FPDM; clean and tighten as required.
- If wiring and connectors are good and pump current/voltage are abnormal, swap or bench-test the pump and/or replace the FPDM per service manual procedures. Re-scan for codes after repairs.
- If FPDM replacement does not resolve and wiring checks are good, evaluate PCM output driver and replace only after confirming PCM fault with factory procedures.
Likely causes
- Connector corrosion or damaged wiring between the FPDM and pump
- Failed FPDM causing unpredictable secondary circuit behavior
- Fuel pump motor drawing excessive current (partial short) or intermittent open
- Poor engine/chassis ground at pump or module
- Intermittent PCM command output due to internal fault or low battery voltage
Fault status
Status
The PCM has detected an abnormal condition in the fuel pump secondary (driver) circuit. This may be caused by open/short/high resistance in wiring, a failed fuel pump driver module or pump motor, poor grounds, or intermittent PCM control. Investigation of wiring, connectors, pump operation and module outputs is required.
Repair difficulty: Medium
Diagnostic time: 1.5-3 hours
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