P1238 on Ford: How to Diagnose & Fix
Manufacturer-Specific Fuel/Injector System Fault
1 Ford model · 1 documented issue · 1 critical · $90-$450 repair
On Ford vehicles, P1238 (manufacturer-specific fuel/injector system fault) is most often reported on the 1999-2008 Ford F-150 as Corroded Fuel Pump Driver Module Sets Fuel Pump Secondary Circuit Fault ($90-$450 repair). Diagnose the codes in the right order. If P1233 is stored with P1238, chase P1233 first — that code means the module has lost power or ground, and fixing it often clears the secondary-circuit fault too. Rated critical: F-150 Corroded Fuel Pump Driver Module Sets Fuel Pump Secondary Circuit Fault. Each section below gives the symptoms, how to confirm the cause, the fix, parts and sources for that model.
Common causes of P1238 (all vehicles)
- Fuel pump circuit, relay, or driver fault (Ford)
- Faulty or open fuel injector / injector circuit (cylinder-specific, VW)
- Wiring, connector, or ground problems in the fuel circuit
- Mechanical injector failure (some Toyota diesels)
- Fuel pump or fuel delivery weakness
- Faulty PCM/ECM driver
- Corroded or loose electrical connections
P1238 on Ford by model: symptoms, diagnosis and fix
On the Ford F-150 the fuel pump is not switched by a simple relay — it is speed-controlled by a Fuel Pump Driver Module (FPDM) that the PCM commands over a duty-cycle line. The FPDM monitors its own output side to the in-tank pump, and when it sees an open, short or out-of-range condition in that secondary circuit it reports the fault back to the PCM, which stores P1238 (Fuel Pump Secondary Circuit Fault). Ford stores this code alongside its siblings P1233 (FPDM disabled or offline) and P1237, and on this truck the three usually have the same root cause. The dominant failure is the module itself rather than the wiring. Ford bolted the aluminum-cased FPDM directly to the steel frame crossmember above the spare tire — the most exposed, salt-blasted spot under the truck. Dissimilar metals plus road salt and standing water produce galvanic corrosion that eats the aluminum case, cracks it open and lets moisture onto the circuit board. The board then throws intermittent secondary-circuit faults before it fails outright. Salt Belt trucks fail at dramatically higher rates than Sun Belt trucks, and the pattern is worst on the 2004-2008 generation, though the earlier FPDM-equipped trucks fail the same way. Drivers usually notice an intermittent problem long before a hard failure: the check engine light comes on, the engine cranks but takes several tries to catch, or it stalls at a stop and restarts a minute later. Because the pump is being commanded at the wrong speed, some owners also see a lean-condition or low fuel pressure code (P0087, P0191) logged in the same session. Eventually the truck simply cranks and never starts, with no fuel pressure at the rail and no pump prime audible at key-on. Owners frequently replace the in-tank fuel pump first — an expensive tank-drop — only to have the code return within days, because the pump was never the problem.
Common Symptoms
- Check engine light with fuel pump circuit codes
- Extended cranking before the engine catches
- Intermittent stalling that clears after a restart
- No-start with no fuel pump prime at key-on
- No fuel pressure at the rail
- Fault returns after replacing the in-tank fuel pump
How to Fix
Diagnose the codes in the right order. If P1233 is stored with P1238, chase P1233 first — that code means the module has lost power or ground, and fixing it often clears the secondary-circuit fault too. Then lower the spare tire and physically inspect the FPDM on the frame crossmember. A case that is white, chalky, swollen, cracked or weeping is the answer; you rarely need further testing. Confirm by back-probing the module for battery voltage on the power feed, a good chassis ground, and the PCM duty-cycle command at key-on, then check for pump drive output on the secondary side. If command is present and output is not, the module is bad. If the module output is good, the fault is downstream — inspect the harness along the frame rail and the connector at the tank for green corrosion and chafing, and check the in-tank pump's own connector before condemning the pump. The repair is a new FPDM, and it is one of the easiest jobs on the truck: two bolts on the crossmember, typically under 30 minutes with hand tools once you have the spare down. The hardest part is breaking the rusted fasteners loose. Critically, do not bolt the new module flat against bare steel again — use the rubber standoffs or spacer kit that ships with the OEM part (Ford 4L3Z-9D370-A on the later trucks) or an aftermarket kit such as Dorman 590-001, so the aluminum case is isolated from the frame, and coat the mounting hardware and the connector with dielectric grease. Skipping the standoffs is the single most common reason a replacement module fails again in two or three winters. Repair any corroded harness sections with soldered, heat-shrunk splices rather than crimp butt connectors, which wick moisture in that location. Clear codes and verify pump prime at key-on and a full 30-minute drive with no return of the fault. Parts run roughly $50-$170 depending on OEM versus aftermarket; dealer labor on top puts a shop repair in the low-to-mid hundreds, while a DIY fix is under $100 of parts. Ford never issued a recall for the corroding module, so this is an owner-paid repair.
Looking for P1238 on a different make?
View P1238 across all makes →Frequently asked questions
What does P1238 mean on a Ford?
P1238 stands for "Manufacturer-Specific Fuel/Injector System Fault." P1238 is a manufacturer-specific powertrain code whose definition varies by maker, so it should be confirmed against model-specific data. Reported meanings include a fuel pump circuit/relay fault (Ford), a mechanical injector failure on some Toyota diesels, and a cylinder 2 injector circuit (open) fault on some Volkswagen/Audi applications. In general it points to a fuel-delivery or fuel-injector problem that can cause hard starting, stalling, misfire, and reduced power. On Ford it is documented across 1 model: F-150.
How do I diagnose P1238 on a Ford F-150?
Diagnose the codes in the right order. If P1233 is stored with P1238, chase P1233 first — that code means the module has lost power or ground, and fixing it often clears the secondary-circuit fault too. Then lower the spare tire and physically inspect the FPDM on the frame crossmember. Published repair guidance and available estimates are in the F-150 section on this page.
What causes P1238 on Ford vehicles?
Documented causes on Ford: Corroded Fuel Pump Driver Module Sets Fuel Pump Secondary Circuit Fault. Generic causes of P1238: Fuel pump circuit, relay, or driver fault (Ford), Faulty or open fuel injector / injector circuit (cylinder-specific, VW), Wiring, connector, or ground problems in the fuel circuit, Mechanical injector failure (some Toyota diesels).
How much does it cost to fix P1238 on a Ford?
Published repair estimates on Ford range from $90 to $450 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.