Fault code P1635 – a step-by-step guide to diagnosing and fixing it

Error code P1635 is displayed and the check engine light is on - what does this mean?

The DTC P1635 is a manufacturer-specific fault code that is recognized by the OBD system and indicates a problem with the fuel pump voltage supply or the fuel pump relay. This fault code mainly occurs in Ford vehicles and indicates a fault in the electrical circuit of the fuel pump.

What causes can this fault code have?

• Defective fuel pump relay
• Damaged fuel pump fuse
• Corroded or loose plug connections on the fuel tank
• Defective fuel pump
• Broken cable connections in the fuel pump circuit
• Faulty ground wire of the fuel pump
• Defective engine control unit (PCM)
• Oxidized contacts in the fuse box

What symptoms occur in parallel with fault code P1635?

• Starting problems: The vehicle is difficult or impossible to start because the fuel pump is not working properly. Engine misfires: Irregular engine running or sudden stalling of the engine while driving. Power loss: Significantly reduced engine power, especially when accelerating or under load. Lack of fuel: The engine is not receiving enough fuel, which leads to jerky driving. Check engine light: The check engine light remains permanently activated.

How can the problem with error code P1635 be rectified?

• Repairing EOBD error code P1635 requires a systematic approach to identify the defective component.
• Check the fuel pump relay and replace if necessary - locate the relay in the fuse box, replace with a working relay or test with a multimeter
• Check and replace the fuel pump fuse - check the corresponding fuse in the engine compartment fuse box and replace with a new fuse of the same amperage if it blows
• Clean and repair electrical connections on the fuel tank - disconnect all plug connections on the tank module, clean with contact spray and reconnect firmly
• Replace the fuel pump completely - if the pump is defective, remove the entire tank module and replace it with a new original part
• Repair the fuel pump wiring harness - locate damaged cables between the fuse box and tank, repair severed areas or replace the entire wiring harness
• Have the engine control unit diagnosed and programmed - In the event of a PCM defect, visit a professional workshop for a control unit test and, if necessary, replacement with subsequent programming