Vehicle: F-150 Trucks 2004-2005. (Note: This article may apply to other Ford trucks that are wired the same, but these models are the ones we have verified.)
Symptom: Intermittent no-start. May or may not set codes. When the trucks don’t start, the scanner will not communicate, the throttle control motor (TCM) and sometimes the charge motion control (CMC) valve will make a loud clicking/knocking sound or cycle with just key on. Replacing these parts does not change the symptoms in any way.
Diagnosis and Testing: The diagnostics normally lead to checking for vehicle power on the large gauge red wire to the injectors, powertrain control module (PCM) and all PCM controlled outputs. It must be full battery voltage whenever the key is on. We recommend using a headlamp bulb to load the circuit. If the voltage is erratic or low, check the PCM power relay for corrosion or other problems.
If there is another relay in the central junction box (CJB), also known as interior fuse panel, with the same part number, the relays can be swapped to see if the symptoms change. If swapping the relays doesn’t fix the problem, check the 15A fuse #34 in the CJB. Pull the fuse out and look at the element. Testing the fuse with a test light or logic probe may not find the problem. Replace the fuse with a known good fuse if needed and verify the symptom is gone.
In most cases, corrosion of the fuel pump driver module (FPDM) causes an internal short. The fuse will take the short for a while, and will distort and limit current flow before it blows. The FPDM is mounted to the rear cross member above the spare tire. Perform a good visual inspection of the FPDM and replace it if it shows any signs of corrosion.
The Fix: When you buy a new FPDM from Ford, it will include two studs that, when installed correctly, hold the FPDM away from the steel cross member to eliminate the corrosion issue. Ford recommends grinding any corrosion off of the cross member, and coating it with grease to help slow down the corrosion process.
Service data provided by Identifix Inc. For more information, visit the company’s Web site at www.identifix.com.
