This 2004 Ford F250 with a 5.4 liter gas engine came in with the complaint that the engine would occasionally stall. Testing found a code P0231 stored which indicates a problem with voltage to the fuel pump. Studying a wiring diagram showed several things. Number one is that when the fuel pump relay is engaged it supplies power to two different wires. Both dark green with a yellow stripe. One wire goes to the fuel pump via the inertia switch and the other goes to the PCM. If the code P0231 was stored and there was no performance problem with the fuel system the problem could be in the wiring between the fuse box and the PCM. In this case there was a complaint of an intermittent engine stalling condition so that meant the issue was related to the fuel pump relay. The second thing was that the fuel pump relay is built into the fuse box and is not readily serviceable. Time for an inspection.
There are four screws that hold the fuse ox to the underside of the dash. They all have 10 mm heads.
There is a battery wire at the far left end of the fuse box that has to be removed. I recommend disconnecting the battery before doing this. The plastic cap that covers the terminal and stud is a bit of a pain to remove and I used this hooked tool to release the latches. I released the one on the underside first and then the one I am working on in the following picture.
The 10 mm nut that holds the cable to the fuse box stud.
There are multiple harness connectors plugged into the backside of the fuse box assembly. There are several types of latches used to lock the connectors in place. All have latches that have to be depressed first except for one that has a loop on the end that has to be bulled up. It is the one to the far right in the next picture.
The fuse box out and sitting at my work station.
I like to mark the relays so that I can reinstall them in their original locations. I obviously also take a picture so that I know where all of the fuses go. The battery stud has to be removed before separating the plastic case halves. A couple of pocket screwdriver’s can be used to release the case latches and separate the two halves.
The fuel pump relay is the upper on to the right of the circuit board in the next picture.
There were 57 solder joints along the lower edge of the circuit board that had to be unsoldered in order to remove the circuit board from the rest of the fuse box. If you will enlarge the next picture and look closely at the leading corner of the right relay you should be able to see the melted plastic case.
From the backside of the board the heat discoloration can be seen along with a failed solder joint. Five more solder joints to desolder.
In total there were 62 solder joints that had to be unsoldered and then resoldered to complete this repair. I also reflowed and additional 57 solder joints on the mating board.