The damage was even easier to see from the relay side of the board.

Once I had it opened it was easy to see the damage. I took the back cover off of the fuse block and started disassembling it. I carefully removed all fuses and relays from the fuse block and laid them out in the order removed. You can see the battery terminal post on the lower left edge. I have my finger in the pull handle for it. There are connectors on the top where testing was done and on the edge. There is only one bolt that holds this fuse block in place. I have pictures of that at the end of this post. There is a battery feed cable that also has to be disconnected on the rear edge of the fuse box. With all of this testing I knew without a doubt that the fuel pump relay that is part of the interior fuse box was faulty.ĭisconnect the battery first before removing the fuse block. This told me that the pcm was using a ground to energize the fuel pump relay coil. When the ignition is turned on the reading was near zero volts and after a few seconds it went to battery voltage. It is in the lower right hand corner of the twelve cavity connector just below the connector that I am backprobing in the picture above. The next step was to locate the light blue/orange wire in cavity #12 of the C270B connector. I checked fuse #34 with the key on and it had power and was good so that eliminated a faulty pcm relay and related wiring. This told me that the fuel pump, inertia switch and related wiring were all okay. Since my backprobe wire is part of a fused jumper wire, I connected battery voltage to the circuit and started the vehicle. I placed a jumper wire into the cavity to backprobe the circuit, no volts. The wiring diagrams stated that the fuel pump relay output wire was dark green/yellow and it was located in cavity 3 of connector C270K. My next test would involve locating the output circuit from the relay. I did some reading and found that there are five internal, non serviceable relays inside the fuse block. Since my wiring diagrams stated the relay was located in the fuse box, but did not give a specific position, I looked in the owners manual for more info. There is a black plastic cover that has to be pulled off of the actual fuse box. Pull the edge loose at the firewall end and pivot the cover back. There are a couple of covers that have to be removed.

I decided to go to the interior fuse box, where my wiring diagrams, stated the fuel pump relay and fuse are located. A quick check found no fuel pressure and a code P0231 (low voltage on fuel pump monitor circuit). This 2003 Ford Expedition came in with a no run condition.

2003 ford expedition fuel pump location