This 2003 Ford Expedition came in with a no run condition. A quick check found no fuel pressure and a code P0231 (low voltage on fuel pump monitor circuit). I decided to go to the interior fuse box, where my wiring diagrams, stated the fuel pump relay and fuse are located. There are a couple of covers that have to be removed.
Pull the edge loose at the firewall end and pivot the cover back.
There is a black plastic cover that has to be pulled off of the actual fuse box.
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. No luck there. I did some reading and found that there are five internal, non serviceable relays inside the fuse block. My next test would involve locating the output circuit from the relay. 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. I placed a jumper wire into the cavity to backprobe the circuit, no volts. Since my backprobe wire is part of a fused jumper wire, I connected battery voltage to the circuit and started the vehicle. This told me that the fuel pump, inertia switch and related wiring were all okay.
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. The next step was to locate the light blue/orange wire in cavity #12 of the C270B connector. 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. When the ignition is turned on the reading was near zero volts and after a few seconds it went to battery voltage. This told me that the pcm was using a ground to energize the fuel pump relay coil. 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.
Disconnect the battery first before removing the fuse block. There is a battery feed cable that also has to be disconnected on the rear edge of the fuse box. It is located under a cover. I have pictures of that at the end of this post. There is only one bolt that holds this fuse block in place.
I unplugged all of the wiring. There are connectors on the top where testing was done and on the edge. Above and below the mounting bolt.
In the rear.
This connector has a slide mechanism. I have my finger in the pull handle for it.
The fuse block removed from the vehicle. You can see the battery terminal post on the lower left edge.
I carefully removed all fuses and relays from the fuse block and laid them out in the order removed.
I took the back cover off of the fuse block and started disassembling it.
Once I had it opened it was easy to see the damage. Slightly right of center.
The damage was even easier to see from the relay side of the board. I feel fairly confident that if this problem would have been caught soon enough, the solder joint could have been repaired or a new relay installed (if one could have been located).
The old fuse block on the left and the new one on the right.
I plugged everything back in and bolted the fuse block in place.
This is the end of the battery cable that I referred to earlier.
The cover for the battery stud on the fuse block.
I put all of the covers back on, cleared the codes and test drove the vehicle. This one is done.
This repair will generally apply to Ford and Lincoln full sized trucks and suv’s in the same years//body style. Check diagrams and component locators before jumping any circuits, as I did.
The discoloration would be an indicator of heat build up from worn contacts inside the relay. The original fuel pump may have been part of the overheating situation. Since I cannot inspect it personally, you will need to use your own best judgement or ask your mechanic to inspect the relay and circuit board for you. When the solder joint is starting to fail there will be a very fine black line in a circle pattern, in the solder that surrounds the relay terminal.
Sparky,
Thanks for this thorough diagnosis of the problem. I had fuel pressure issues with my 03 Expedition. It died twice but than started the next day. I thought it was fuel pump, took it to a mechanic and he agreed. He replaced the fuel pump, truck ran great, but died a few days later. Mechanic said the new fuel pump went bad. So he replaced it again for no charge. But while test driving it, the truck died again. So he said he didn’t know what it was. So I did some research and found this article. Testing showed no voltage on the Green/Yellow wire so I figured it was the relay like your article showed. I took the CJB out and took it apart and there is no scorching on the solder points, they look intact. The relay has no scorching or melting either. But the back of the circuit board is discolored a bit for that relay and around it. Could that discoloration mean the circuit board is bad? Maybe cause the relay is drawing too much power? OR is my problem somewhere else?
Thanks,
Bob
Sparky, I just wanted to say thanks a million for the information you posted about the fuel pump issue with the Ford Expedition. To make a long story short, I’ve been dealing with issue for over 6 months with my 05 Expedition Limited. I’ve changed out a few parts, did hours of trouble shooting between working, working and more working. Your post took me right to the issue with my truck. The third hard wired relay on the circuit board was the problem. It wasn’t burned out on the board but the relay would sometimes work. I replaced the fuse box which by the way comes with everything on it. My truck runs great. Thank you again and my God over whelm you with his blessing.
Just wanted to thank you for your knowledge. I ended up taking out my fusebox an solder the back of that 303 relay. Install the fusebox. And the expo cranked an drove it all with no problems. Thank you once again, I pray that God will continue bless the works of yur hands an to increase your knowledget. Stay blessed.
A good rule of thumb is the same size wire that you are jumping to. If I remember correctly the dark green/yellow wire was 16 or 14 gauge. My jumper wire is twelve gauge with an inline fuse that needs to be rated the same as the fuel pump fuse.