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.
20 amp. The same size as the factory fuse (#34) that normally protects that circuit.
I was just wondering what size fuse did you use in your jumper wire?
Where to begin…turns out, I couldn’t figure out why the truck wasn’t running. Took it in to the shop, and here’s what we found: 1. Fuel pump had a blown out hose (the brownish opaque corrugated one). Looked like it just burst, and we’re not exactly sure why. 2. I had sprayed starting fluid directly in the throttle body, twice, trying to confirm spark. Apparently, not a good idea with this motor, as it pooled up, fumed up, and contributed to the problem. Good thing is, it apparently broke up a bunch of carbon that was sitting inside. An inspection of one of the plugs revealed a significantly fouled plug, with a messed up gap. So, on to #3. 3. Opened her up, removing plugs, which revealed they were all fouled. Plug 4 (i think), was completely rusted. He got them all out w/o breaking any. Intake manifold gasket had 3 areas where the seal was blown. Cleaned intake, put it all together, new gaskets, new plugs, a couple of new boots, new fuel pump, and she’s up and running, albeit a significant expense later. Thank you to Sparky for helping me eliminate the fuse box as the cause of the no start. Who could have guessed that the fuel pump was getting power, but just pumping fuel through a broken hose. I guess it’s a good thing that we caught the issue with the plugs now, since the rusted one was probably on the verge of being thrown, and according to the mechanic, is the toughest one to get to when it happens. The joys of buying a used truck and not knowing the exact maintenance history.
Using a voltmeter check for power at the red/lt green wire at one of the coil harness connectors with the key on.
Thanks Sparky. I guess I was wrong when I said I had spark. I did the original test yesterday, spraying a bit of starting fluid in the throttle body. It ran for a second, then cut off. Well, today, I tried again, and it won’t start at all with fluid. So I’m thinking I actually don’t have spark. I checked the two fuses on the fuse box that look like they deal with ignition (104 which is 10a, and another that I can’t recall the number, but it was a 30a), and they look OK. I guess I could test at the coils, but for all 8 to be bad would be improbable. Is there something I’m not aware of that controls the power to all eight coils?