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.
It sounds exactly like a relay issue. I do not know if I really should mention this or not. The initial problem is not with the relay. It is a solder joint problem for the relay. If caught early enough, all that really needs to be done is to just resolder the connection. If you look closely at the solder joints for the relay you should see a black ring in the solder joint around the relay terminal. Very early in the failure it will be a slightly darker shade of silver/gray. As the problem worsens the ring will darken and get wider. The ring or crack initially will be less than half the diameter of a human hair. Sadly that is enough to produce a pedestrian situation.
Sparky,
Thanks for the quick response! Although the 2006 is different your post is the only thing that has helped me begin troubleshooting that the dealership couldn’t even do. I have already replaced a fuel pump that didn’t fix anything based on the dealership diagnostic.
I do have an update after troubleshooting this more. Let me know if i am understanding things correctly as the issue is starting to look like the relay issue again from the original post of yours.
If I ground a test light and test the fuse #12 (Fuel Pump) with the key in the run position it stays on steady. This tells me that I have power to the relay. When I plug this test light in to the same slot as the Dark Green / Yellow wire, it has no light when the pump has not been able to prime. If I leave that hooked up and turn the ignition back and forth, I see the light blink every time for a second. When it finally hits a point where the fuel pump kicks on and primes, the light stays on that time instead of blinking and going out.
If I jumper the Dark Green / Yellow to a hot fuse that has power on ignition, the car starts and the fuel pump primes every time!!! Earlier testing I was trying to use the jumper to hear the pump come on after I had the key in the on position but did not try leaving the jumper in and re-trying the ignition.
Does this confirm the issue is with the relay? Or is more testing in order before I order a relay and solder it in?
Thanks again!!!
-Greg
First of all your 2006 system is very different from the 2003 that I posted about. Luckily the dark green/yellow wire is in the same place with the same function. Battery power is sent out on it to the FPDM and arrives on the white wire. The color changes at the inertia switch. Once there, nothing happens until the PCM sends a pulse width modulated signal on the light blue/orange wire. The PCM monitors the FPDM operation via a signal sent back to it on the light blue/red wire. Since there are no codes there are two different diagnostic paths to consider. Either the problem lies between the FPDM and the fuel pump or there is a condition present in the PCM data that is disabling the need for fuel pressure. Basic voltage testing can be done at the FPDM and fuel pump with a good voltmeter. Data will need to be examined with a scan tool that has access to the appropriate data. Assuming the engineers put it in there to start with.
Sparky,
One other thing on my 2006 Ford Expedition issue, I did as you said and jumpered the Dark Green and Yellow wire with the ignition on, but the fuel pump did not come on.
Thanks again.
-Greg
Sparky,
You seem to be the most knowledgeable person on this topic, so I hope you have an idea for me.
I have an 06 Ford Expedition XLT that is experiencing very similar issues as described in the other posts.
Here is my issue:
When I turn the ignition to the on, but not crank stage, the fuel pump will prime about once out of 15 tries and is random. If the fuel pump primes, then the car runs as it should, but if it does not prime it does not run.
Here is what I have done so far:
1) Changed the Fuel Pump (No Change)
2) Changed the FPDM (No Change)
3) Bypassed Inertia Switch (No Change)
4) Removed and inspected fuse box as instructed in your blog. (No issues there, all joints look good and no burnt spots of any kind.)
Is there anything else you can point me to on this? Pulling my hair out and the dealership has no idea what the issue is. There is no codes on the ODB2.
Any help would be appreciated.
Thanks!
-Greg