2003 Ford F-350 Superduty with 6.0L PSD 4x4 - 120,000 miles with no major issues so far.

Last week I was driving at highway speed and the engine just shut down and would not crank again (all electrics appeared to work except for the starting circuit). I took it to the dealer and they found that the fuse for the PCM was blown. Replaced fuse, test drove and let run in shop all day finally blew fuse as I was there to pick it up. let it cool down and put a new fuse in an ran fine for another day or so then shut down again. Went through 4 other fuses (fuse blew as soon as ignition was switched on) and then let cool down another 20 or so minutes and then started ok and made it to my destination. Has anyone else had experience with the fuse for the pcm blowing. I will try to see if I can get codes off of it later this week since the dealer seemed not to know where to start troubleshooting. I am assuming that my pcm may be going bad, since It works fine when it cools down.

Also had a strange gremlin hit in the ac system- when I switch from 2x4 to 4x4 the ac changes from blowing out the dash vent to the defroster. Not sure if this is related.

Thanks in advance
TC

 

Which fuse? Fuse 2.22 20amp? More info is needed.

As for the other issue, sounds like you have a vacuum supply problem. Your 4x4 uses vacuum to apply the hubs, when your a/c loses the vacuum supply it needs to move the blend doors it defaults to the defrost setting.

 

It is actually a 30 amp fuse in the fuse box under the console.

 

Per the wiring diagram that wire runs from the central fuse junction box to the ignition switch. Assuming you don't have a remote start I would check the wiring to the ignition switch. Other than that you might suspect the FICM since it also powers the FICM in the run position and the FICM uses alot of power.

 

I do have a remote start, I believe it is part of the Viper alarm system. Could this be an issue with the remote start?

 

Most definitely, I would put it back to stock if you are able and see if it reoccurs. Usually there is some sort of computer to go along with aftermarket remote starts and of course it ties into the ignition switch, I have seen these cause some weird issues.

 

Ok, Thanks for the info I will disconnect it tomorrow and see what happens.

 

Hello PC6flyer, did you solve the problem with your fuse blowing, I have the same problem and not sure how to fix it.

 

The shop here found a broken wire in the wiring harness on the engine in addition to the fuse panel being shorted out.

The wiring harness had been rubbing against an exhaust manifold bolt or something in that area. With a little wiring repair and beefing up all is good now.

 

This sounds freakishly similar to what is happening to me right now....

https://www.ford-trucks.com/forums/8...me-please.html

I'm going to check my fuse right now.......