2003 F150 4.6L Supercrew- August of 2012 took it in because i had been having trouble starting it which had been getting progressively worse over a couple months. After replacing fuel pump, fuel regulator, wiring pigtail, crankshaft sensor and running multiple test the last resort was the computer and that seem to fix the problem. Now 1 year and 10 months later i'm having the same problem. Some times it cranks right up and others it just won't crank at all. All tests of fuel system and electrical come back fine. So were guessing another bad ECM but what the heck is causing the ECM to go bad? Very frustrating!!

 

A leaking windshield would do it

 

That's the gem. The PCM is under the hood.

 

Crap my bad I got confused

 

Have you tried a new key? I have seen them where the pats is having a hard time detecting the key and then it gets diagnosed as pcm. Seems to fix it then the issue comes back. The keys do have batteries in them if i recall correctly.

 

It's going to be damn near impossible to diagnose this online. But just as IBD pointed out the GEM module is underneath the windshield. I believe it's short for general electric module. Here's a link on what electrical components it controls: http://www.explorerforum.com/forums/....php?p=1725290

I think the best approach would be to determine which electrical functions are not working and then try to isolate which "brain" does all of those functions. Although something else could be going on too.

I have no idea!

 

I'm with carcrazygts2. It may be a malfunction with the PATS. Although, I don't think the keys have batteries. They have an RFID chip in them that a coil in the ignition lock cylinder reads by passing power around the key. I would get a new key programmed for the PATS to read (must be done by professional) then install a bypass under the dash which contains the new key. Then you'll have to get a standard, non chipped, key to crank it. Had trouble with my PATS on my 00 and this cured it. Good luck though.

 

What makes you conclude that your ECM is Bad? If replacing the sensor will fix the issue then your PRIMARY WIRING or HUGE WIRE HARNESS is the one causing the repeat Failure.

TOO MUCH RESISTANCE in the wiring will build up heat causing electrical component & sensors to fail.
More heat = More Resistance

Best example. If the wire connected to your alternator has too much resistance it will make the alternator works harder. More Resistance will cause bigger voltage drop. The harder it works will make the wiring hotter causing more resistance & more drop in voltage which will surely cause the alternator to fail. Replacing the alternator without replacing the wire with huge resistance will surely cause another failure. Electrical Sensors is using voltage as their language.

 

Try another key.

 

Some of the early gen keys acually had a tiny watch battery in them. My 96 Cobra had one.