PCM problem, please help ASAP!
Thread Starter
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New User
Joined: Jan 2012
Posts: 11
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No I do not, I get no idiot lights and the truck won't start. It has to be my PCM. This all happened the day I installed my power programmer. Come to find out the company sent me one for a manual transmission (my truck is not a manual). So I pulled the power programmer off and sent it back. Being the smart guy that I am, I did not disconnect my battery while installing the power programmer. Needless to say, my truck does not start now! Lesson learned!
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
Did you check the fuse with a multi meter or test light? Sometimes it is hard to tell whether the fuse is blown (although with these Max fuses it's usually fairly apparent). And yes there is a relay under the hood for the PCM. Just swap it with any of the others (the horn relay is a good one since it is easy to test - push the horn). They're all the same.
Thread Starter
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New User
Joined: Jan 2012
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I replaced the fuse and relay with new ones and my truck still has all the same symptoms (no "WTS" light, no engines lights come on, and it won't start). The engine definitely cranks over like it would like to start, but nothing. What other possibilities before I take it to a shop?
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
The only thing I can suggest at this point is to check the wiring harness that goes into the back of the PCM where it sticks through the firewall. Make sure it is tight (there is a bolt that holds it into the PCM). Also check the red wire in that harness. It should get 12V with the key in the "run" position. If not, you have a wiring problem. If it does, then I am thinking that you have another bad PCM. You replaced the PCM with what? A new one? And you replaced the PCM and not the IDM right? IDM is on the fender under the hood, PCM sticks through the firewall from inside the cab.
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Thread Starter
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New User
Joined: Jan 2012
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Alright, thank you for all of your help. I will check all of that. I went to autozone and got a refurbished PCM. Lol, yes I am sure that it is the PCM that I replaced. Another thing, the ford dealership said it might not start after I install the new one cause it might need to be flashed. Is that true?
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
Alright, thank you for all of your help. I will check all of that. I went to autozone and got a refurbished PCM. Lol, yes I am sure that it is the PCM that I replaced. Another thing, the ford dealership said it might not start after I install the new one cause it might need to be flashed. Is that true?
I don't think the new PCM should need to be flashed. I would think it would have a version flashed to it when you buy it. Did it have a version code on it when you bought it that matches one of the codes on the previous page?
There is also a diode in the circuit that supplies power to the PCM. You might check that as well while you have the DVOM out. If you don't have a DVOM with a diode setting on it, just check it for continuity. If it conducts, you're probably alright.
Posting Guru
Joined: Aug 2004
Posts: 2,417
Likes: 4
From: Braham MN
I know this is prolly a super rare occurance but I had a guy bring me a 95 with the same symptoms, no wts light, no start, no smoke. After swapping pcm and idm with good know ones i had nothing. All fuses were good, relays worked but the pcm would never get power. The glow plug regulator never clicked either, so for some odd reason I unhooked the EBP sensor and heard the gpr click. Turns out the EBPS was shorted out and was pulling the voltage down low enough that none of the sensor/relay circuits would work but wouldn't blow a fuse. It was very frustrating.
Again, prolly a super rare deal but worth a shot. Turn the key on and onhook one sensor at a time, see if anything changes.
Again, prolly a super rare deal but worth a shot. Turn the key on and onhook one sensor at a time, see if anything changes.
Postmaster
Joined: Sep 2007
Posts: 4,195
Likes: 6
From: Medford Oregon
Good point and troubleshooting tip. You are correct, if any of the sensors the use VREF or +5 volts from the PMC are shorted then the PCM is inoperative, I forgot that. IIRC the ones that use it are MAP, EBPS, ICP and BARO. CPS also uses it however truck won't start with it unplugged, however you should get dash idiot lights and GPR operation.
