how can I tell if the computer (PCM) is bad - F150online Forums



how can I tell if the computer (PCM) is bad

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Old 11-01-2009, 01:22 AM
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how can I tell if the computer (PCM) is bad

what the title says

my truck has no spark and the rpms do not register when cranking the truck so I replaced the Crank sensor and still the same thing, I know fuel is going to the cylinders but the thing is just not sparking and it I am almost positive it is not the coil packs because they could not have gone out overnight(literally)

but anyways since I am almost sure it is the computer (unless there is a relay) how can I tell if it is really that without buying a new one
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Old 11-01-2009, 10:54 AM
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Does the CEL come on at ignition power on? If not, the PCM probably isn't getting power.

Check fuses F24 & F30 in the under-hood box and the PCM Power relay.

If either fuse is blown, there are common reasons.
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Old 11-01-2009, 12:02 PM
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Some years ago, I had a similar problem. Fuses and everything was okay, but there was a fuseable link that went out making the PCM not get any power. It would crank all day, just never start.
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Old 11-01-2009, 12:22 PM
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@kingfish where was the fusible link

@projectsho what number is the pcm relay
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Old 11-01-2009, 01:52 PM
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Quote:
Originally Posted by Stephen87 View Post
@kingfish where was the fusible link

@projectsho what number is the pcm relay
Sorry, don't know. As the vehicle was under warranty, I just let the dealer deal with it. Just got the explanation.
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Old 11-01-2009, 04:33 PM
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hmm I guess I will try and get it out of the dealer
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Old 11-01-2009, 04:42 PM
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I dont have any idea but it may be a last resort fuse actually inside the CPU.
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Old 11-01-2009, 06:01 PM
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did you check all your fuses?
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Old 11-01-2009, 06:09 PM
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Check the fuses and relays under the hood of the truck. The pcm relay is one of the three larger ones ( the others are the fuel pump and horn) and you can swap them around to check them.
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Old 11-01-2009, 06:41 PM
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Well I started to check all of the fuses and I started inside and a 30 amp fuse (numbered 30 on the little chart thing in the fuse panel) was blown so I replaced it and I am charging my battery and hopping that that will have been the problem
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Old 11-01-2009, 09:21 PM
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SUCCESS!!!!

turns out it was that fuse...man that sucks that my truck was brought down by something smaller than a nickle

however my truck still does not start up immediately when I turn the key what happens is the starter relay clicks but the starter does not turn I may need to pull my starter and clean it(it looks to have a lot of oil on it) and hopefully that will solve my problem
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Old 11-01-2009, 09:21 PM
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(DOUBLE POST, Stupid computer)

Last edited by Stephen87; 11-01-2009 at 09:33 PM.
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