PCM fuse keeps blowing - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 07-12-2009
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PCM fuse keeps blowing

can someone help with this. i have a 96 b3000 with a 3.0 and my PCM fuse keeps blowing. can some on tell me what the pcm is and where its located. is it what ford calls its cpu or something different. i must have a short somewhere. it did it today in the rain so that is what i am thinking. does anyone know what color wires i should look for when looking for a short. is this a common problem. thanks.
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Old 07-12-2009
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one more thing when it blew my oil gauge was flickering up and down. hope it helps.
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Old 07-12-2009
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Does it blow as soon as you replace it, switch the ignition on, during or after starting the engine or while your driving?
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Old 07-12-2009
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right now it is blowing as soon as i put the fuse in with ignition off. usually it blows while i am driving. it will start sputtering for a few seconds then go dead. today i even tried putting an 80amp fuse in just to get it home and it popped it as soon as i put it in. what is a pcm anyway.
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Old 07-12-2009
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The PCM is the vehicles main Computer. I believe its mounted in the firewall (passengers side) above the AC unit under hood. If the fuse blows as soon as you install a new one, I'd suspect either the PCM Power Relay points are stuck closed (due to short) or the short is between the fuse and the Relay in the power distribution box.

This fuse supplies 12V power to the PCM, fuel pump relay, fuel injectors, purge flow sensor, IAC valve, MAF sensor, EVAP purge valve, EGR vacuum regulator via the PCM Power Relay.

Last edited by Rev; 07-13-2009 at 12:07 AM.
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Old 07-12-2009
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^^^ that about covers it to try and track down a short in the wiring can be a little challenging because of all the wires but all those wires run to the fuse panel first i think so i would check the fuse panel under the hood to make sure all the right fuses are there and if you cant figure it out might have to take it to a dealer. of if you know someone with the same truck see if you can swap the pcms and see if you still have the same problem
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Old 07-13-2009
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the fuses are in the right spots and i dought the pcm is bad. i am pretty sure its just a short somewhere. you are right that there are a LOT of wires to look through and not much room. i may have to tow it home and tear into it. thanks for your input guys.
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Old 07-15-2009
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ok so i tried letting the truck dry out after a few days without rain and its still blowing the pcm fuse. i did notice that the pcm relay clicks when its plugged in so its always hot. i don't really know what that means but i am sure it has something to do with my fuse blowing as soon as i plug it in. BTW this is with the key in the on position. maybe someone can figure this out. thnaks.
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Old 07-15-2009
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The PCM relay is energized in the run and start position. See if it clicks with the ignition off and key removed. If not, remove the relay and try installing a new fuse again and see if it still blows. If it doesn't blow with the relay removed that should rule out the wiring in the distribution box itself.

Has there been any work done on the truck in the last year or two?

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