Blown PCM Fuse

Tiny
SNOOPY11895
  • 1997 FORD F-150

I have a 1997 Ford F-150 with 132,000 miles, 4.2L 6 cylinder engine. My truck keeps blowing the PCM fuse when I engage the ignition. The relay is fine. It used to finally turn over after changing the fuse 4 times, but now it will not turn over at all. I also have a check engine light that says the upstream O2 sensor is bad. I have no idea where to even begin with this problem.

I tested f24, f30, and the MAF red wire. All three have power with the ignition in the on position.

Any advice would be greatly appreciated.

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Wednesday, May 9th, 2007 AT 7:37 PM

4 Replies

Tiny
2CARPROS KEN
  • ADMIN
  • 11,698 POSTS

It sounds like you have a system power wire that is pinched or has rubbed through to ground. Here some guides and some wiring diagrams so we can do some testing and get the problem fixed.

https://www.2carpros.com/articles/how-to-check-wiring

What fuse # are you replacing and is it in the eng. Comp? When you say "engage the ignition" is that from OFF to RUN or RUN to START? Does your anti-theft light blink rapidly when it fails to start? Why do you think the PCM relay is fine? Do you have an aftermarket anti-theft or remote start system installed. Is this a man. Or auto trans? Your full and complete answers are needed to accurately diag. Your concern.

The fuse number is 24, and it is in the engine compartment. I believe the PCM relay is good because it does not look blown/bad. What I mean by engage the engine is from run to start. I have no anti-theft (factory or aftermarket) The truck is an automatic.

Please recheck the relay as well.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Please let us know what you find.

Cheers, Ken

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Tuesday, September 19th, 2017 AT 11:22 AM
Tiny
SATURNTECH9
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Just to add to this one I just had a 2002 mercury mountaineer that suddenly blew the ecm fuse which feed power to the heated o2 sensors a lot of the emission controls etc. It turned out the wires on the passenger side o2 sensor wires had shorted to the exhaust pipe up high where it was hard to see.I put a bulb across the the fuse that was blowing with the key in the run position. It was brightly lit I had someone watch the light while I moved wires around the light was flashing when I moved the shorted out wire that's how I found it.

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Tuesday, September 19th, 2017 AT 11:39 PM
Tiny
2CARPROS KEN
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Good find!

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Wednesday, September 20th, 2017 AT 11:26 AM
Tiny
SATURNTECH9
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That's a great way to find short circuits.

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Wednesday, September 20th, 2017 AT 1:24 PM

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