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Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 48357
Experience:  16 years experience
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I just purchased a 2000 F150, 4.6L ext cab 4x4. It had a

Customer Question

I just purchased a 2000 F150, 4.6L ext cab 4x4. It had a check engine light, so I read the code and it's a P1633 for keep alive memory low. I checked the fuses in the dash, and PCM fuse #2 was broken, so I replaced it. When I did, the theft light, battery light, and airbag light all came on. I tried to start the truck, and got nothing. I pulled the fuse, and the dash returned to normal, and the truck would start. When I replaced the fuse with the truck running, when I turned the key to the off position, the truck kept running. I pulled the fuse and could turn the truck off. The only other thing I noticed was the radio fuse was broken, and when I replaced it, it immediately popped. The stock radio is in the truck. I'm more concerned about the PCM issue. Where should I start? I'm a decent mechanic, but electrical is not my forte!
Submitted: 1 year ago.
Category: Ford
Expert:  Chris (aka- Moose) replied 1 year ago.

Welcome, I'm Chris (aka Moose). Experts aren't employees / agents of Just Answer. We are independent service providers using the Site to sell their Expert knowledge to Customers. I strive to provide EXCELLENT 5 STAR service, let me know what's needed from me so your pleased.

I can honestly say I have never seen or heard anything like that. It sure sounds to me like the PCM is faulty in this case but I am not 100% sure. Do you own a scan tool that can see which codes are stored with the fuse in place?

Customer: replied 1 year ago.
I do. I was thinking PCM as well, but haven't seen that much over the years. I'll see what codes I get tomorrow.
Expert:  Chris (aka- Moose) replied 1 year ago.


Customer: replied 1 year ago.
Moose, I'm getting no additional codes with the fuse in. I just made a short video. I started the truck with the fuse out, and all was well except for the check engine light with the same P1633 code. I turned off the truck, and restarted. When I inserted the PCM fuse, the airbag light was the only one that came on. When I turned the key off, the truck stayed running, just like yesterday.
Expert:  Chris (aka- Moose) replied 1 year ago.

Can you look at the wiring around the fuse box and ignition switch to see if anything looks out of place or if someone has added something aftermarket?

Customer: replied 1 year ago.
Man, this truck is driving me nuts. No evidence of any aftermarket items. Same issue with the PCM fuse. In addition to blowing the radio fuse upon putting a new one in, I found the brake light switch was disconnected. I plugged it in, and checked and had no brake lights. I put in a fuse in the #15 spot for the stop lamps (which has other things on it), and it immediately popped that fuse too. Want to buy a POS cheap? lol
Expert:  Chris (aka- Moose) replied 1 year ago.

Some of these issues are for sure wire shorts to ground causing immediate fuse failure when replaced. Do you need the wire diagrams for these circuits

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Customer: replied 1 year ago.
That may help, but I'm not sure where to begin, even with those. I don't know if these are all related, or if it's just an electrical nightmare.
Customer: replied 1 year ago.
I don't think I'd be chasing those 2 shorts separately from each other, as well as the PCM thing. I would think they have a common issue, like a short in the fuse box itself, or at a single point somewhere. What would you think for a first move?
Expert:  Chris (aka- Moose) replied 1 year ago.

My first choice would be to replace the PCM, though that is based on not performing any diag yet.

Do you understand wire diagrams and wire testing with a multimeter?

Customer: replied 1 year ago.
I would say I'm on a novice level. I just can't see it being 3 separate problems. It's possible, sure, but a common source seems more likely to me.
Expert:  Chris (aka- Moose) replied 1 year ago.

We can pick one issue and diagnose it and hope it address every issue if you choose. Fuse 15 would be the easiest to diagnose. Let me know what you would like to do?