Bad PCM?
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Junior User
Joined: May 2008
Posts: 69
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From: Friendswood, TX
Bad PCM?
I've got a buddy w a 99 F150 5.4 w 150K on it. He was having problem with it going dead when getting hot, even at highway speeds. He said that there was not really a pattern to it. It finally got to the point where it died and would not restart.
I went to look at it today and tried to connect to it to see if it had any stored or pending codes, but my scan tool would not connect to the computer in the truck at all. Tried several different times and it would not connect. This is a not a $100 scan tool, it's a professional technician's tool. Connected to other vehicles just fine.
The truck was acting a bit wonky on the dash, too. Odometer was not on at all. At times the "THEFT" light would blink for a few seconds and then go off. Tried another key to see if the main PATS key had gone bad, but no joy there either.
The trunk cranks and spins over fine and fast, but does not fire. With the failure to connect to the computer by the scan tool, I'm suspecting the PCM. There is a sticker on the air cleaner that shows that Ford replaced the original PCM in 2001.
Any thoughts?
I went to look at it today and tried to connect to it to see if it had any stored or pending codes, but my scan tool would not connect to the computer in the truck at all. Tried several different times and it would not connect. This is a not a $100 scan tool, it's a professional technician's tool. Connected to other vehicles just fine.
The truck was acting a bit wonky on the dash, too. Odometer was not on at all. At times the "THEFT" light would blink for a few seconds and then go off. Tried another key to see if the main PATS key had gone bad, but no joy there either.
The trunk cranks and spins over fine and fast, but does not fire. With the failure to connect to the computer by the scan tool, I'm suspecting the PCM. There is a sticker on the air cleaner that shows that Ford replaced the original PCM in 2001.
Any thoughts?
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
My thoughts from what you post are the PCM relay, or a fuse position may be intermittent.
The dash response may be a second issue or the result of the root cause.
If the PCM is out of power, the PATS system can't communicate with it so there is a problem there as a secondary result.
Turn the ignition to 'run' let set a few minutes and see if the Theft lamp flashes a two digit code, post it here as a start.
The dash diagnostics may be tried to see if it reveals a clue.
The DLC is supposed to have power on one pin to power your scanner.
If it's power source is missing you can't connect with any tool.
Bottom line is more checks have to be made before suspecting the PCM.
Look in the fuse/relay section of the owner manuel for these assignments and check them out first.
Looks very much like an intermittent power issue, overall.
Good luck.
The dash response may be a second issue or the result of the root cause.
If the PCM is out of power, the PATS system can't communicate with it so there is a problem there as a secondary result.
Turn the ignition to 'run' let set a few minutes and see if the Theft lamp flashes a two digit code, post it here as a start.
The dash diagnostics may be tried to see if it reveals a clue.
The DLC is supposed to have power on one pin to power your scanner.
If it's power source is missing you can't connect with any tool.
Bottom line is more checks have to be made before suspecting the PCM.
Look in the fuse/relay section of the owner manuel for these assignments and check them out first.
Looks very much like an intermittent power issue, overall.
Good luck.
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Junior User
Joined: May 2008
Posts: 69
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From: Friendswood, TX
Well, my plans were to go back over and replace the PCM relay(s). I had my check for theft codes, but he said that the THEFT light was not flashing. I know it was yesterday, but I didn't count the flashes. I know it was flashing a code because I did notice it flashed for a while and then went out. Before I got there, my buddy had it towed to a shop to work have it worked on. He's got more money than time or interest in messing with the truck.
The very sad part of the story is that when I called today, he was at the dealership looking at new Toyotas!! Nooooooooo!!!!
The very sad part of the story is that when I called today, he was at the dealership looking at new Toyotas!! Nooooooooo!!!!
Fleet Mechanic
Joined: Jul 2010
Posts: 1,354
Likes: 31
From: Winnipeg
As Bluegrass stated the scanner won't read without a power source. Most times the power is on the same circuit as the cig lighter. That fuse is usually shorted from defective accessory plugs used and malicious dimes put in the lighter receptacle. lol
Might work for you buying his used truck when he gets a new one.
Might work for you buying his used truck when he gets a new one.
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