Cranks wont start
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Joined: May 2007
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Cranks wont start
I have a 2001 F150 XL, 2WD, 4.2L, Auto at work. It will intermittently crank but not start, also, my scan tool will sometimes not connect to the truck. The only code I ever get is 1 about not being able to connect to self diagnostics. I have narrowed it down to the PCM relay in the underhood power distribution module not turning on because it SOMETIMES only sees a 2 volt turn on signal instead of 12 volts. I have replaced the ignition switch on the steering column- initially I thought that took care of it. But as I was about to put the meter away it did it again. If I remove and reinstall the diode that is in the PDM, sometimes more than once, I can get it to turn on. Are these diodes available from any one besides Ford? Any other ideas to fix this? the wiring diagram in my Haynes manual is very generic and does not show the circuit from the ignition switch to the fuse box. Where can I find a GOOD and complete wiring diagram for free on the net so I can print it out and take it with me to work?
Hotshot
Joined: Jan 2004
Posts: 19,762
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From: St Louis
Here's a copy of the relevant circuit: https://drive.google.com/file/d/0B3e...ew?usp=sharing
In a pinch, you can use a 1N4004 diode (Radio Shack 276-1103) as a substitute for the factory part. You will need to carefully observe the orientation of the diode so that the banded end is installed the same direction as the original keyed diode. I've not come across any aftermarket replacements but you can likely scavenge one from another vehicle if you believe you really need to.
Those diodes don't fail very often (I've never seen one go bad), so be on the lookout for something else like a poor connection in one of the fuse boxes or a fault in the wiring that causes a poor connection. Since that diode is fed from the ignition switch via F30 under the dash, look for any evidence of corrosion on the fuse and the harness connectors due to water infiltration. Tighten the prongs that hold the diode and the fuse in case they're loose.
In a pinch, you can use a 1N4004 diode (Radio Shack 276-1103) as a substitute for the factory part. You will need to carefully observe the orientation of the diode so that the banded end is installed the same direction as the original keyed diode. I've not come across any aftermarket replacements but you can likely scavenge one from another vehicle if you believe you really need to.
Those diodes don't fail very often (I've never seen one go bad), so be on the lookout for something else like a poor connection in one of the fuse boxes or a fault in the wiring that causes a poor connection. Since that diode is fed from the ignition switch via F30 under the dash, look for any evidence of corrosion on the fuse and the harness connectors due to water infiltration. Tighten the prongs that hold the diode and the fuse in case they're loose.
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