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On a 2004 Super Duty, diesel or gasoline engines, the PCM power relay diode is internal to the instrument panel fuse box and is "non-serviceable." If you haven't already you can check it by measuring continuity to ground at terminal 85 of the PCM power relay.
 

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Discussion Starter #3
Yes I have checked continuity from terminal 85 to the PCM and it was good. it Was cranking with no start so I replaced batteries as they were due for replacement. Put them in the truck and it would crank with no start and then it didn’t crank at all. Tested starter and it worked. Any other suggestions? Thanks
 

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Yes I have checked continuity from terminal 85 to the PCM and it was good.
Pin 85 at the fuel pump relay goes directly to chassis ground, not the PCM.

Was cranking with no start so I replaced batteries as they were due for replacement. Put them in the truck and it would crank with no start and then it didn’t crank at all. Tested starter and it worked. Any other suggestions? Thanks
FYI the PCM controls the starter therefore if the truck WAS cranking the PCM/relay is not your problem.

It would seem you now have two issues. You HAD a crank/no start condition. Now you have created a no crank condition. I recommend retracing your original steps - check the battery connections and verify your fuses, consult your owners guide for all fuses related to the PCM and the run start relay.
 

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Well I changed the PCM I got from the wrecker and truck turned over. I guess I need to go to the dealer to program the truck?
 

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If it cranks it's working but if the donor truck was similar to yours and the same year it should work. Ultimately you will want/need to have the PCM programmed at the dealer with "AS Built Data" which will restore the factory programming based on the VIN. Back to your crank/no start diagnosis. Are you using a scan tool?
 

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In any case, you will need to program it, even if you take it from a donor. When I have some problem, I car vin number check, and then look for the necessary parts. They may come from different models in fact. Ford_Doctor case says
 
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