I know this is over a year old, but jimjokjv did you ever get this figured out? I have an '01 Excursion (Cali model w/ GPCM) and have been having some glow plug issues, so I would love to know if you got this figured out, and if so, what the solution was. Thanks!

 

What I found is that my glow plugs are working just fine but my PCM still throws a code.
I pulled the inner fender and checked continuity on all the wiring from the PCM plug through the 42 pin connector to the GPCM. Everything checked out. My truck will start in 15 degree temps with one cycle of the glow plugs.
As to the PCM throwing the code, my only option is to send it in and have it tested. I plan to do that someday but right now I need the truck and can't do without it for a week. Replacement PCMs for the CA version trucks are upwards of a $1000 for what I have found and not in my budget.

 

Thanks for the quick answer! I recently had my PCM gone through, ran me about $600 IIRC. What was worse was they had it for almost a month and wouldn't return my calls requesting status updates, then it finally just showed up at my doorstep. I had been told they would turn it around in a week + shipping so I didnt feel bad bugging them after 2 weeks.

 

I sent pics of my PCM to Diesel Technology and he stated that my PCM is unusual and circled some components that are different or not normally there. I plan to send it in when I know I won't be needing the truck for a week or so (probably when the weather is nice enough to ride my Harley ).
One thing to check is that your connector plugs are properly seated in the GPCM. I had one that the seal had rolled slightly and wasn't seated all the way. I got them together and then put Zip Ties to hold them in place.
The wiring for the top of the engine has a few places where chaffing can occur and on these older trucks it is not uncommon to find wires with the insulation scraped off to run continuity checks.
I pulled the top harness from the 42 pin connector and then removed all the wires from the wire loom to look at them. I then tested each circuit with an ohm meter while wiggling the harness to see if there were any breaks in the wires there were not visible. Didn't find any problems but it did give me peace of mind.