Mostly putting this out as info and for Steve, let'* all learn as we go.

Got a buddy with a 97 GTP. Pulled the car in and did a trans swap along with engine pull for gaskets etc. Everything went w/o a hitch on the install. Only issue that'* coming up is a P0748 code. This is electrical PCS/EPC soleniod.

Diagnostics/items done:
Pulled the trans connector and checked the soleniod for the proper ohms. At 190F it should have 5-6K ohms. It had 8k ohms. We pulled the side cover and replaced with new soleniod.
Still have code
Checked wiring from pcm to trans connector. Power wire was shorted to ground from pcm connector, no connection to trans connector. Ground wire was not making contact between pcm and trans connectors. Reran both wires with new and retested as good.
Still have code
Tested every fuse in vehicle as good. The power is a pulse width modulated and I'm not sure if it'll show on a DMM
Still have issue
Reflashed the pcm
Still have code
Changed the pcm
Still have code

My thoughts at this point are that two wires in a loom don't go bad w/o potential to others having an issue. Yet I can't find the power source for the pcm to send to the EPC soleniod. I'd like to know where power is coming from to retest it directly. Next up is pulling loom and finding the break in the ground and the short in the power wire to the trans connector. It should be that area where any other issue would be possible.

Anyone got other ideas?

The EPC power wire should come rirth off the PCM.
An electrically generated code can only be caused by 3 things:

1-Solenoid
2-Wiring
3-Computer

I can't find a diagram here on line, but I have Alldata @ work.

I'll assume this is why I saw missed call from billboost on my phone today.

Do you have a spare wiring harness to try? You changed the solenoid, so unless you have another DOA that should be good. I don't see the computer being a problem because you reflashed it. That leaves the harness. You already found a bad wire, so I would replace it.

That'* the thing guys.

Replaced the soleniod with a good one

Found an issue on the power to soleniod wire and a break in the ground to
soleniod. Replaced both wires from pcm to trans.

PCM was reflashed and replaced

The only thing I can think of at this point is the input power for the pcm to send to the soleniod. But can't locate where that power is supplied from and all fuses appear to check out as good.

Darn GM DVD is in the mail to me, but it'* not here yet. Anyone got the pin or fuse for the power coming in that supplies the pcs? I figure the short to ground or wiring issues caused further problems upstream.

Hope I'm understanding you on this. But, one wire from the EPC is purple/pin C, that changes at the plug to red/black and goes to the PCM. The other wire is lite blue/pin D, changes at the plug to blue/white and goes to the PCM.