Removed frt pass side window regulator to check for normal operation works fine/up and down. Checked window motor with pwr probe for normal operation works fine/ up and down. Checked window switch with a known good switch/up not down. Checked wire harness driver side door no broken wires. Also checked drivers side rear pwr window all steps above same results/ up not down. S
The body control module may regulate current flow. On older systems it was just a straight wire, no computer function. If the BCM is malfunctioning this would explain your issue. A bad ground can cause this as well. If it's a complicated circuit, sometimes you have a ground for up and ground for down. Sounds more like a BCM issue though. You need to trace from the switch directly ALL of the way through the circuit and see whats not getting juice. "www.eautorepair.com" has a plethora of wiring diagrams. Especially for GM vehicles. Since other windows are effected as well, I want to say BCM or ground. Just ran into this problem not too long ago with a dodge charger. The dealership couldn't figure it out, and it took us almost 10 hours to figure out it was the BCM "sigh". Hope this helps a little.