how would i know if the pcm is the problem.

Question

on the heater circuit there is a pink wire that's 12v. fused and a black w/ white stripe that's a controlled ground from pcm. I have 12v to pink down thru oxygen sensor back up thru black/white stripe wire all the way to c2 pin 37 at the pcm. I was told that the pcm will ground this black wire and I can't seem to tell if it is. I can't seem to get a ground from the pcm. not sure if it the pcm . 2003 buick century 3.1L engine.