Precheck is always closed. I have flown through C gates 25-30 times in the last year and haven't been able to use precheck once. One time I complained and they said precheck at D gate was open so I walked down there. D gate wasn't any better, Precheck was closed and it had a longer line than C gate did.
On a positive note, the pat downs are slightly more invasive at C gate than D gate.