I have seen posts on this forum by people facing the issue where the remote unit won't pair and keeps displaying "NC" on display. I recently encountered the same problem with my brake controller and was able to find a solution, so sharing here.
I have a Tekonsha 90250 Prodigy RF Electronic Brake Control. When we bought our AS in 2018, the dealer paired it with our then tow vehicle, GL450. It worked all these years perfectly until a few months ago when I used this TV to pull the AS from storage to home. The display kept on showing "NC." I couldn't figure out a solution then. I didn't care as much as our primary TV; RR HSE could pair it properly. But a few weeks ago, the same thing happened with RR while bringing the AS back from storage; now, it won't pair with the RR. I had to borrow my neighbor's truck to pair it for the trip.
Doing some thinking about the pattern of failures while towing from the storage made me think that it could be a blown fuse in the TV because both times, the AS batteries were down from being in the storage for a while, so the trailer jack might have put too much load on the TV socket whiling hitching the AS. When I checked the fuse box, I found out that the hitch fuse was blown. Replacing the fuse fixed the issue. After coming back from the trip, I checked the GL450 and found the same problem. Both TVs now pair correctly. Hopefully, this will help someone.
I found
this kit to be very helpful for this troubleshooting exercise as well as general maintenance of the trailer socket.