Troubleshooting a NC Error Message on a Prodigy P2 Brake Controller

Updated 05/27/2025 | Published 05/14/2025

Question:

I have a 2020 Merecedes Sprinter 3500HD. Just installed a Prodigy P2 brake controller. Everything seems fine except the gain numbers do not show up. It keeps say NC for not connected although the trailer is connected to the vehicle. All the lights work on the trailer and the manual braking works when I move the switch on the controller. The problem is, since the numbers for gain dont come in and it says NC, I have no idea if the brakes are working or not when driving. Also I cannot adjust the gain so no idea if they are helping or not. It doesnt help that the vehicle is 12,000 pounds so it is hard to really tell if the trailer brakes are working or not. I have checked everything. From the trailer connecting, I get 14.4 volts when I use the manual braking switch on the controller it is either zero or 14.4 volts, nothing in between. So, it is getting power but I get nothing stepping on the brakes. I am wondering if this has something to do with the connection between the brake pedal and the controller? Any help would be appreciated.

asked by: Chuck

Expert Reply:

Hey Chuck! It sounds like you hooked up the Prodigy P2 item # 90885 to the wrong wire by the brake pedal when you installed it. That's why you're getting an all or nothing voltage reading.

You need the cold side of the stop light switch on your Sprinter. You'll want to use a circuit tester like item # PTW2993 to find it. The wire will be near the brake pedal, and will be the one that only has 12V power when you press on the brakes.

There are only 4 possible causes for NC to display on the Prodigy P2 item # 90885. You've already crossed 1, 3, and 4 off. The manual override wouldn't work if the connector was corroded.

1. Trailer not connected to tow vehicle.
2. Trailer connected with open circuit on brake line.
3. Trailer connector disconnected or corroded.
4. Loss of trailer brake magnet ground.

expert reply by: Jerred H

Chuck

5/23/2025

Thank you and it was the issue. The rv dealer that installed the brake controller reversed 2 wires. Instead of buying the correct connection, they cut the plug off the sprinter and used spare wire to make the connect. I spent 3 hours taking everything out plus the drivers seat and found the wires reversed. Once I corrected the issue, everything worked correctly! I should have installed this myself instead of saving a few buck and Jerry rigging the connection. Thanks. Note, the wires in the sprinter are brown/yellow, red, thick blue and thin blue. If the connector is not there, you can google what each wire is. The two wires backward was the 2 blue wires. One is thick and the other is thin. Very easy to tell. Just swap the connections and you will be good to go.

Jerred H.

5/23/2025

@Chuck Glad you got that sorted out and up and running. Thanks for the heads up on the wire colors. Did you go back to the installer and say something?

Chuck

5/24/2025

@JerredH no I have not gone back to them. I doubt anything would come about it.

Jerred H.

5/27/2025

@Chuck Good to know. Was curious what their response would be. Those plug in connectors do cost a bit more than splicing it in. What you're really paying for is removing the human error part. Let me know if you have any additional questions or concerns down the road.