Troubleshooting Bad Ground on Trailer Brake Circuit

Published 12/21/2017

Question:

What can we do to fix and will our braking system still work

asked by: Diane H

Expert Reply:

With the Prodigy P2 trailer brake controller # 90885 the troubleshooting code 9 indicates that the controller detects the connected trailer but is losing its ground connection to the host vehicle. This ground connection is essential for the unit to deliver braking power to the trailer through the 7-way connection.

All brake controllers use the same 4-wire color-coded connections. Red wire for brake light signal; blue wire for output; black wire for 12V operating power; and the WHITE wire is ground. This wire needs to connect to the battery ground. The ground connection can be made through a vehicle's under-dash brake controller connection port (for popular tow-capable vehicles like a pickup truck that have this feature) or it can be a hardwired connection direct to the battery ground terminal if the controller was installed by hardwiring it. Either way, that white ground wire must be solidly connected to the battery ground. So what you want to do is try to find the connection point in the wiring where the ground is being lost.

If your vehicle uses an under-dash connector for the controller you can unplug this from both the under-dash port and from the back of the controller to check the two contacts for the white wire. A corroded or bent contact could be the issue.

Also check the 7-way socket on the back of the vehicle for the same potential corrosion issue and for a bent pin. Check the main ground wire on the trailer where it connects to the frame and the ground contact on its 7-way plug.

expert reply by: Adam R