2006 F-350 The trailer fault indicator has started coming on. The truck has a western plow on it. When I put the test light on the trailer plug on the electric brake terminal, the fault light goes out. This problem occurs only when it snows or at the car wash. It says trailer fault when not hooked to a trailer. When a trailer is behind, this problem doesn't exist. Do you have any ideas?? Mike
It sounds like you are getting water intrusion in the trailer connector. Clean the connector out really good and pack the connector with dielectrical grease this should take care of the concern.
I pulled the connector apart and greased terminals and it still gives the code when I apply the brake or turn on the left signal. Is there another connection to check ?
If there is no water intrusion than you either have a wiring problem or module problem.
Do you have a volt/ohm meter?
Everything looked fine, I didn't see any moisture. Yes I do have a meter.
Here is the pinpoint test for the trailer fault. It is easier if you have the trailer brake module scanned for codes.
NOTE: Make sure the trailer brakes are electric-magnet actuated drum type brakes before proceeding with this pinpoint test.
NOTE: Every 4 seconds a voltage pulse is applied to circuit 43 (DB) to determine whether or not a trailer is connected to the 7-pin trailer tow connectors.
NOTE: Battery voltage must be greater than 10 volts.
Ford Senior Master tech, ASE certified