Trailer Hitch Control Module: Description and Operation

Trailer Module (AHM)

Trailer Module (AHM)
The trailer module is a peripheral module of the light module and only operates in conjunction with this module. It is fitted together with the trailer towing hitch special option.

It is necessary for disconnecting the load power circuit of the trailer from the current circuits of the towing vehicle thus enabling separate monitoring of the vehicle lamps and trailer power circuits.

Diagnosis takes place via the light module.

Turn signal indicator, side light, brake light
The trailer module receives the switch-on data for the turn signal indicator, side lights and brake lights via the lines connected to the rear lamps of the towing vehicle.

Rear fog light, reversing light, communication
The rear fog light and reversing light are not switched directly by the lamps of the towing vehicle as the corresponding lamps on the car must be extinguished with the trailer hitched up.

The trailer module communicates with the light module via a data link between the light module and trailer module.

The rear fog light and reversing light are controlled via this data link.

The trailer module transfers error messages to the light module with regard to faults in the trailer power circuits.

The rear fog light is switched off in the event of an interruption in communication between the light module and trailer module for more than two seconds.

Communication is re-attempted every time terminal 15 is switched on.

If communication between the light module and trailer module was already set up once and is now interrupted, the corresponding fault code is entered in the fault code memory of the light module.