Towing / Trailer System: Testing and Inspection

Trailer Module: Currently Known Fault Patterns

Trailer module: Currently known fault patterns
The functional description describes currently known fault patterns of the trailer module and trailer interlock for the following vehicles:
- E81, E87, E90, E91, E92, E93 (BMW 1-Series, 3-Series)
- E60, E61, E63, E64 (BMW 5 Series, 6 Series)
- E65, E66, E67, E68 (BMW 7 Series)
- E70 (BMW X5)
- R55, R56 (MINI)

These fault patterns can occur on all vehicles and are sorted below into fault patterns of the electrical swing-out and electrical release trailer coupling of the trailer module in general (lighting). These fault patterns are not registered by the self-diagnosis of the control unit. The fault patterns are symptom-based and intended as supplementary information for the present diagnosis.

Currently known fault patterns of the trailer module AHM3
- The lighting on the trailer does not work although all the trailer lights and the wiring have no faults.

- Description
The customer complains that the trailer lighting is not functioning. Check Control messages for the lighting also appear. No fault codes are stored in the fault memory.

- Cause
The trailer of the customer is equipped with a lighting system that has a higher power requirement. The trailer module detects this excess current at the outputs for the lighting. This means that the trailer module disables the corresponding outputs.
Two variants of this problem currently occur.
- Trailers that are equipped with an additional stop light and no other changes / extensions have been made to the lighting system.
This affects vehicles with production date before 03/2006. These trailer modules must be programmed with the current DVD. The problem is then rectified.
- All other trailers with extended lighting (e.g.: additional limit lights, auxiliary turn indicator lights, raised lighting, etc.)
To use these trailers, the trailer module must be replaced by a more powerful AHM3+. This trailer module is specially designed for trailers that have a higher electrical power requirement. To this end, a second supply lead is to be routed to the trailer module. The newly installed trailer module is to be coded. This affects vehicles with production date before 09/2006.

Procedure
- Remove the trailer module.
- Fit a new AHM3+ (see repair instructions RA 6135001 "Removing and fitting the trailer module").
- Route a second supply lead to the trailer module. Part number 61 129 130 258 (E90, E91, E92, E93, E87); 61 129 128 792 (E60, E61)
- The supply lead is to be pinned into chamber 2 of X609.B on the trailer module side.
- Subsequently, the supply lead must be routed to the front distribution box on the wiring harness and pinned in as follows. E90, E91, E92, E93: X11006 chamber 3E60, E61: X11004 chamber 3E65, E66: X4884 chamber 5
- Fit a 30 Ampere fuse to the supply lead. Then the newly installed trailer module is to be coded.

Known fault patterns for the electrical swing-out trailer coupling
- The towbar is inoperative, a Check Control fault message (towbar not locked) occasionally appears while driving. Affected vehicles: E90 and E91.

- Description
The customer complains that the electrically extendable towing hitch is inoperative.

- Cause
Water ingress in the control unit for the electrically extendable towing hitch, caused by obstructions in the panorama glass roof water drain hose, leak in the fuel filler cap lock, Touring side window, for example.

- Electrical swing-out trailer coupling without function

- Description
The customer complains that the trailer coupling release is not functioning. The trailer coupling cannot be released electrically and does not swing out. The fault memory contains no fault for the trailer coupling release. However, other faults can be stored. The indicator light in the button for the trailer coupling release flashes slowly red (2 Hz).











- Cause
A possible cause for this fault pattern can be that water has entered through a faulty (squashed) sealing ring into the drive mechanism of the trailer coupling. Water can also enter the drive mechanism at the cable entry point
Another cause can be a failure of the micro-switch. This micro-switch detects the end position of the ball end. If this micro-switch is defective, the trailer module does not detect the position of the ball end. The ball end can then only be swung out with emergency activation. A short circuit caused by water entry can be the cause of this fault.







Known fault patterns for the electrical release trailer coupling
- The electrically released trailer coupling swings directly into the pivoted-out limit position when released
- Description
The customer determines that the trailer coupling is released by pressing the unlock button and then locks in place directly in the articulated outwards end position. The specified released intermediate setting is swung over.

- Cause
The cause of this behaviour is related to the manufacture. On swinging out, the ball end is braked by a rubber mat with a defined torque. The manufacturing tolerance mean that this braking torque can be too low. This enables the complete swing-out to the end position. At the moment, there is no remedial measure, as the braking torque is set at the manufacturer and cannot be changed in Service (permanent bonding).

We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.