If the problem described above is determined in conjunction with an activated cruise control system (Tempomat), the cause could be a faulty trailer control module.
Notes:
The problem is only evident when driving with Tempomat during automatic braking triggered by the adaptive cruise control system. If brakes are applied manually (brake pedal) to the vehicle which is towing and to that which is being towed, the malfunction does not occur.
Because of a software error in the trailer control module, the trailer stop lights cannot be controlled in the relevant, above-mentioned situation.
Remedy:
Replace the trailer control module with an improved version as per manufacturer's specifications. In such a case, contact an authorized specialist workshop.
The vehicle manufacturer has already addressed the issue and notified the owners of all the models concerned. For various reasons, however, it must be assumed that not all vehicles have been checked or rectified.
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