Audi A4FSI - Trailer taillights are permanently ON | HELLA
Audi
A4FSI
Model series 2002
Equipment series including trailer hitch
This may possibly be caused by the control unit for trailer detection, which converts the vehicle's lighting system comfort CAN messages from the electrical system control unit into trailer lighting.
Diagnostic procedure:
- Read out event memory of the control unit for the trailer function.
- Check the correct functioning of the comfort CAN bus and trailer control unit's voltage supply.
- (The control unit is installed in the boot's wheel arch, on the left side).
- If the signals measured with the oscilloscope are ok, the malfunction must be caused by the defective control unit for trailer detection.
Note:
In the case of incorrect communication between the trailer detection control unit and the control unit for on-board voltage, the taillights are actuated as an emergency function.