Fault code 0526: Diagnosis/troubleshooting

NOTE: The trailer hitch control module receives the brake light signal in two ways: as an analog signal via the signal wire (plug B, pin 3) and also via the CAN comfort bus from the PSM. A cyclical check and comparison of both sets of information takes place in the trailer hitch control module (redundancy). If different comparison values are detected, a fault is stored in the fault memory.

DIAGNOSIS/TROUBLESHOOTING PROCEDURE

Work instruction			Display OK	If not OK
1	Check fault memory in the trailer hitch control module for further faults		Further faults present. => Correct the faults.	Go to Step 2
2	Check fuse F38 and F26 (fuse carrier at left of dashboard)	Check fuse for continuity.	< 5 Ω Go to Step 3	Replace fuse. → End
3	Check whether brake signal is present on plug B, pin 3, of the trailer hitch control module	Switch on ignition. Actuate brake pedal. Measure voltage between plug B, pin 3, on the trailer hitch control module and ground.	Brake not actuated: < 0.3 V Brake actuated: 11.4 - 14.5 V Go to Step 6	Go to Step 4
4	Check brake light disabling relay (Caution: special relay with additional resistor)	Check relay for continuity and correct gearshift in accordance with the circuit diagram	Go to Step 5	Replace relay. → End
5	Check signal lead from brake light switch	Check signal lead and supply leads from the brake light switch to the trailer hitch control module for open circuits and short circuits.	Go to Step 6	Repair or replace brake light switch or signal lead. → End
6	Continue troubleshooting, refer to CHECKING INSTRUCTIONS/CAN DATA BUS .		→ End