Drive Mode
The system carries out a self-check after start-up. At the same time, the return pump in the hydraulic control unit (HCU) also starts up briefly (this may be felt in the brake pedal). If a fault is found in the process, the antilock warning indicator lamp illuminates. Any system faults which occur while driving also cause the antilock warning indicator lamp to illuminate and stay on constantly.
If the antilock warning indicator lamp comes on while driving and then goes out again after a short time, the cause may be battery under-voltage.