Hi,
I haven´t got a manual yet but I think there are three alternatives:
1. Brake fluid on low level
2. Brake accumulator (pressure reservoir) is worn out.
3. Hydraulic oil level is low

1. Check fluid level. If it is low, find out the reason why. Worn brake pads, or some leakage (hoses, pipes, master cylinder) might be the cause.

2. If the dashboard indicates the sign after engaging the brake pedal for a couple of times, the accumulator is definitely worn. In this case, there is even no more brake boost available. The bake pedal feels as hard as stone under this conditions.

3. Check oil level. If it is low, check for leaks.


Beste Grüße
Tim