See also:

Problems with PARKTRONIC
...

Range of the sensors
General notes The sensors must be free of dirt, ice and slush; otherwise they may not function correctly. Clean the sensors regularly, taking care not to scratch or damage them. Side view ...

ETS/4ETS (Electronic Traction System)
WARNING Observe "Important safety notes". Traction control is part of ESP®. Traction control brakes the drive wheels individually if they spin. This enables you to pull away and acc ...