Audi A4   Controls   Driving  Electro-mechanical parking brake
This feature enables you to stop the vehicle if the main brake system should fail or if the pedal is obstructed.
To stop the vehicle with the parking brake in an emergency, pull and hold the parking brake switch -A- Fig. 1.
The brakes will be released immediately if you release the switch -A- or press down the accelerator.
If you pull and hold the parking brake switch -A- at a road speed above about 8 km/h, this will initiate an emergency brake application. The brakes are then applied hydraulically at all four wheels. The effect is the same as an emergency stop (full brake application) WARNING!
To prevent the emergency braking function from being used accidentally, a warning buzzer sounds when the switch -A- is pulled. The brakes are released immediately when you release the switch -A- or press down the accelerator.
WARNING!
You should only use the emergency braking function in a real emergency, for example if the brake system were to fail or if the brake pedal were to be obstructed. If you use the emergency braking function by activating the parking brake switch, the effect is similar to a full brake application (emergency stop). Please remember that the ESC (with its combined ABS, EDL and traction control functions) is still subject to certain physical limits. In a corner or in bad road or weather conditions an emergency stop can cause the vehicle to skid or lose steering control.

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