GF42.20-P-0001SX Electric Parking Brake, Function

GF42.20-P-0001SX Electric parking brake, function

Component Identification:

Function
The electric parking brake (EFB) operates the parking brake at the rear axle via cables by an electric motor integrated in the controller unit.

Activation takes place manually via the electric parking brake switch or automatically depending on the driving condition.

The electronic parking brake is operational as soon as the power supply terminal 30 is present.

A manual unlocking makes it possible to release the EFB also in the event of a defect and in the de-energized condition. The release cable is located in the fuel filler flap and can be operated with the help of the vehicle tool kit.

The electronic parking brake contains the following functions:
^ Apply and release the parking brake
^ Automatic parking brake release
^ Emergency braking
^ Test bench mode

Apply and release the parking brake

Function requirement
^ Speed less than 3.5 km/h or vehicle stationary
^ Terminal 15R On or with code (889) Keyless Go terminal 15 On (only for releasing the parking brake)

Function
When the electric parking brake switch is operated a signal is transmitted directly to the controller unit. Depending on the condition the controller unit releases or tensions the brake cables via the integrated electric motor.

The operating period of the electric parking brake switch does not have any influence on the function.

Automatic parking brake release

Function requirement
^ Engine runs (terminal 61)
^ Selector lever position "D" or "R"
^ Engine hood closed
^ Trunk lid closed (only in selector lever position "R")
^ Driver door closed (only if driver is not wearing the seat belt)

Function
The function is triggered when the accelerator pedal position exceeds a certain threshold. The controller unit is awoken via the corresponding CAN-messages and releases the brake cables via the integrated electric motor.

For the case that the electronic parking brake does not release the display "Release parking brake" is displayed in the instrument cluster and a warning tone sounds.

If terminal 30 has been interrupted, automatic release is not possible. The electronic parking brake must first be woken via the Electric parking brake switch or terminal 87. The controller unit receives the signal terminal 87 directly from the front SAM control unit with fuse and relay module (N10/1).

Emergency case braking with the electric parking brake switch

Function requirement
^ Speed greater than 3.5 km/h

Function
When the Electric parking brake switch is operated and held, the braking request is transmitted to the ESP control unit. The vehicle is now braked via the service brake, ABS or ESP interventions are also performed if necessary

The stop lamp actuation is activated.

The display "Release parking brake" appears in the instrument cluster and a warning tone sounds.

In the event of a service brake malfunction (e.g. CAN communication faulty) the brake application takes place by the controller via the parking brake.

Similar to an ABS a control intervention takes place when blocking of a rear wheel is detected by the rpm sensor.

Test stand mode

Function requirement
^ Front wheels "stationary" and rear wheels turn slowly (roller brake test stand)
^ ESP Off switch (S6/2s11) operated

Function
The controller unit is actuated by operating the electric parking brake switch. The force is built up at the brake cables in a constantly rising manner until the maximum force is applied. As a result for example the linings of the parking brake can be bedded in or the deceleration values determined.

The process can be repeated up to 3-times, in which a cooling off time should be maintained between the brake applications.

Brake cable replacement
To replace the brake cables the electronic parking brake is either brought into the assembly position or unlocked manually. Once the work is complete the electronic parking brake is again put into the operational condition by pressing the electric parking brake switch.