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

Model 205, 253 

Courtesy of MERCEDES-BENZ USA

Up to model year 2019 except engine 177, as of model year 2019 

Courtesy of MERCEDES-BENZ USA

Up to model year 2019 with engine 177 

Function requirements, general 

• No undervoltage or overvoltage

Electric parking brake (EFB) in general 

The electric parking brake (EFB) holds the vehicle at a standstill on uphill and downhill gradients, whereby the braking components are held in the de-energized braking position by a self-locking mechanical effect. The Electronic Stability Program control unit or the electric parking brake control unit actuates the electric parking brake actuator motors directly for this purpose.

The electric parking brake (EFB) can be manually activated using the electric parking brake switch or automatically. The clamping force of the electric parking brake actuator motors is increased or reduced to match the requirement. The system status is indicated by the parking brake indicator lamp (red), the parking brake warning lamp (yellow) and through text messages in the instrument cluster.

The electric parking brake (EFB) can also be activated through external requests (e.g. from the standstill control).

Childproof loocks 

The child safety lock prevents any unintentional releasing of the electric parking brake (EFB).

The request to release the electric parking brake through the electric parking brake switch is ignored when circuit 15 (Ignition ON) is not activated.

The electronic ignition lock control unit sends the status of circuit 15 to the Electronic Stability Program control unit or the electric parking brake control unit.

Dynamometer test mode 

To enable the electric parking brake (EFB) can be tested on the brake test stand, the dynamometer test mode must be activated.

The Electronic Stability Program control unit or the electric parking brake control unit detects the brake test through evaluation of the wheel speeds. The roller test mode is activated when a difference is detected between the rotational speeds on the front and rear wheels. The inspector can operate the electric parking brake switch several times to gradually increase the clamping force of the electric parking brake (EFB).

The electric parking brake (EFB) includes the following subfunctions:

• Operate electric parking brake (EFB) 
• Automatically release electric parking brake (EFB) 
• Automatically engage electric parking brake (EFB) 
• Emergency braking 
• Issuing of control and warning messages 

Operate electric parking brake (EFB) 

The electric parking brake (EFB) can be manually operated using the electric parking brake (EFB) switch. Press electric parking brake (EFB) switch: The EFB is applied. Pull electric parking brake (EFB) switch: The EFB is completely released.

The Electronic Stability Program control unit or the electric parking brake control unit directly read in the status of the electric parking brake switch. The Electronic Stability Program control unit or the electric parking brake control unit actuates the electric parking brake actuator motors. The Electronic Stability Program control unit or the electric parking brake control unit sends the request to switch the parking brake indicator lamp (red) on or off to the instrument cluster. The parking brake indicator lamp (red) on the instrument cluster then lights up or goes off.

To avoid any incorrect operations, temporary, or any unwanted operations are ignored.

Additional function requirements for automatically releasing electric parking brake (EFB) 

• Engine running
• Driver seat belt fitted or driver front door closed (driver presence check)

The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal to the Electronic Stability Program control unit or the electric parking brake control unit.

The Supplemental Restraint System control system sends the status of the driver seat belt to the Electronic Stability Program control unit or the electric parking brake control unit.

The left front door control unit sends the status of the driver front door to the Electronic Stability Program control unit or the electric parking brake control unit.

Automatically release electric parking brake (EFB) 

As soon as a sufficiently high drive torque is applied to the wheels on the rear axle to enable the vehicle to drive off, the electric parking brake (EFB) is completely released.

The following conditions must be fulfilled here:

• Driver seat belt fitted:
  • Transmission 716: 
    • Forward or reverse gear engaged and accelerator pedal operated
  • Transmission 722, 724, 725: 
    • Transmission in position D or R and accelerator pedal operated
    • Shitf from transmission position P to position D or R (on large inclines with accelerator pedal also pressed)
  • Driver seat belt not fitted and driver front door closed:
    • Transmission 716: 
      • Vehicle speed before switching off the vehicle over 3 km/h
    • Transmission 722, 724, 725: 
      • Gear shift out of transmission position P
      • Vehicle speed before switching off the vehicle over 3 km/h

    The trunk lid or the liftgate must be closed when reversing.

    The Electronic Stability Program control unit or the electric parking brake control unit evaluates the initial situation by evaluating the following variable:

  • Forward or reverse gear engaged (transmission 716) The powertrain control unit sends information on the engaged gear to the Electronic Stability Program control unit or the electric parking brake control unit.
  • Selector lever position (transmission 722, 724, 725) 

    The steering column tube module control unit sends the current selector lever position to the Electronic Stability Program control unit or the electric parking brake control unit.

  • Drive range (transmission position) (transmission 722, 724, 725) The fully integrated transmission control unit sends information on the engaged drive range to the Electronic Stability Program control unit or the electric parking brake control unit.
  • Accelerator pedal position 

    The powertrain control unit sends information on the accelerator pedal position to the Electronic Stability Program control unit or the electric parking brake control unit.

  • Trunk lid/liftgate status 

    The rear SAM control unit sends the status of the trunk lid or liftgate to the Electronic Stability Program control unit or the electric parking brake control unit.

  • Yaw rate, lateral and longitudinal acceleration, road inclination (at vehicle standstill) 

    Information on the yaw rate, lateral and longitudinal acceleration as well as the road inclination is recorded by the acceleration sensor in the Supplemental Restraint System control unit. The Supplemental Restraint System control unit sends this information to the Electronic Stability Program control unit or the electric parking brake control unit.

  • Engine torque 

    The CDI control unit or the ME-SFI [ME] control unit sends information on engine torque to the Electronic Stability Program control unit or the electric parking brake control unit.

    On uphill gradients over 5 % the engine torque is also evaluated.

    The electric parking brake (EFB) is only released at a sufficiently high level of engine torque.

  • Vehicle speed 

The Electronic Stability Program control unit or the electric parking brake control unit calculates the vehicle speed from the wheel speeds.

The Electronic Stability Program control unit or the electric parking brake control unit releases the electric parking brake (EFB) through actuation of the electric parking brake actuator motors on the rear brake calipers.

If a fault prevents the electric parking brake from being released, the instrument cluster issues a "Release parking brake" message. The instrument cluster also actuates the instrument cluster speaker to emit a warning tone.

Automatically engage electric parking brake (EFB) 

If the vehicle is brought to a standstill, the engine switched off and the driver wishes to exit the vehicle, the electric parking brake is automatically activated.

The Electronic Stability Program control unit or the electric parking brake control unit evaluates the following variables for this purpose:

• Engine running status 

  The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal to the Electronic Stability Program control unit or the electric parking brake control unit.

• Status of driver seat belt 

  The Supplemental Restraint System control system sends the status of the driver seat belt to the Electronic Stability Program control unit or the electric parking brake control unit.

• Status of driver front door 

  The left front door control unit sends the status of the driver front door to the Electronic Stability Program control unit or the electric parking brake control unit.

• Request to active electric parking brake (EFB) through driver assistance systems 
  • Request through HOLD function:

    The HOLD function is activated by quickly pressing down hard on the actuated brake pedal after coming to a standstill. The Electronic Stability Program control unit or the electric parking brake control unit activates the electric parking brake.

  • Request through Distance Pilot (with code 239 (DISTRONIC Distance Pilot) or code 23P (Driving Assistance Package)): The "Activate electric parking brake" request is sent from one of the following control units to the Electronic Stability Program control unit or the electric parking brake control unit:
    • Radar sensors control unit (model 205 up to model year 2019 with code 23P (Driving Assistance Package), model 253 with code 23P (Driving Assistance Package))
    • Mercedes-Benz Intelligent Drive control unit (model 205 as of model year 2019 with code 23P (Driving Assistance Package))
    • Distance Pilot DISTRONIC controller unit (model 205 as of model year 2019 with code 239 (Distance Pilot DISTRONIC), model 253.99 with code 239 (Distance Pilot DISTRONIC))
    • Request through Parking Assist (model 205 up to model year 2019 with code 235 (Parking Pilot with PARKTRONIC), model 205 as of model year 2019 with code P44 (Parking Package) or code P47 (Parking Pilot with 360° camera), model 253 (except 253.99) with code 235 (Parking Pilot with PARKTRONIC), model 253.99 with code P47 (Parking Pilot with 360° camera)):

      The parking system control unit sends the "Activate electric parking brake" request to the Electronic Stability Program control unit or the electric parking brake control unit.

The Electronic Stability Program control unit or the electric parking brake control unit also activates the electric parking brake if a system fault occurs or the power supply breaks down.

If the electric parking brake is activated, the parking brake indicator lamp (red) lights up in the instrument cluster.

The Electronic Stability Program control unit or the electric parking brake control unit sends the status of the electric parking brake to the instrument cluster.

If the engine is switched off by the ECO start/stop function, the electric parking brake (EFB) is not automatically activated.

The powertrain control unit sends the "Drivetrain operational" signal to the Electronic Stability Program control unit or the electric parking brake control unit.

Operating the electric parking brake (EFB) switch can prevent the electric parking brake (EFB) from being activated.

Emergency braking 

If the electric parking brake switch is pressed and held while driving, the Electronic Stability Program control unit or the electric parking brake control unit interprets this as a brake request. The vehicle is then braked using the service brake. At the same time the Electronic Stability Program control unit sends the status of the service brake to the rear SAM control unit. The rear SAM control unit then activates the brake light actuation.

The Electronic Stability Program control unit or the electric parking brake control unit then sends the request to issue a message to the instrument cluster. The instrument cluster issues the "Release parking brake" message and actuates the instrument cluster speaker to emit a warning tone.