Electric Parking Brake, Function - GF42.20-P-0001GWM
Model 463 (except 463.342) as of model year 2019
Function requirements - electric parking brake (EFB), general
- No undervoltage or overvoltage
Electronic parking brake (EFB), 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 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 displayed via the parking brake control message (red), the parking brake warning message (yellow) as well as via text messages on the instrument cluster.
The electric parking brake (EFB) can also be activated through external requests (e.g. from the standstill control).
Childproof locks
The child safety lock prevents any unintentional releasing of the electric parking brake (EFB).
The Electronic Stability Program control unit ignores the request to release the electronic parking brake (EFB) through the electric parking brake switch, as long as circuit 15 (ignition ON) is not activated.
The electronic ignition lock control unit sends the status of circuit 15 over the chassis FlexRay to the Electronic Stability Program 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 detects the brake test through evaluation of the wheel speeds. If the Electronic Stability Program control unit detects a difference between the rotational speeds of the front and rear wheels, it activates the dynamometer test mode. 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 directly reads in the status of the electric parking brake switch. The Electronic Stability Program control unit then actuates the electric parking brake actuator motors for this purpose. The electronic parking brake (EFB) is applied or completely released. If the electronic parking brake (EFB) is tightened or released, the ESP® control unit transmits the request to switch the parking brake control message (red) on or off to the instrument cluster via the suspension FlexRay, electronic ignition lock control unit and the user interface CAN. The parking brake control message (red) then lights up or goes off on the instrument cluster.
To avoid any incorrect operations, temporary, or any unwanted operations are ignored.
Additional function requirements for automatically releasing electric parking brake (EFB)
- Engine running.
- The driver seat belt is applied or the driver's door is closed (Driver presence check).
The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal over the engine CAN, powertrain control unit and the chassis FlexRay to the Electronic Stability Program control unit.
The supplemental restraint system control unit sends the status of the driver seat belt over the vehicle dynamics CAN to the Electronic Stability Program control unit.
The left front door control unit sends the status of the driver front door over the interior CAN, electronic ignition lock control unit and the chassis FlexRay to the Electronic Stability Program control unit.
Automatically release electric parking brake (EFB)
As soon as a sufficient level of drive torque for driving off is applied to the wheels on the rear axle, the ESP® control unit completely releases the electronic parking brake (EFB).
The following conditions must be fulfilled here:
- Driver seat belt fitted:
- Transmission is in position D or R and accelerator pedal is operated.
- Gear shift from transmission position P to position D or R (on large uphill gradients with accelerator pedal also operated)
- Driver seat belt not fitted and driver front door closed:
- Gear shift out of transmission position P
- Vehicle speed before switching off the vehicle over 3 km/h
If reversing is intended, the rear-end door must be closed.
The Electronic Stability Program control unit evaluates the starting point by evaluating the following variables:
- Selector lever position
The steering column tube module control unit sends the current selector lever position over the chassis FlexRay to the Electronic Stability Program control unit.
- Drive range (transmission position)
The fully integrated transmission control unit sends information about the engaged gear range via drive train CAN, powertrain control unit and suspension FlexRay to the Electronic Stability Program control unit.
- Accelerator pedal position
The powertrain control unit sends information on the accelerator pedal position over the chassis FlexRay to the Electronic Stability Program control unit.
- Rear-end door status
The rear SAM control unit transmits the status of the rear-end door to the ESP® control unit via the interior CAN, electronic ignition lock control unit and the suspension FlexRay.
- 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 via the vehicle dynamics CAN to the Electronic Stability Program control unit.
- Engine torque
The CDI control unit or the ME-SFI [ME] control unit transmits information about the engine torque to the ESP® control unit via the engine CAN, powertrain control unit and the suspension FlexRay.
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 calculates the vehicle speed from the wheel speeds. The wheel speeds are detected by the rpm sensors. The Electronic Stability Program control unit directly reads in the signals from the rpm sensors.
The Electronic Stability Program control unit releases the electronic parking brake (EFB) through actuation of the electronic parking brake actuator motors on the rear brake calipers.
If the electronic parking brake (EFB) is not released due to an error, the instrument cluster displays the message "Release parking brake" and actuates the instrument cluster speaker to issue a warning tone.
Automatically engage electric parking brake (EFB)
If the vehicle has been brought to a standstill, the engine switched off and the driver wishes to get out of the vehicle, the Electronic Stability Program control unit automatically actuates the electronic parking brake actuator motors. The electronic parking brake (EFB) is activated.
The Electronic Stability Program control unit evaluates the following variables for this:
- Engine running status
The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal over the engine CAN, powertrain control unit and the chassis FlexRay to the Electronic Stability Program control unit.
- Status of driver seat belt
The supplemental restraint system control unit sends the status of the driver seat belt over the vehicle dynamics CAN to the Electronic Stability Program control unit.
- Status of driver front door
The left front door control unit sends the status of the driver front door over the interior CAN, electronic ignition lock control unit and the chassis FlexRay to the Electronic Stability Program 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 activates the electronic parking brake (EFB).
- Request through HOLD function:
- Request by Distance Pilot (with code EM4 (Driver Assistance Plus Package)):
The Distance Pilot DISTRONIC controller unit transmits the request "Activate EFB" to the ESP® control unit via the suspension FlexRay.
- Request by Parking Assist (with code EZ8 (PARKTRONIC)): The parking system control unit sends the "Activate electronic parking brake (EFB)" request over the chassis FlexRay to the Electronic Stability Program control unit.
The Electronic Stability Program control unit activates the electronic parking brake (EFB), when a system malfunction occurs or the power supply breaks down.
If the electronic parking brake (EFB) is activated, the parking brake control message (red) is shown on the instrument cluster.
The Electronic Stability Program control unit sends the status of the electronic parking brake (EFB) over the chassis FlexRay, electronic ignition lock control unit and the user interface CAN 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 CDI control unit or the ME-SFI [ME] control unit sends drivetrain operational signal over the engine CAN, powertrain control unit and the chassis FlexRay to the Electronic Stability Program control unit.
Operating the electric parking brake (EFB) switch can prevent the electric parking brake (EFB) from being activated.
Emergency braking
If the electronic parking brake (EFB) switch is operated and held while driving, the Electronic Stability Program control unit interprets this as a brake request and brakes the vehicle through the service brake. At the same time, the Electronic Stability Program control unit sends the status of the service brake over the chassis FlexRay, electronic ignition lock control unit and the interior CAN to the rear SAM control unit. The rear SAM control unit then activates the brake light actuation.
The Electronic Stability Program control unit then sends the request to issue a message over the chassis FlexRay, electronic ignition lock control unit and the user interface CAN to the instrument cluster. The instrument cluster issues the message "Release parking brake" and it actuates the instrument cluster speaker to output a warning tone.
Issuing of control and warning messages
The instrument cluster provides the driver with information on the function and status of the electronic parking brake (EFB).
The Electronic Stability Program control unit sends the corresponding requests over the chassis FlexRay, electronic ignition lock control unit and the user interface CAN to the instrument cluster.
The following displays can be shown on the instrument cluster:
- Parking brake control message (red)
- Parking brake warning message (yellow)
- Status/warning messages
The instrument cluster can also actuate the instrument cluster speaker to issue warning tones.
| Condition | Display | Actuation | Warning signal | Message (corresponding) |
|---|---|---|---|---|
| Electric parking brake (EFB) operated | Parking brake control message (red) | Permanently | - | - |
| Attempted release procedure for electric parking brake (EFB) at ignition OFF (child safety lock) | Parking brake control message (red) | Permanently | - | "Parking brake - release at ignition ON" |
| Conditions for automatic release not fulfilled OR braking with the electric parking brake (emergency brake application) | Parking brake control message (red) | Flashing | Intermittent tone | "Release parking brake" |
| Electric parking brake (EFB) malfunctioning or nonfunctional (permanent fault present, Service Required) | Parking brake warning message (yellow) | Permanently | - | "Parking brake - see operator's manual" |
| Parking brake warning message (yellow), parking brake control message (red) | Permanently | |||
| Parking brake control message (red) Parking brake warning message (yellow) | Flashing Permanently | |||
| Parking brake control message (red) | Flashing | |||
| Electric parking brake (EFB) defective, electric parking brake (EFB) nonfunctional | Parking brake warning message (yellow) Parking brake control message (red) | Permanently Flashing | - | "Parking brake inoperative" |
| Electrical function schematic for electric parking brake | PE42.20-P-2050-97ZGA | ||
| Overview of system components for electric parking brake | GF42.20-P-9998GWM |