Electric Parking Brake, Function - GF42.20-P-0001FH
Model 238
Up To Model Year 2021
Function requirements - electric parking brake (EFB), general
- No undervoltage or overvoltage
Electronic parking brake (EFB), general
The electronic 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 electronic 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 monitor lamp (red), the parking brake warning indicator (yellow) and through text messages in the instrument cluster.
The electronic parking brake (EFB) can also be activated through external requests (e.g. from the standstill control).
Child safety lock
The child safety lock prevents any unintentional releasing of the electronic 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 electronic 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 electronic parking brake switch several times to gradually increase the clamping force of the electronic parking brake (EFB).
The electronic parking brake (EFB) includes the following subfunctions:
- Operate electronic parking brake (EFB)
- Automatically release electronic parking brake (EFB)
- Automatically engage electronic parking brake (EFB)
- Emergency braking
- Issuing of control and warning messages
Operate electronic parking brake (EFB)
The electronic parking brake (EFB) can be manually operated using the electronic parking brake (EFB) switch. Press electronic parking brake (EFB) switch: The EFB is applied. Pull electronic 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 applied or released, the Electronic Stability Program control unit sends the request to switch the parking brake monitor lamp (red) on or off over the chassis FlexRay, electronic ignition lock control unit and the user interface CAN to the instrument cluster. The parking brake monitor 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 electronic 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 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 electronic parking brake (EFB)
As soon as a sufficient level of drive torque is applied to the wheels on the rear axle, to enable it to drive off, the Electronic Stability Program control unit completely releases the electronic parking brake (EFB).
The following conditions must be fulfilled here:
- Driver seat belt fitted:
- Transmission 716:
- Forward or reverse gear engaged and accelerator pedal operated
- Transmission 725:
- Transmission in position D or R and accelerator pedal operated
- Gear shift from transmission position P to position D or R (on large uphill gradients with accelerator pedal also operated)
- Transmission 716:
- Driver seat belt not fitted and driver front door closed:
- Transmission 716:
- Vehicle speed before switching off the vehicle over 3 km/h
- Transmission 725:
- Gear shift out of transmission position P
- Vehicle speed before switching off the vehicle over 3 km/h
- Transmission 716:
If reverse travel is intended, the trunk lid must be closed.
The Electronic Stability Program control unit evaluates the starting point by evaluating the following variables:
- Forward or reverse gear engaged (transmission 716)
The powertrain control unit sends information on the engaged gear over the chassis FlexRay to the Electronic Stability Program control unit.
- Selector lever position (transmission 725)
The steering column tube module control unit sends the current selector lever position over the chassis FlexRay to the Electronic Stability Program control unit.
- Gear range (transmission position) (transmission 725)
The fully integrated transmission control unit sends information about the engaged gear range via drive train CAN, powertrain control unit and chassis 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.
- Status of trunk lid
The rear SAM control unit sends the status of the trunk lid over the interior CAN, electronic ignition lock control unit and the chassis FlexRay to the Electronic Stability Program 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 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 sends information about the engine torque over the drive train CAN, powertrain control unit and the chassis FlexRay to the Electronic Stability Program control unit.
On uphill gradients over 5 % the engine torque is also evaluated. The electronic 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, as a consequence, the electronic parking brake (EFB) is not released, the instrument cluster displays a Release parking brake message and actuates the instrument cluster speaker to issue a warning tone.
Automatically engage electronic 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 electronic 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 Distance Pilot (with code 239 (DISTRONIC Distance Pilot) or code 23P (Driving Assistance Package)):
The DISTRONIC Distance Pilot controller unit or the Intelligent Drive control unit sends the "Activate electronic parking brake (EFB)" request over the chassis FlexRay to the Electronic Stability Program control unit.
- Request through Park Assist (with code 235 (PARKTRONIC Parking Pilot)):
The parking system control unit sends the "Activate electronic parking brake (EFB)" request over the chassis FlexRay to the Electronic Stability Program control unit.
- Request through HOLD function:
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 monitor lamp (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 electronic 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 electronic parking brake (EFB) switch can prevent the electronic 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 following 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 indicator (red)
- Parking brake warning indicator (yellow)
- Status/warning messages
The instrument cluster can also actuate the instrument cluster speaker to issue warning tones.
| CONDITION | Display | Actuation | Warning signal | Message |
|---|---|---|---|---|
| Electronic parking brake (EFB) operated | Parking brake indicator (red) | Permanently | - | - |
| Attempted release procedure for electronic parking brake (EFB) at ignition OFF (child safety lock) | Parking brake indicator (red) | Permanently | - | Release parking brake at ignition ON |
| Conditions for automatic release not fulfilled OR braking with the electric parking brake (emergency brake application) | Parking brake indicator (red) | Flashing | Intermittent tone | Release parking brake |
| Electronic parking brake (EFB) malfunctioning or nonfunctional (permanent fault present, Service Required) | Parking brake warning indicator (yellow) | Permanently | - | See operator's manual for parking brake |
| Parking brake warning indicator (yellow), parking brake monitor lamp (red) | Permanently | |||
| Parking brake indicator (red) Parking brake warning indicator (yellow) | Flashing Permanently | |||
| Parking brake indicator (red) | Flashing | |||
| Electronic parking brake (EFB) defective, electronic parking brake (EFB) nonfunctional | Parking brake warning indicator (yellow) Parking brake indicator (red) | Permanently Flashing | - | Parking brake INOPERATIVE |
| Electrical function schematic for electric parking brake | PE42.20-P-2050-97DCA | ||
| Overview of system components for electric parking brake | GF42.20-P-9998FH |