Electric Parking Brake, Function - GF42.20-P-0001FR
Model 257, 290 up to model year 2021
Block diagram
Function requirements for electric parking Brake (EFB) in 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. To do so, the Electronic Stability Program control unit actuates the electronic parking Brake actuator motors directly.
The electronic parking Brake (EFB) switch can be manually actuated using the electric parking Brake switch or automatically. The clamping force of the electronic 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 display (yellow) and through text messages in the instrument cluster.
The electronic parking Brake can also be activated by external requests (e.g. from the standstill control system).
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 electronic 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 suspension 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 on 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 electronic parking Brake (EFB) manually
- Automatic release of electronic parking Brake (Comfort Go)
- Automatically engage electric parking Brake (EFB)
- Emergency braking
- Issuing of control and warning messages
Operate electronic parking Brake (EFB) manually
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 reads in the status of the electronic parking Brake switch directly. The Electronic Stability Program control unit then actuates the electronic parking Brake actuator motors. 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 indicator lamp (red) on or off over the suspension FlexRay, electronic ignition lock control unit and the user interface CAN 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 automatic release of electronic parking Brake (Comfort-Go)
- 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 suspension 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 suspension FlexRay to the Electronic Stability Program control unit.
Automatic release of electronic parking Brake (Comfort Go)
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 Electronic Stability Program control unit completely releases the electronic parking Brake (EFB).
The following conditions are taken into consideration here:
- Driver seat belt fitted:
- Transmission in position "D" or "R" and accelerator pedal operated
- Transmission in position "R" and trunk lid closed
- Driver seat belt not fitted and driver front door closed:
- Transmission in position "R" and trunk lid closed
- Change of transmission position from "P" or vehicle speed v > 3 km/h
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 suspension FlexRay to the Electronic Stability Program control unit.
- Drive position
The fully integrated transmission electric controller unit control unit sends information on the engaged drive range over the drive train CAN, powertrain control unit and the 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 suspension 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 suspension 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 over 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 suspension FlexRay to the Electronic Stability Program 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 calculates the vehicle speed from the wheel speeds. The wheel speeds are detected by the rpm sensors. The Electronic Stability Program control unit reads in the signals from the rpm sensors directly.
The Electronic Stability Program control unit releases the electronic parking Brake by actuating the electronic parking Brake actuator motors on the rear Brake calipers.
If a fault prevents the electronic parking Brake (EFB) from being released, the instrument cluster issues "Release parking brake" message and actuates the instrument cluster speaker to emit 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. To do so, the Electronic Stability Program control unit evaluates the following variables:
- 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 suspension 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 suspension FlexRay to the Electronic Stability Program control unit.
- Request to activate electronic parking Brake (EFB) through driver assistance system
- 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 (Distance Pilot DISTRONIC) or code 23P (Driving Assistance Package)) or with code P20 (Driving Assistance Plus Package)):
The Distance Pilot DISTRONIC controller unit or the Mercedes-Benz Intelligent Drive control unit sends the "Activate electronic parking Brake (EFB)" request over the suspension FlexRay to the Electronic Stability Program control unit.
- Request through Parking Assist (with code 235 (Parking Pilot with PARKTRONIC) or with code P44 (Parking Package)):
The parking system control unit sends the "Activate electronic parking Brake (EFB)" request over the suspension 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 if the power supply breaks down.
If the electronic parking Brake (EFB) is activated, the parking Brake indicator 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 suspension 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 the "Drive train operational" signal over the engine CAN, powertrain control unit and the suspension 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 switch is operated and held while driving, the Electronic Stability Program control unit interprets this to be a request to Brake and brakes the vehicle using the service brake. At the same time the Electronic Stability Program control unit sends the status of the service Brake over the suspension 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 sends the request to issue a message over the suspension FlexRay, electronic ignition lock control unit and the user interface CAN to the instrument cluster. The instrument cluster issues the "Release parking brake" message and actuates the instrument cluster speaker to emit 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 suspension 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 lamp (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 |
|---|---|---|---|---|
| Electric parking Brake (EFB) operated | Parking Brake indicator lamp (red) | Permanently | - | - |
| Electric parking Brake (EFB) malfunctioning or nonfunctional (permanent fault present, Service Required) | Parking Brake warning display (yellow)/parking Brake indicator lamp (red) | Continuously/flashing | - | Parking Brake "P" See operator's manual! |
| Electric parking Brake (EFB) defective, electric parking Brake (EFB) nonfunctional | Parking Brake warning indicator (yellow) | Flashing | - | Parking Brake inoperative! "P" |
| Attempted release procedure for electronic parking Brake (EFB) at ignition OFF (child safety lock) | Parking Brake indicator lamp (red) | Permanently | - | Parking brake! "P" To release switch on ignition! |
| Conditions for automatic release not fulfilled OR braking with the electric parking Brake (emergency Brake application) | Parking Brake indicator lamp (red) | Flashing | Bleep-interval | Parking brake! "P" Release brake! |
| Electrical function schematic for electric parking brake | PE42.20-P-2050-97XBA | ||
| Overview of system components for electric parking brake | GF42.20-P-9998FR |