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(Adaptive Brake (ABR), Function - GF42.47-P-0001GR)

MODEL 166 

up to model year 2016 

G14138714Courtesy of MERCEDES-BENZ USA

Block diagram 

Function requirements, general 

ADAPTIVE BRAKE, general 

ADAPTIVE BRAKE assists the driver in dangerous situations which occur suddenly, and thus enhances active safety.

To do so, the Electronic Stability Program control unit evaluates the data from the following components in order to detect the current driving situation:

ADAPTIVE BRAKE is available in 2 variants:

IMPORTANT There are no differences between the variants with respect to the ADAPTIVE BRAKE subfunctions described below.

The system is made up of the following subfunctions:

Function sequence for ESP® 

ESP® prevents the vehicle from breaking away when oversteering or understeering. It ensures that the vehicle does not deviate from the course specified by the driver (within physical limits). Brake forces are produced selectively at the individual wheels to correct any deviations. Furthermore, drive torque is reduced to increase the directional stability and road adhesion.

The Electronic Stability Program control unit processes the following measured quantities to determine the vehicle behavior:

Differentiation is made between the following intervention types:

Intervention in the case of oversteer 

If the vehicle begins to oversteer, brake pressure is built up at the outer front wheel. The resulting reduction in lateral force at the outer front wheel generates a yawing moment which counteracts the tendency of the vehicle to rotate inward. The vehicle speed decreases as a result of the brake force at the front wheel, which also enhances stability.

Intervention in the case of understeer 

If the vehicle understeers, the maximum possible lateral force at the front axle has been exceeded. In other words, the vehicle pushes via the front axle to the outer edge of the curve.

The resulting instability is counteracted by means of a reduction in drive torque and the following brake interventions at up to 3 wheels:

Depending on the brake force, a torque is generated which causes the vehicle to rotate inward with a simultaneous reduction in speed. This has a considerable stabilizing effect.

The Electronic Stability Program control unit sends a signal for drive torque reduction via chassis CAN 1 to the CDI control unit (with diesel engine) or ME-SFI [ME] control unit (with gasoline engine), which reduces the engine power accordingly.

A pending shift operation is suppressed for the duration of control intervention.

To this end, the Electronic Stability Program control unit sends a signal over chassis CAN 1 to the CDI control unit (with diesel engine) or ME-SFI [ME] control unit (with gasoline engine) which then sends the information over the drive train CAN to the fully integrated transmission control unit. The fully integrated transmission control unit suppresses the shift operation.

EBD function sequence 

The EBD [EBV] function supports the driving stability of the vehicle. EBD [EBV] is active during mid and high level vehicle decelerations during the brake actuation. EBD [EBV] is operational before the ABS is active and prevents the rear axle from overbraking. This is achieved by a brake pressure limitation at the rear axle as soon as the rpm sensors detect imminent overbraking of the rear axle.

Function sequence of exhaust test, dynamometer test mode 

For vehicle test purposes, the ADAPTIVE BRAKE can be set to dynamometer test mode if the workshop menu is activated via the instrument cluster and the engine is then started. ESP®, ABS and ASR are then switched to passive. The Electronic Stability Program warning lamp and the antilock brake system indicator lamp in the instrument cluster light up. In addition, a message is displayed in the multifunction display of the instrument cluster. The roller dynamometer mode can also be activated via Xentry Diagnostics.

ABS function sequence 

ABS prevents the wheels locking when braking and as a result maintains the steerability and directional stability and road adhesion during the vehicle deceleration.

If a locking wheel is detected by the Electronic Stability Program control unit based on signals from the rpm sensors, the brake pressure on the relevant wheel is reduced until the wheel begins to turn again.

Function sequence for ASR, ETS 

ASR and ETS prevent the drive wheels from spinning when driving. ASR and ETS also serve to provide improved directional stability and road adhesion for increased traction potential over the entire vehicle speed range. Spinning of the drive wheels is detected by the Electronic Stability Program control unit using the signals from the rpm sensors. Wheel spinning is countered by reduction of the drive torque.

To do so, the Electronic Stability Program control unit sends a signal to reduce the drive torque via chassis CAN 1 to the CDI control unit (with diesel engine) or ME-SFI [ME] control unit (with gasoline engine), which reduces the engine power accordingly.

A check is continuously performed to establish whether the drive torque specified by the driver via the accelerator pedal sensor can be permitted again, e.g. due to an improvement in road surface adhesion. The drive torque is transmitted to the opposite drive wheel, which is still moving, by means of targeted brake interventions on the spinning wheel.

BAS function sequence 

The BAS detects emergency braking situations based on rapid actuation of the brake pedal and, if necessary, increases the brake pressure in order to achieve maximum deceleration.

For this purpose, the Electronic Stability Program control unit evaluates the increase in pressure in the brake system and initiates an emergency stop if a certain triggering threshold is exceeded.

Function sequence for BAS PLUS, with CODE 233 (DISTRONIC PLUS), with CODE 237 (Active Blind Spot Assist), with CODE 238 (Active Lane Keeping Assist) 

BAS Plus increases the brake pressure depending on the speed of the brake pedal operation and the distance to the vehicle driving in front.

Function sequence for ESP® trailer stabilization (with CODE 550 (Trailer hitch)) 

The ESP® trailer stabilization detects rocking motion in the tractor/trailer combination based on the yawing vibrations caused in the tractor vehicle by the trailer.

If vehicle/trailer instability occurs, this is detected in the ADAPTIVE BRAKE by means of the sensor signals from the yaw rate, lateral and longitudinal acceleration sensor.

The Electronic Stability Program control unit receives this information via the vehicle dynamics CAN.

IMPORTANT The ESP® trailer stabilization engages more sensitively if a trailer hitch is installed at the factory. If the trailer hitches are retrofitted, the standard intervention ensures stabilization.

The ESP® trailer stabilization stabilizes the tractor/trailer combination by means of brake pressure requests on alternating sides of the front axle and, if necessary, slows down the tractor/trailer combination by reducing engine torque and by building up pressure at all wheels. Active vehicle/trailer stabilization does not change the critical speed.

Additional function requirements for the Hill Start Assist 

Hill Start Assist function sequence 

When starting off, the Hill-Start Assist prevents the vehicle from rolling back opposite the engaged gear range during the time it takes for the driver to change from the brake pedal to the accelerator pedal.

The function is triggered automatically, if when the vehicle is at a standstill an incline is detected through the yaw rate sensor for lateral and longitudinal acceleration which would cause rolling in the opposite direction to the gear range engaged. This information is sent to the Electronic Stability Program control unit over the vehicle dynamics CAN.

The Electronic Stability Program control unit reads in the signals from the brake light switch directly thereby enabling it to detect the status of the brake pedal. The electric parking brake control unit transmits the status of the electric parking brake via chassis CAN 1 to the Electronic Stability Program control unit.

The brake pressure applied by the driver is maintained in the brake system by the traction system hydraulic unit. Once the brake pedal is released and the accelerator pedal is pressed, the brake pressure is modulated based on the downslope torque, braking torque and drive torque. Once there is sufficient starting torque, the function is deactivated and the vehicle drives off. However, if the driver does not actuate the accelerator pedal, the pressure in the brake system is released after t = 1 s.

The Hill-Start Assist is terminated immediately if:

The Hill-Start Assist does not function if:

Additional function requirements for speed control during downhill driving 

Function sequence for speed control during downhill driving 

The downhill speed regulation serves to provide greater safety when driving on steep terrain. The corresponding menu in the instrument cluster can be used to set the relevant setting speed for the downhill speed regulation function, in a range of v = 4 km/h up to v = 18 km/h in increments of 2 km/h.

The system is activated via the Downhill Speed Regulation button in the lower control panel control unit. Activation is indicated by an LED in the Downhill Speed Regulation button.

The determined vehicle speed is now maintained in accordance with the speed setting (this is shown on the multifunction display of the instrument cluster).

During downhill driving, the set speed can be varied using the cruise control lever (S40) (with CODE (494) USA version) or the cruise control lever (S40/4) (without code (494) USA version).

The request to activate speed control during downhill driving is read in by the lower control panel control unit and sent via the center console switch LIN to the SAM control unit.

The SAM control unit sends the signal to the interior CAN. The electronic ignition lock control unit receives the signal and sends this information to the chassis CAN 1.

The Electronic Stability Program control unit receives the signal and regulates the required speed by means of brake interventions and corresponding requests to the engine management and the transmission control. If the driver accelerates the vehicle by pressing the accelerator pedal while the function is active, the downhill speed regulation switches to passive mode.

If the vehicle speed is v > 35 km/h when the accelerator pedal is not pressed, it is actively regulated to the configured setting speed. If the driver then accelerates the vehicle using the accelerator pedal during an active function to a speed of v > 35 km/h, the downhill speed regulation switches off automatically and the LED in the Downhill Speed Regulation switch goes out. In addition a message appears in the multifunction display of the instrument cluster and a warning tone sounds. If the speed regulation for downhill driving is switched off manually via the Downhill Speed Regulation button, likewise a message appears in the multifunction display of the instrument cluster. A warning tone does not sound in this case.

Additional function requirements for off-road program 

Function sequence for off-road program 

The function sequence for the off-road program is made up of the following subfunctions:

Function sequence for activation of off-road program 

Model 166 without CODE 430 (On & Offroad package):

The off-road program is activated by the off-road program button in the lower control panel control unit.

Activation is displayed by a light-emitting diode lighting up in the off-road program button. The off-road symbol also appears on the multifunction display of the instrument cluster.

The off-road program is deactivated by pressing the off-road program button again. The light-emitting diode in the off-road program button and the indicator in the multifunction display go out.

Model 166 with CODE 430 (On & Offroad package):

The off-road program is activated through the off-road package transmission mode controller in the off-road operating panel control unit.

The completed shift operation is indicated by an illuminated light-emitting diode.

Function requirements for deactivation of the off-road program:

Function sequence for adaptation of the threshold values 

Through activation of the off-road program:

The changes mentioned with regard to ESP®, ABS and ASR are dependent on the speed.

This means that the threshold values for an active off-road program match those of on-road mode as of a speed of approx. v = 50 km/h. If the vehicle decelerates to below a speed of approx. v = 50 km/h, the thresholds return to the off-road values.

Function sequence for engine torque support (with code 430 (On & Offroad package) 

If braking torque can no longer be applied for at least one wheel (wheel is stationary because there is no load on it) with the downhill speed regulation activated, off-road program activated and differential locks disengaged, brake pressure is built up actively at the wheels with traction through the Electronic Stability Program control unit.

The engine torque support is active at a speed of v = 1 km/h to v = 18 km/h.

Function sequence for influencing locks (with CODE 430 (On & Offroad package)) 

In the following driving situations the activated locks are immediately released:

The request to disengage the locks occurs via the Electronic Stability Program control unit, which transmits a corresponding signal via chassis CAN 1 and the drive train CAN with the ME-SFI [ME] control unit interface (with gasoline engine) or CDI control unit (with diesel engine) to the transfer case control unit. The transfer case control unit disengages the activated lock between front and rear axle.

Function requirements for dry braking 

Dry braking function sequence 

The dry braking function enhances the performance capability of the front axle brake under wet conditions. The brake pads are applied cyclically for a short time (approx. t = 0.5 s) with a brake pressure p = 1 bar to remove the film of water from the brake disk. This improves the response time of the brake.

IMPORTANT In order to adapt the calculated triggering threshold of the accelerator pedal gradient to driver behavior, a learning algorithm is implemented which places the driver in the category "normal driver" or "hectic driver" on the basis of the average rate at which the accelerator pedal is released.

IMPORTANT The status of the windshield wiper system is transmitted by the SAM control unit via interior CAN to the electronic ignition lock control unit and on to the Electronic Stability Program control unit via chassis CAN 1.

Function sequence for precharging dependent on accelerator pedal operation 

Upon detection of a possible emergency braking situation, the brake pads are brought into contact with the brake disks. The clearance between the brake pad and brake disk is thus compensated before the driver operates the brake.

The response time of the brake is improved and a shorter braking distance can be achieved.

Emergency braking is detected from the release gradient of the accelerator pedal, which is formed from the accelerator pedal position. If a rapid release of the accelerator pedal is detected, the system assumes that the driver intends to brake. The function is activated and a brake pressure of p = 2 to 3 bar is requested.

Function sequence for HOLD function 

The HOLD function assists the driver during waiting times in traffic and when starting off on a hill. The HOLD function is activated by briefly and quickly depressing the brake pedal when the vehicle is stationary. Successful activation of the HOLD function is indicated in a status line in the instrument cluster.

The HOLD function can be activated if:

If the driver releases the brake pedal, an incline-dependent hold pressure is set and maintained until the driver presses the brake pedal again or drives off. Pressure reduction when starting off is performed by the standstill control depending on the respective situation.

The HOLD function is deactivated automatically if:

Function sequence for ASR and ESP® passive switching 

The ASR and ESP® functions can be switched to passive mode via the ESP OFF button. The ESP OFF button status is read in over a direct line by the upper control panel control unit and the signals are forwarded over the center console switch LIN to the SAM control unit, over the interior CAN to the electronic ignition lock control unit and over the chassis CAN 1 to the Electronic Stability Program control unit. If the system is switched passive, the Electronic Stability Program warning lamp lights up in the instrument cluster. The control thresholds are raised in the case of passive switching.

IMPORTANT ABS cannot be deactivated. ESP® is always active during a brake application.

Additional function requirements for flashing adaptive brake lights (except CODE 494 (USA version)) 

Function sequence for flashing adaptive brake lights (except CODE (494) USA version) 

In the event of an emergency stop, the Electronic Stability Program control unit sends a corresponding signal via chassis CAN 1 and the interior CAN with the electronic ignition lock control unit interface to the SAM control unit.

The SAM control unit actuates the left rear lamp unit, the right rear lamp unit and the center brake lamp with a flashing frequency of f = 5 Hz for the duration of the signal (min. t = 1 s). If the vehicle comes to a standstill from a speed > 70 km/h (not urban traffic), the brake lights and the additional brake lamp are permanently actuated again. In addition, the automatic hazard warning flasher function is activated. If the vehicle then exceeds a speed of 10 km/h again, the hazard warning system are automatically switched off again.

Function sequence - Fail boost 

The fail boost function ensures brake boosting. It is activated if the pneumatic brake booster cannot adequately support driver braking because of a system error in the vacuum supply.

The system error in the vacuum supply is displayed in the instrument cluster by the brake force distribution warning lamp. The failure of the pneumatic brake booster is detected via the brake vacuum sensor, which is integrated in the pneumatic brake booster.

The fail boost function performs hydraulic brake boosting using a suitable boost factor and actuates the solenoid valves and the traction system hydraulic unit in the ESP® system for this accordingly. If this fault profile exists, check the corresponding fault entry via diagnosis in the Electronic Stability Program control unit and proceed according to the repair instructions.

Function sequence - Over boost 

Like the fail boost function, the over boost function ensures brake boosting. The over boost function is activated if the pneumatic brake booster can no longer adequately support driver braking because of a brief sub-optimal vacuum level. Unlike fail boost, over boost represents a normal operating state. There is no system error in the vacuum supply.

This briefly reduced vacuum level operating state can occur, for example, in the following cases:

The overboost function performs hydraulic brake boosting using a suitable boost factor and actuates the solenoid valves and the traction system hydraulic unit in the ESP® system for this accordingly.

Function sequence for standstill control (SSC) 

The standstill control monitors the braking driver assistance systems DISTRONIC PLUS (with ADAPTIVE BRAKE premium system (with CODE 233 (DISTRONIC PLUS)) and HOLD function below a speed of 3 km/h until the vehicle has come to a safe standstill. Within this vehicle speed range, the SSC is responsible for the transfer to a safe state when a securing event occurs.

When the vehicle is at a safe standstill, the rolling monitoring function of the SSC is requested by the driver assistance systems. If vehicle rolling is detected, the brake pressure is increased until the vehicle is stationary again. In the case of vehicles with Premium ADAPTIVE BRAKE system (with CODE 233 (DISTRONIC PLUS)), a leakage compensation is also active during the safe standstill. If the brake pressure measured by means of the circuit pressure sensors drops relative to the specified pressure request of the SSC, the specified pressure of the SSC is restored by means of an active pressure buildup.

Securing the vehicle by means of the SSK is necessary if the following events occur:

Door contact plausibility check 

The plausibility check detects any faults along the signal path from the left front door microswitch first detent position or the right front door microswitch first detent position (depending on global national coding for right-hand or left-hand drive vehicle), read in by the left front door control unit or the right front door control unit and sent over the interior CAN and chassis CAN 1, with the electronic ignition lock control unit interface to the Electronic Stability Program control unit. If, as the result of an electrical or mechanical fault, "Driver door closed" is detected by mistake although the driver door is open, this is detected by the door contact plausibility check in the SSC and a corresponding fault is stored in the Electronic Stability Program control unit.

SSK deactivation 

Deactivation of the SSK is signaled internally in the Electronic Stability Program control unit and externally over the chassis CAN 1. Activation of the driver assistance systems is no longer possible. Securing of the vehicle is additionally requested immediately if the SSK is deactivated and a driver assistance system is active.

Sliding 

When the vehicle is stationary, the SSK monitors whether the vehicle is sliding. Activation of the driver assistance systems is not permitted during this time. The active driver assistance systems must deactivate when the brake pedal is depressed and the vehicle is sliding.

Securing the vehicle 

The vehicle is secured by the comfort securing system of the electric parking brake, which is prompted to lock by the SSC. For this purpose, the Electronic Stability Program control unit sends a signal via the chassis CAN 1 to the electric parking brake control unit. The vehicle is secured after the locking request has been implemented and the feedback signal to confirm that the service brake is applied has been sent from the electric parking brake control unit to the Electronic Stability Program control unit. The existing brake pressure at the wheels is reduced and the SSC becomes inactive.

If the close request is not implemented by the electric parking brake within a defined time or the electric parking brake signals a system fault to the SSC, the electric parking brake is detected as being defective and the safety strategy becomes active.

Safety strategy, request engage "P" or Emergency-P path 

The safety strategy is implemented via the intelligent servo module for DIRECT SELECT. The Electronic Stability Program control unit sends a request to engage gear range "P" via chassis CAN 1 and drive train CAN with the interface CDI control unit (with diesel engine) or ME-SFI [ME] control unit (with gasoline engine) to the intelligent servo module for DIRECT SELECT control unit. The vehicle is secured once the intelligent servo module for DIRECT SELECT has engaged gear range "P" and following feedback to the Electronic Stability Program control unit. The existing brake pressure at the wheels is reduced and the SSC becomes inactive.

If the intelligent servo module for DIRECT SELECT does not signal engagement of gear range "P" within a defined time, the Emergency-P function of the electronic ignition lock control unit forces gear range "P" to be engaged.

To do so, the electronic ignition lock control unit also receives the request for engaging gear range "P" from the Electronic Stability Program control unit over the chassis CAN 1 and sends a request itself to the intelligent servo module for DIRECT SELECT. If the electronic ignition lock control unit does not receive feedback from the intelligent servo module for DIRECT SELECT within a defined time, the Emergency-P path is energized by the electronic ignition lock control unit after being enabled by the intelligent servo module for DIRECT SELECT and engagement of gear range "P" is forced by a spring mechanism in the intelligent servo module for DIRECT SELECT.

Steer Assist function sequence 

The steering assistance function helps the driver to achieve an optimum steering reaction in critical driving situations. Steering assistance is provided with the aid of the electric power steering control unit and Electronic Stability Program control unit.

The following functions are performed here:

The current vehicle status is sensed by the Electronic Stability Program control unit. If necessary, chassis CAN 1 and chassis CAN 2 with the SAM control unit interface forward the message "steering assistance request" to the electrical power steering control unit, which actuates the electric power steering actuator motor accordingly.

Additional function requirements for Crosswind Assist, model 166.8 

Function sequence for Crosswind Assist, model 166.8 

The Crosswind Assist function assists the driver in the event of strong crosswinds and minimizes the vehicle's yaw response and the track offset. The yaw rate sensor for lateral and longitudinal acceleration records the movement of the vehicle in the event of quickly changing winds and sends the signals to the Electronic Stability Program control unit over the vehicle dynamics CAN. The Electronic Stability Program control unit also processes the steering wheel angle from the steering wheel angle sensor via chassis CAN 1, which is read in by the steering column tube module control unit, the toothed rack position from the electrical power steering control unit, the wheel speeds and the brake pressures.

After processing the signals, the Electronic Stability Program control unit regulates a one-sided brake intervention on the front and rear axle, thereby generating a yaw motion, which counteracts the crosswind.

System fault display function sequence 

The driver is informed about the system status and about faults by the following displays:

If the Electronic Stability Program control unit fails, basic braking without ABS is always available.

IMPORTANT The status of the brake fluid level switch is read in by the SAM control unit and sent to the instrument cluster via the interior CAN.

  Electrical function schematic for Adaptive Brake (ABR)   PE42.47-P-2050-97NAA
  Overview of system components, Adaptive Brake (ABR)   GF42.47-P-9997GR 
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