PRE-SAFE (R), Function - GF91.40-P-0001LF

Model 217, 222 

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Terminal 15 ON
• No overvoltage or undervoltage
• "Engine running" or "Drive train operational" signal set (except with seat belt adjustment function)

The electronic ignition lock control unit sends the status of circuit 15 over the chassis FlexRay to the Electronic Stability Program control unit.

The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or "Drive train operational" signal over the engine CAN, powertrain control unit and chassis FlexRay to the Electronic Stability Program control unit.

PRE-SAFE, general 

The preventive occupant protection system PRE-SAFE can recognize critical driving situations in advance and activate safety systems that reduce the risk of injury to the vehicle occupants as a precautionary measure if necessary. In order to do this, PRE-SAFE permanently evaluates sensor data from systems such as the Electronic Stability Program (ESP®) and the Brake Assist System PLUS (BAS PLUS), and can therefore detect excessive understeer or oversteer and emergency braking, for example. If a critical driving situation is recognized, corresponding measures can be started within fractions of a second. These measures allow the seat belts and airbags to provide their full protective effect in the event of a collision.

The PRE-SAFE function is activated by the Electronic Stability Program control unit.

The PRE-SAFE function includes the following subfunctions:

• Function sequence for sensing the vehicle status 
• Function sequence for front reversible tensioning retraction 
• Function sequence for rear reversible belt tensioner (With Code 305 (Rear PRE-SAFE)) 
• Function sequence for seat belt adaptation 
• Function sequence for positioning front passenger seat (model 222 With Code 275 (Memory Package), model 217) 
• Function sequence for positioning rear seats (With Code 223 (Electrically adjustable rear bench seat)) 
• Function sequence for adjusting seat contour (With Code 432 (Left and right dynamic multicontour seat) or code 406 (Multicontour seat in the rear)) 
• Function sequence for closing side windows 
• Function sequence for closing the panoramic sliding sunroof (With Code 413 (Panoramic sliding sunroof)) 
• Function sequence for display of fault messages 
• Function sequence for terminating PRE-SAFE functions 

Function sequence for sensing the vehicle status 

The current vehicle status is defined by the Electronic Stability Program control unit by evaluating the following variables:

• Wheel speed
• Natural dynamics of the vehicle (yaw speed, lateral acceleration and longitudinal acceleration)
• Steering angle

Detailed information on how these variables are acquired can be found in a separate function description.

This applies to vehicles up to model year 2018: 

The Electronic Stability Program control unit also evaluates the following signals from different driver assistance systems:

• "Autonomous brake application" signal and relative speed to the opposing object:

  The radar sensors control unit (with code P20 (Driving Assistance Plus Package)) transmits the "Autonomous brake application" signal or the relative speed to the opposing object to the Electronic Stability Program control unit via the suspension FlexRay.

• "Autonomous brake application" signal:

  The COLLISION PREVENTION ASSIST controller unit (with code 258 (COLLISION PREVENTION ASSIST PLUS)) transmits the "Autonomous brake application" signal to the Electronic Stability Program control unit via the peripherals CAN, electronic ignition lock control unit and suspension FlexRay.

The Electronic Stability Program control unit differentiates the following critical statuses:

• Emergency braking: Fast brake-pedal operation, which indicates a startled response by the driver.
• Panic braking: The driver's deceleration request is significantly higher than the physically possible vehicle deceleration on a slippery road (e.g. aquaplaning, ice or snow). Strong interventions of the anti-lock braking system (ABS).
• Strong oversteer: Swerving of rear end combined with strong ESP® stabilization interventions.
• Strong understeer: Vehicle pushes for a certain time over the front wheels. Strong ESP® stabilization interventions.
• Critical steering movements: Rapid steering movements at high speeds (v > 140 km/h) that indicate a startled reaction from the driver, making it highly likely that the driver will not be able to cope with this situation.
• Strong brake application support through BAS PLUS (with code 233 (DISTRONIC PLUS)): Strong support of brake application initiated by the driver in response to a recognized danger of collision in longitudinal traffic based on a radar-supported assessment of the surroundings.
• Autonomous brake application through the PRE-SAFE® brake (with code 233 (DISTRONIC PLUS)): Vehicle deceleration by the PRE-SAFE® brake in response to a recognized danger of collision in longitudinal traffic based on a radar-supported assessment of the surroundings.
• Front collision object detection (with CODE 233 (DISTRONIC PLUS)): Detection of an imminent frontal impact (under certain conditions) based on a radar-supported assessment of the surroundings.
• Rear collision object detection (with code 253 (Rear collision warning and protection system)): Detection of an imminent rear impact (under certain conditions) based on a radar-supported assessment of the surroundings.
• Autonomous course correction through Active Blind Spot Assist (with CODE 237 (Active Blind Spot Assist)): Pronounced, course-correcting brake intervention with registered risk of a side collision with vehicles in blind spot based on a radar-supported assessment of the surroundings.

The triggering threshold for the PRE-SAFE functions is increased if the ESP® has been manually switched to passive via the menu on the instrument cluster. The instrument cluster transmits the status of the ESP® via the user interface CAN, the electronic ignition lock control unit and the chassis FlexRay to the Electronic Stability Program control unit.

This applies to vehicles as of model year 2018: 

In vehicles with code 23P (Driving Assistance Package) or code P20 (Driving Assistance Plus Package) or code 258 (Active Brake Assist), the Electronic Stability Program control unit also evaluates active assistance system interventions and collision-critical warnings.

The Mercedes-Benz Intelligent Drive control unit (with code 23P (Driving Assistance Package) or code P20 (Driving Assistance Plus Package)) transmits the appropriate signals to the Electronic Stability Program control unit via the suspension FlexRay.

The Active Brake Assist controller unit (with code 258 (Active Brake Assist)) transmits the appropriate signals to the Electronic Stability Program control unit via the peripherals CAN, electronic ignition lock control unit and suspension FlexRay.

The PRE-SAFE® system is triggered for the following scenarios:

• Emergency braking: Fast brake pedal operation, which indicates a startled response by the driver.
• Maximum full-stop braking: the driver's deceleration request is significantly higher than the physically possible vehicle deceleration (e.g. aquaplaning, ice or snow). Strong interventions of the anti-lock braking system (ABS).
• Strong oversteer: Swerving of rear end combined with strong ESP® stabilization interventions.
• Strong understeer: Vehicle pushes for a certain time over the front wheels. Strong ESP® stabilization interventions.
• Crosswind stabilization: Drifting from the specified lane, connected with strong ESP® stabilization interventions.
• Critical steering movement: rapid steering movements at fast speed that indicate a startled response from the driver and imply that the driver is unable to cope with this situation.
• Secondary accident: occurrence of another accident after an initial accident.

Additionally in vehicles with code 23P (Driving Assistance Package) or code P20 (Driving Assistance Plus Package) or code 258 (Active Brake Assist):

• Strong brake application support through BAS PLUS: Strong support of brake application initiated by the driver in response to a recognized danger of collision in longitudinal traffic based on radar-supported assessment of the surroundings.
• Autonomous brake application by the PRE-SAFE® brake: Vehicle deceleration with detected risk of collision in linear traffic by the PRE-SAFE® brake based on radar-assisted evaluation of the surroundings.
• Autonomous course correction by the Blind Spot Assist: Significant, course-correcting intervention by the brake system in the event of a registered risk of a side collision with vehicles in the blind spot based on radar-assisted evaluation of the surroundings.
• Collision object detection at front/rear/side: detection of an imminent collision based on radar-assisted evaluation of the surroundings.

The triggering threshold for the PRE-SAFE® functions is modified depending on the following variables:

• ESP® mode
• Transmission mode

The head unit transmits the request for the selected ESP® mode and the selected transmission mode via the user interface CAN, the electronic ignition lock control unit and the chassis FlexRay to the Electronic Stability Program control unit.

Additional function requirement for front reversible emergency tensioning retraction 

• Front seat belt applied

The Supplemental Restraint System control unit directly reads in the status of the driver seat belt buckle switch and the front passenger seat belt buckle switch, and transmits these to the reversible belt tensioner via the user interface CAN.

Function sequence for front reversible tensioning retraction 

The reversible emergency tensioning retractors reduce any seat belt slack in hazardous situations by tensioning the seat belts using an electric motor. The driver and the front passenger are held in position in order to optimize the protective effect of the conventional restraint equipment. Depending on the situation, the belt strap of the seat belt is tightened with varying force or speed. After the PRE-SAFE measure, the belt strap of the seat belt is slackened again (unless a roll-over has occurred).

The Electronic Stability Program control unit transmits information about the PRE-SAFE status and the PRE-SAFE stage via the chassis FlexRay, the electronic ignition lock control unit and the user interface CAN to the reversible emergency tensioning retractors. The supplemental restraint system control unit sends the crash signal (in the event of a rollover) via user interface CAN to the reversible emergency tensioning retractors. In order to tension the seat belt, the respective reversible emergency tensioning retractor actuates an integrated actuator motor.

Additional function requirements for rear reversible belt tensioner (With Code 305 (Rear PRE-SAFE)) 

• Rear seat belt applied

The rear SAM control unit reads in the status of the respective rear belt buckle switch directly and sends it via interior CAN to the active belt buckle control unit.

Function sequence for rear reversible belt tensioner (With Code 305 (Rear PRE-SAFE)) 

The active belt buckle can be adjusted in height according to the situation whereby it can move to various positions. To reduce the present seat belt slack in dangerous situations, it is moved from the default position to the PRE-SAFE position. The occupants are held in place in the seats in order to optimize the protective effect of the conventional restraint equipment. Depending on the situation, the belt strap of the seat belt is tightened with varying force or speed by adjusting the belt buckle position. After the PRE-SAFE measure is complete, a reversing procedure is started to reduce the increased belt tension (unless a roll-over has occurred).

The supplemental restraint system control unit transmits the crash signal (in the event of a rollover) over the user interface CAN, electronic ignition lock control unit and interior CAN to the active belt buckle control unit. The Electronic Stability Program control unit sends information about the PRE-SAFE status and the PRE-SAFE stage over the chassis FlexRay, electronic ignition lock control unit and interior CAN to the active belt buckle control unit. The active belt buckle control unit then actuates the active belt buckle motors directly.

Additional function requirements for seat belt adjustment 

• Function in the COMAND controller unit (up to model year 2018) or in the head unit (as of model year 2018) activated
• PRE-SAFE has not been activated

The COMAND controller unit (up to model year 2018) or the head unit (as of model year 2018) transmits the status of the seat belt adjustment function to the reversible belt tensioner via the user interface CAN and, in vehicles with code 305 (Rear PRE-SAFE), this status is also sent to the active seat belt buckle control unit via the user interface CAN, electronic ignition lock control unit and interior CAN.

Function sequence for seat belt adaptation 

The seat belt adjustment function reduces the existing seat belt slack of the front seats and the outer rear seats by tensioning the seat belts using an electric motor. The function is triggered when the belt lock tongue is inserted into the respective belt buckle. The insertion of the belt tab of the seat belt into the belt buckle is recorded via the status of the respective belt buckle switch.

Front seats: 

The supplemental restraint system control unit reads in the status of the respective seat belt buckle switch directly and transmits this via the user interface CAN to the reversible emergency tensioning retractors.

In order to tension the seat belt, the respective reversible emergency tensioning retractor actuates an integrated actuator motor. This tightens the belt strap at a constant speed until the seat belt slack has been reduced.

Rear seats (With Code 305 (Rear PRE-SAFE)): 

The rear SAM control unit reads in the status of the respective rear belt buckle switch directly and sends it via interior CAN to the active belt buckle control unit. The active belt buckle control unit actuates the rear seat active belt buckle motor directly. The active belt buckle is moved from the extended position to the default position and the seat belt slack is reduced.

Additional function requirements for positioning front passenger seat (model 222 With Code 275 (Memory Package), model 217) 

• Front passenger seat occupied
• Seat adjustment normalized

The supplemental restraint system control unit sends the status of the front passenger seat occupied recognition over the user interface CAN, electronic ignition lock control unit and interior CAN to the front passenger seat control unit.

Function sequence for positioning front passenger seat (model 222 With Code 275 (Memory Package), model 217) 

In order to optimize the protective effect of the conventional restraint equipment, the front passenger seat is moved into a position that is favorable from a safety point of view before a potential accident. The Electronic Stability Program control unit sends information about the PRE-SAFE status and the request for PRE-SAFE adjustment over the chassis FlexRay, electronic ignition lock control unit and interior CAN to the front passenger seat control unit. Any memory or manual setting that may be active is aborted.

Depending on the current seat position, the following adjustments are made:

• Backrest inclination
• Seat height
• Seat fore/aft position
• Seat inclination

The PRE-SAFE setting continues until

• The target position is reached (front passenger seat in optimum position)
• The impact occurs
• The PRE-SAFE situation ends

The PRE-SAFE setting of the front passenger seat can be canceled at any time by making manual adjustment requests. The front passenger seat does not automatically move back to its position prior to the PRE-SAFE situation, but has to be manually adjusted.

Seat adjustment if the front passenger is not wearing his/her seat belt:

The system moves the seat into a position that is adapted to the unsafe conditions. The supplemental restraint system control system reads in the status of the front passenger seat belt buckle switch directly and transmits this via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the front passenger seat control unit.

Detailed information on how to adjust the front passenger seat can be found in a separate function description.

Additional function requirements for positioning rear seats (With Code 223 (Electrically adjustable rear bench seat)) 

• Seat adjustment normalized

Function sequence for positioning rear seats (With Code 223 (Electrically adjustable rear bench seat)) 

In order to optimize the protective effect of the conventional restraint equipment, the outer rear seats are moved into a position that is favorable from a safety point of view before a potential accident. The Electronic Stability Program control unit sends information about the PRE-SAFE status and the request for PRE-SAFE adjustment over the chassis FlexRay, electronic ignition lock control unit and interior CAN to the rear seat control units. Any memory or manual setting that may be active is aborted.

Depending on the current seat position, the following adjustments are made:

• Head restraint inclination
• Backrest inclination
• Seat cushion inclination
• Leg rest inclination (with code 453 (Rear reclining seats))

The PRE-SAFE setting continues until

• The target position is reached (rear seats in optimum position)
• The impact occurs
• The PRE-SAFE situation ends

The PRE-SAFE setting of the rear seats can be canceled at any time by making manual adjustment requests. The rear seats do not automatically move back to their position prior to the PRE-SAFE situation, but have to be manually adjusted.

Seat adjustment if occupants are not buckled up:

The system moves the seat into a position that is adapted to the unsafe conditions. The rear SAM control unit reads in the status of the respective rear belt buckle switch directly and sends it via interior CAN to the right rear seat control unit or to the left rear seat control unit.

Detailed information on how to adjust the rear seats can be found in a separate function description.

Additional function requirements for adjusting seat contour (With Code 432 (Left and right dynamic multicontour seat) or code 406 (Multicontour seat in the rear)) 

• Seat belt applied

Model 217, 222

with code 432 (Left and right dynamic multicontour seat)

The supplemental restraint system control unit reads in the status of the respective seat belt buckle switch directly, and transmits this via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the left front multicontour seat control unit or the right front multicontour seat control unit.

Model 217, 222

with code 406 (Rear multicontour seat)

The rear SAM control unit reads in the status of the respective rear belt buckle switch directly and sends it via interior CAN to the left rear multicontour seat control unit or to the right rear multicontour seat control unit.

Function sequence for adjusting seat contour (With Code 432 (Left and right dynamic multicontour seat) or code 406 (Multicontour seat in the rear)) 

In order to optimize the protective effect of the conventional restraint equipment, the seat contour is adjusted before a potential accident using PRE-SAFE.

The Electronic Stability Program control unit sends information about the PRE-SAFE status and the request for PRE-SAFE adjustment over the chassis FlexRay, electronic ignition lock control unit and interior CAN to the following control units:

• Left front multicontour seat control unit
• Right front multicontour seat control unit
• Left rear multicontour seat control unit (with code 406 (Rear multicontour seats))
• Right rear multicontour seat control unit (with code 406 (Rear multicontour seats))

The following settings are made:

• Inflating the side inserts (occupants are held in a central position in the seat)
• Deflating the lumbar support bladders (occupants sit lower in the seat)

The PRE-SAFE setting continues until

• Specified pressure reached in the side inserts
• The impact occurs
• The PRE-SAFE situation ends

The PRE-SAFE setting of the seat contour can be canceled at any time by making manual adjustment requests. Once the PRE-SAFE situation has ended, the inflation status of the side inserts and lumbar support bladders is returned to its respective initial status.

Detailed information on how to adjust the seat contour can be found in a separate function description.

Additional function requirements for closing the side windows 

• Power windows normalized

Function sequence for closing side windows 

Closing the side windows apart from a small gap is intended to ensure that no objects can penetrate into the vehicle interior and no body parts (e.g. arms) of the occupants can protrude from the vehicle in the event of a potential accident. This also allows the smoke particles generated by the pyrotechnical restraint equipment to disperse quickly.

The Electronic Stability Program control unit sends information about the PRE-SAFE status and the request for PRE-SAFE adjustment over the chassis FlexRay, electronic ignition lock control unit and interior CAN to the following control units:

• Rear control unit (model 217)
• Left front door control unit
• Right front door control unit
• Left rear door control unit (model 222)
• Right rear door control unit (model 222)

Any automatic opening or manual setting that is active is aborted. The automatic reversing function is active when closing the side windows using PRE-SAFE. If required, the closing process is reversed.

The PRE-SAFE setting continues until

• The side windows reach the PRE-SAFE position
• The impact occurs

The closing of the respective side window by PRE-SAFE can be interrupted at any time by a manual adjustment request. Following the PRE-SAFE situation, the side windows must be manually moved back into the desired position.

Detailed information on how to control the side windows can be found in a separate function description.

Additional function requirements for closing panoramic sliding sunroof (With Code 413 (Panoramic sliding sunroof)) 

• Panoramic sliding sunroof normalized

Function sequence for closing the panoramic sliding sunroof (With Code 413 (Panoramic sliding sunroof)) 

The roof is fully closed by PRE-SAFE, if it was open in the lifting direction before the PRE-SAFE measure occurred. If the roof was opened in the sliding direction before the PRE-SAFE measure occurred, it is closed apart from a residual gap. This ensures that no objects can penetrate into the vehicle interior and no body parts (e.g. arms) of the occupants can protrude from the vehicle in the event of a potential accident. This also allows the smoke particles generated by the pyrotechnical restraint equipment to disperse quickly.

The Electronic Stability Program control unit sends information about the PRE-SAFE status and the request for PRE-SAFE adjustment over the chassis FlexRay, electronic ignition lock control unit and interior CAN to the panoramic sliding sunroof control unit in the panoramic sliding sunroof control module. Any automatic movement or manual setting that is active is aborted. The automatic reversing function is active when the roof is being closed. If required, the closing process is reversed.

The PRE-SAFE setting continues until

• The roof reaches the PRE-SAFE position
• The impact occurs

Closing of the roof can be aborted at any time by means of manual settings. Following the PRE-SAFE situation, the roof must be manually moved back into the desired position.

Detailed information on how to control the roof can be found in a separate function description.

Function sequence for display of fault messages 

If the reversible belt tensioner or active seat belt buckle control unit (with code 305 (Rear PRE-SAFE)) detects faults, appropriate messages are displayed in the instrument cluster. Faults of other components that are part of PRE-SAFE are not displayed as PRE-SAFE faults.

The reversible emergency tensioning retractors send the request to display a fault message over the user interface CAN to the instrument cluster. The active seat belt buckle control unit (with code 305 (Rear PRE-SAFE)) transmits the request to display a fault message to the instrument cluster via the interior CAN, electronic ignition lock control unit and user interface CAN.

Adjustment of the front passenger seat and rear seat (with code 223 (Electrically adjustable rear bench seat)) is canceled if the PRE-SAFE position has not yet been reached. The closing of side windows or the roof (with code 413 (Panoramic sliding sunroof)) is not canceled. The automatic closing function continues until the PRE-SAFE position has been reached. The front reversible belt tensioner is released and the rear left or rear right active seat belt buckle (with code 305 (Rear PRE-SAFE)) is moved back to its default position.

The reversible emergency tensioning retractors are equipped with a mechanical acceleration sensor, which locks the belt extension in the event of any vehicle acceleration of a > 0.3 g. For this reason, the belt may remain mechanically locked even when the reversible emergency tensioning retraction has been completed. In the event of an impact that is detected by the supplemental restraint system control unit, all adjustments are immediately stopped.

	Electrical function schematic, pre-safe	Model 217, 222 as of model year 2018	PE91.40-P-2051-97SEB
		Model 217, 222 up to model year 2018	PE91.40-P-2051-97SEA
	Overview of system components for PRE-SAFE (R)		GF91.40-P-9997LF