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PRE-SAFE function - GF91.40-P-0001FL

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MODEL 212 

Up to 28.2.13 

Fig 1: Pre-Safe Function Block Diagram - Model 212 Up To 28.2.13
G10050634Courtesy of MERCEDES-BENZ USA

As of 1.3.13 

Fig 2: Pre-Safe Function Block Diagram - Model 212 As Of 1.3.13
G10050635Courtesy of MERCEDES-BENZ USA

Function requirements, general 

IMPORTANT The electronic ignition lock control unit sends the status of circuit 15 via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13) to the front SAM control unit and the Electronic Stability Program control unit or the regenerative braking system control unit or the Premium Electronic Stability Program control unit.

The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal or the "Drivetrain operational" signal via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13) to the Electronic Stability Program control unit or the regenerative braking system control unit or the Premium Electronic Stability Program control unit.

PRE-SAFE, general 

The PRE-SAFE function is activated in critical situations, i.e. in a potential accident situation. The functions that are activated before the potential accident (preventive measures) should create the optimum prerequisites for the occupants for minimizing the consequences of the anticipated accident.

The PRE-SAFE function is controlled by the:

The aforementioned control units are referred to in the following as "Electronic Stability Program control unit".

The PRE-SAFE function includes the following subfunctions:

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.

IMPORTANT Detailed information about acquisition of these variables can be found in the separate function description "Adaptive Brake (ABR) function".

The Electronic Stability Program control unit also evaluates the following signals from different driving assistance systems, depending on the equipment variant:

Vehicles up to 28.2.13:

Vehicles as of 1.3.13:

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

The triggering threshold for the PRE-SAFE functions is increased if the ESP® has been switched to passive.

Additional function requirements, reversible emergency tensioning retraction 

IMPORTANT The supplemental restraint system control unit reads in the status of the respective belt buckle restraint system switch directly and sends this via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13) to the reversible emergency tensioning retractors.

Function sequence for 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. At the end of 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 sends information about the PRE-SAFE status and the PRE-SAFE stage via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13) to the reversible emergency tensioning retractors. The supplemental restraint system control unit sends the crash signal via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13) to the reversible emergency tensioning retractors. In order to tension the seat belt, the respective reversible emergency tensioning retractor actuates the integrated front reversible emergency tensioning retractor actuator motor directly.

Additional function requirements for seat belt adaptation 

IMPORTANT The instrument cluster sends the status of the seat belt adaptation function on vehicles up to 28.2.13 via chassis CAN and on vehicles as of 1.3.13 via chassis CAN 2, the front SAM control unit and chassis CAN 1 to the reversible emergency tensioning retractors.

Function sequence for seat belt adaptation 

The seat belt adaptation function reduces the amount of seat belt slack by tensioning the seat belts of the driver and front passenger seats using an electric motor. The function is triggered when the belt latch is inserted into the respective seat belt buckle. The insertion of the belt latch into the belt buckle is recorded via the status of the respective belt buckle restraint system switch.

The supplemental restraint system control unit reads in the status of the respective belt buckle restraint system switch directly and sends this via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13) to the reversible emergency tensioning retractors. In order to tension the seat belt, the respective reversible emergency tensioning retractor actuates the integrated front reversible emergency tensioning retractor actuator motor directly. This tightens the belt strap at a constant speed until the seat belt slack has been reduced.

Additional function requirements for front passenger seat positioning (with code (275) Memory package for electrically adjustable front seats) 

IMPORTANT Detailed information about seat occupancy recognition can be found in the separate function description "Supplemental restraint system, function".

Function sequence for front passenger seat positioning (with code (275) Memory package for electrically adjustable front seats) 

In order to optimize the protective effect of the conventional restraint equipment, the front passenger seat in 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 via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13), the front SAM 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:

The PRE-SAFE setting continues until:

IMPORTANT Detailed information about adjusting the front passenger seat can be found in the separate function description "Electrical seats, function" in the subfunction "Electrical seat adjustment (ESE), function".

IMPORTANT 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.

IMPORTANT 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 unit reads in the status of the respective belt buckle restraint system switch directly and sends this via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13), the front SAM control unit and interior CAN to the front passenger seat control unit.

Additional function requirement for adjusting the seat contour (with code (432) Active multicontour seat) 

IMPORTANT The supplemental restraint system control unit reads in the status of the respective belt buckle restraint system switch directly and sends this via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13), the front SAM control unit and interior CAN to the left front dynamic multicontour seat control unit and the right front dynamic multicontour seat control unit.

Function sequence for adjusting the seat contour (with code (432) Left and right dynamic multicontour seat) 

In order to optimize the protective effect of the conventional restraint equipment, the seat contour of the driver and front passenger seat is adjusted before a potential accident. The Electronic Stability Program control unit sends information about the PRE-SAFE status and the request for PRE-SAFE adjustment via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13), the front SAM control unit and interior CAN to the dynamic multicontour seat control units. Any memory or manual setting that may be active is aborted.

The following settings are made:

The PRE-SAFE setting continues until:

IMPORTANT Detailed information about adjusting the seat contour can be found in the separate function description "Electric seats, function" in the subfunction "Dynamic multicontour seat, function".

IMPORTANT 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 the air cushions in the lumbar area is returned to the respective initial status.

Additional function requirements for closing the side windows 

Function sequence for closing the 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 via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13), the front SAM control unit and interior CAN to the following control units:

Then the side windows are closed until only a gap is left.

The PRE-SAFE setting continues until:

IMPORTANT Detailed information about controlling the side windows can be found in the separate function description "Power windows (EFH), function".

IMPORTANT The closing of the respective side window by PRE-SAFE can be interrupted at any time by manual adjustment requests. The side windows have to be manually moved back into the desired position after the PRE-SAFE situation has ended.

Additional function requirements for automatic closing of the tilting/sliding roof (SHD) (with code (414) Power glass tilting/sliding sunroof) or the panoramic sliding sunroof (with code (413) Panoramic glass sunroof with top sliding sunroof) 

Function sequence for automatic closing of the tilting/sliding roof (SHD) (with code (414) Power glass tilting/sliding sunroof) or the panoramic sliding sunroof (with code (413) Panoramic glass sunroof with top sliding sunroof) 

The sliding roof is fully closed if it was open in the lifting direction before the PRE-SAFE measure occurred. If the sliding 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 via chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13), the front SAM control unit and interior CAN to the panoramic sliding sunroof control unit in the panoramic sliding sunroof control module or the overhead control panel control unit. Then the sliding roof is closed apart from a small gap.

The PRE-SAFE setting continues until:

IMPORTANT Detailed information about controlling the sliding roof can be found in the separate function description "Power tilting/sliding roof (SHD), function" or "Electric panoramic sliding roof, function".

IMPORTANT The anti-pinch protection is active when the sliding roof is being closed. If required, the closing process is reversed. The closing of the sliding roof can be aborted at any time by means of manual intervention. The sliding roof must be manually moved back into the desired position after the PRE-SAFE situation.

Function sequence for display of fault messages 

If the reversible emergency tensioning retractors detect faults, corresponding messages are displayed in the multifunction display of 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 for displaying the fault message on vehicles up to 28.2.13 via chassis CAN and on vehicles as of 1.3.13 via chassis CAN 1, the front SAM control unit and chassis CAN 2 to the instrument cluster.

Function sequence for terminating PRE-SAFE functions 

The PRE-SAFE function is deactivated as soon as the prevailing situation is deemed to be no longer critical. For this purpose, the Electronic Stability Program control unit takes the information concerning the PRE-SAFE status from chassis CAN (up to 28.2.13) or chassis CAN 1 (as of 1.3.13).

Positioning of the front passenger seat and adjustment of the seat contour of the driver or front passenger seat are aborted. Closing of the side windows and the sliding roof is not aborted. The automatic closing function continues until the PRE-SAFE position has been reached. The reversible emergency tensioning retraction is released as soon as the vehicle acceleration has dropped below a value of a = 0.3 g.

IMPORTANT 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. All adjustments stop immediately if the supplemental restraint system control unit detects an accident.

  Electrical function schematic, pre-safe MODEL 212 up to model year 2014 PE91.40-P-2051-97DAA
MODEL 212 as of model year 2014 PE91.40-P-2051-97DAB
  Overview of PRE-SAFE system components   GF91.40-P-9997FL 
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