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

MODEL 207.3/4 

Fig 1: Pre-Safe Block Diagram
G10082027Courtesy of MERCEDES-BENZ USA

Up to 31.5.13 

Fig 2: Pre-Safe Block Diagram
G10082028Courtesy of MERCEDES-BENZ USA

As of 1.6.13 

Function requirements, general 

IMPORTANT The status of circuit 15 is sent by the electronic ignition lock control unit via chassis CAN (up to 31.5.13) or via chassis CAN 1 (as of 1.6.13) to the Electronic Stability Program control unit.

The "Engine running" or "Drivetrain operational" signal is sent by the CDI control unit (with diesel engine) or the ME-SFI [ME] control unit (with gasoline engine) via chassis CAN (up to 31.5.13) or via chassis CAN 1 (as of 1.6.13) 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. To do so, PRE-SAFE constantly evaluates the sensor data of systems such as the Electronic Stability Program (ESP®) and the Brake Assist System PLUS (BAS PLUS) (up to 31.5.13 with code (233) DISTRONIC PLUS or as of 1.6.13 with code (268) Brake Assist System PLUS or code (269) Brake Assist System PLUS crosstraffic (BAS+Q)) and can thus 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 controlled on vehicles up to 31.5.13 by the Electronic Stability Program control unit (without code (233) DISTRONIC PLUS) or by the Premium Electronic Stability Program control unit (with code (233) DISTRONIC PLUS). As of 1.6.13, control is performed by the 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: Vehicles up to 31.5.13:

Vehicles as of 1.6.13:

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® was manually switched to passive via the ESP button in the instrument panel switch group. The front SAM control unit reads in the status of the ESP button via instrument panel LIN and sends this via chassis CAN (up to 31.5.13) or chassis CAN 1 (as of 1.6.13) to the Electronic Stability Program control unit.

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 31.5.13) or chassis CAN 1 (as of 1.6.13) 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. 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 sends information about the PRE-SAFE status and the PRE-SAFE stage via chassis CAN (up to 31.5.13) or chassis CAN 1 (as of 1.6.13) to the reversible emergency tensioning retractors. The supplemental restraint system control unit sends the crash signal via chassis CAN (up to 31.5.13) or chassis CAN 1 (as of 1.6.13) to the reversible emergency tensioning retractors. In order to tension the seat belt, the respective reversible emergency tensioning retractor directly actuates the integrated front reversible emergency tensioning retractor actuator motor.

Additional function requirements for seat belt adjustment 

IMPORTANT The instrument cluster sends the status of the seat belt adjustment function on vehicles up to 31.5.13 via chassis CAN and on vehicles as of 1.6.13 via chassis CAN 2, front SAM control unit and chassis CAN 1 to the reversible emergency tensioning retractors.

Function sequence for seat belt adaptation 

The seat belt adjustment function reduces the existing seat belt slack by tensioning the seat belts 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 of the seat belt 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 31.5.13) or chassis CAN 1 (as of 1.6.13) to the reversible emergency tensioning retractors. In order to tension the seat belt, the respective reversible emergency tensioning retractor directly actuates the integrated front reversible emergency tensioning retractor actuator motor. This tightens the belt strap at a constant speed until the seat belt slack has been reduced.

Additional function requirements for positioning front passenger seat (with code (242) Electrically adjustable front passenger seat with memory) 

IMPORTANT The supplemental restraint system control unit sends the status of the front passenger seat occupied recognition via chassis CAN (up to 31.5.13) or chassis CAN 1 (as of 1.6.13), front SAM control unit and interior CAN to the front passenger seat control unit.

Function sequence for positioning of front passenger seat (with code (242) Electrically adjustable front passenger seat with memory) 

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 31.5.13) or chassis CAN 1 (as of 1.6.13), 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 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 belt buckle restraint system switch directly and sends this via chassis CAN (up to 31.5.13) or chassis CAN 1 (as of 1.6.13), front SAM control unit and interior CAN to the front passenger seat control unit.

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

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 31.5.13) or chassis CAN 1 (as of 1.6.13), front SAM control unit and interior CAN to the following control units:

Any automatic opening or manual setting that is active is aborted. When the side windows are closed via PRE-SAFE, the obstruction sensor is active. If required, the closing process is reversed. The PRE-SAFE setting continues until:

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.

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

Additional function requirements for closing panoramic sliding roof (with code (413) Panoramic glass sunroof with top sliding sunroof) 

Function sequence for closing panoramic sliding roof (with code (413) Panoramic glass sunroof with top 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 via chassis CAN (up to 31.5.13) or chassis CAN 1 (as of 1.6.13), front SAM control unit and interior CAN to the panoramic sliding sunroof control unit in the panoramic sliding sunroof control module.

If closing is activated by PRE-SAFE during a manual adjustment, the manual adjustment request is completed first and then closing by PRE-SAFE. If closing is activated by PRE-SAFE during an automatic process, the automatic process is aborted and closing is carried out by PRE-SAFE. The anti-pinch protection is active when the roof is being closed by PRE-SAFE. If required, the closing process is reversed.

The PRE-SAFE setting continues until:

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

IMPORTANT Detailed information on controlling the roof is available in the separate function descriptions "Electric panoramic sliding window, function".

Function sequence for display of fault messages 

If the reversible emergency tensioning retractors detect faults, appropriate 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 to display the fault message on vehicles up to 31.5.13 via chassis CAN and on vehicles as of 1.6.13 via chassis CAN 1, 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 current situation is deemed to be no longer critical. To do this, the Electronic Stability Program control unit takes back the information about the PRE-SAFE status from chassis CAN (up to 31.5.13) or chassis CAN 1 (as of 1.6.13).

The adjustment of the front passenger seat is aborted. Closing of the side windows and the 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. When there is a crash event that is detected by the supplemental restraint system control unit, all adjustments are immediately stopped.

  Electrical function schematic, pre-safe MODEL 207.3/4 up to model year 2014 PE91.40-P-2051-97EAA 
    MODEL 207.3/4 as of model year 2014 PE91.40-P-2051-97EAB
  Overview of PRE-SAFE system components   GF91.40-P-9997CA 
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