PRE-SAFE function - GF91.40-P-0001CW
MODEL 204.0/2 with CODE (299) PRE-SAFE up to Model Year 08
General information
PRE-SAFE is activated in the event of critical drive situations, in other words in a potential accident situation. The goal is to create the most favorable conditions possible for the occupants during the expected accident by activating the functions before the actual impact.
The data of the Electronic Stability Program control unit (N30/4) are evaluated to trigger the PRE-SAFE functions.
Function requirements
- Circuit 15 ON
- Vehicle speed v > 30 km/h
- Circuit 61 ON
Possible triggering criteria
- PRE-SAFE longitudinal dynamics
- PRE-SAFE lateral dynamics
PRE-SAFE comprises the following functions
- Reversible emergency tensioning retraction for driver and front passenger
- Front passenger seat adjustment (with code (242) Electrically adjustable front passenger seat with memory)
- Automatic closing of all door's windows
- Automatic closing of the tilting/sliding roof (SHD) (with code (414) Power glass tilting/sliding sunroof)
- Automatic closing of the panoramic sliding sunroof (with code (413) Panoramic glass sunroof with top sliding sunroof)
PRE-SAFE longitudinal dynamics
- Emergency stop:
- The driver hits the brake pedal hard
(z . B. startle response)
- Secondary brake application as a result of a panic reaction:
- The vehicle does not decelerate according to the driver's intention due to special weather conditions (ice, snow or aquaplaning). The driver depresses the brake pedal down to the maximum pedal travel
PRE-SAFE lateral dynamics
- Excessive oversteer:
- A major rear axle slip angle occurs, which cannot even be stabilized by the Electronic Stability Program (ESP)
- Excessive understeer:
- A major front axle slip angle occurs for an extended period, which cannot even be stabilized by the ESP
- Critical steering movement:
- Steering movement of the driver, which is probably due to a startle reaction and can lead to instability of the vehicle. Activation does not start until after speeds of v > 140 km/h have been reached. The activation characteristics become more sensible with increasing speeds
The following table illustrates, which functions are activated in the event of longitudinal dynamics or lateral dynamics.
| Activated PRE-SAFE function | PRE-SAFE longitudinal dynamics | PRE-SAFE lateral dynamics |
|---|---|---|
| Reversible emergency tensioning retraction | X | X |
| Adjustment of front passenger seat | X | X |
| Closing of windows | X | |
| Closing of tilting/sliding roof | X | |
| Closing of top sliding roof | X |
The sequence of PRE-SAFE activities is coordinated by the Electronic Stability Program control unit, which is connected to the interior CAN via chassis CAN and via the front SAM control unit with fuse and relay module (N10/1). The existing vehicle systems are used to realize the PRE-SAFE function.
Reversible emergency tensioning retraction for driver and front passenger
The left front reversible emergency tensioning retractor (A76) and the right front reversible emergency tensioning retractor (A76/1) reduce the existing seat belt slack in dangerous situations. Thus, the occupants are secured in position in the seats at an early point in time in order to prevent displacement.
As a result, the occupants are retained in a favorable seat position in the event of an accident, in which the conventional restraint systems can have their optimum protective effect.
Function requirements
- PRE-SAFE has been activated
- Front seat belt inserted in seat belt buckle
Function sequence of reversible emergency tensioning retraction for the driver and front passenger
The reversible emergency tensioning retractors receive the signal for emergency tensioning retraction from the Electronic Stability Program control unit via the chassis CAN.
The reaction of the reversible emergency tensioning retractors varies depending on the recognized PRE-SAFE situation:
- in the event of a longitudinal dynamics situation, the belt is tensioned as fast as possible (within approx. t = 120 ms) to a defined power level
- in the event of a lateral dynamics situation, the tensioning time is parameterizable
At the end of the tensioning request, the belt is released again.
The reversible emergency tensioning retractors are activated only, if the vehicle speed exceeds > 30 km/h and the latches of the seat belts are inserted into the seat belt buckles. This is recognized via the seat belt buckle switch on the left front seat (S68/1) and the seat belt buckle switch on the right front seat (S68/2) by the supplemental restraint system control unit (N2/10). The supplemental restraint system control unit transmits the status of the seat belt buckles to the Electronic Stability Program control unit via chassis CAN.
If the speed drops below 30 km/h during a PRE-SAFE situation, all PRE-SAFE functions remain active until the speed has dropped below 3 km/h.
Adjustment of front passenger seat
Positioning of the front passenger seat is used to move the front passenger into a favorable position in the event of an imminent impact. In this position, the restraint systems can provide the best protective effect possible.
The PRE-SAFE function of the front passenger seat can be switched off via STAR DIAGNOSIS.
Function requirements
- PRE-SAFE has been activated
- Front passenger seat set to an unfavorable position (e.g. reclining position)
- Normalized front passenger seat adjustment
Function sequence of front passenger seat adjustment
The adjustment of the front passenger seat is controlled by the front passenger seat control unit (N32/2).
Depending on the current setting, the following adjustments can be made:
- Seat fore/aft position
- using the front passenger seat fore/aft adjustment motor (M28/1)
- Seat height
- using the front passenger seat height adjustment motor (M28/2)
- Seat inclination
- using the front passenger seat inclination adjustment motor (M28/3)
- Backrest inclination
- using the front passenger seat backrest inclination adjustment motor (M28/5)
The automatic adjustment of the front passenger seat can be interrupted at any time by operating the right front seat adjustment switch group (S23).
If a PRE-SAFE situation continues to be present, the front passenger seat is adjusted again via PRE-SAFE after the manual adjustment has been completed.
The adjustment time takes until:
- the target area has been reached (seat in optimum position)
- the occurrence of the impact
- the PRE-SAFE situation ends
The front passenger seat does not automatically return into the position before the PRE-SAFE situation, but has to be adjusted via the right front seat adjustment switch group if necessary.
Seat adjustment if the occupants are not buckled up:
The system moves the seat into a position that is suitable for situations that are unfavorable with regard to safety technology.
The status of the right front seat belt buckle switch seat is transmitted by the supplemental restraint system control unit via chassis CAN to the front SAM control unit, and from there via the interior CAN to the front passenger seat control unit.
Automatic closing of the tilting/sliding roof or the panoramic sliding sunroof
The purpose of closing the existing roof via PRE-SAFE is to prevent that, if an accident occurs, objects enter the vehicle interior or that body parts (e.g. arms) of the occupants can reach out of the vehicle.
Function requirements
- PRE-SAFE has been activated
- Normalized tilting/sliding roof or panoramic sliding sunroof
Automatic closing function sequence of the tilting/sliding roof or the panoramic sliding sunroof
The overhead control panel control unit (N70) (with code (414) Power glass tilting/sliding sunroof) or the panoramic sliding roof control module (A98) (with code (413) Panoramic glass sunroof with top sliding sunroof) receives the request of the Electronic Stability Program control unit via interior CAN from the front SAM control unit and triggers the closing of the roof.
The roof is closed leaving a gap of approx. 50 mm in order to ensure that, in the event of the possible subsequent impact, the smoke that builds up as a result of the pyrotechnical restraint systems can be exhausted. Closing can be aborted anytime by manually operating the tilting/sliding roof switch (N70s1) (with code (414) Power glass tilting/sliding sunroof) or the panoramic sliding roof switch (N70/3s1) (with code (413) Panoramic glass sunroof with top sliding sunroof).
The anti-pinch protection is active while the roof is closed. If required, the closing process is reversed.
If closing is activated via PRE-SAFE during a manual adjustment, the manual adjustment request is completed first and then closing via PRE-SAFE.
If closing is activated via PRE-SAFE during an automatic process, the automatic process is aborted and closing is carried out via PRE-SAFE.
The roof has to be manually moved back into the desired position after the PRE-SAFE situation has ended.
The PRE-SAFE function of the roof can be switched off via STAR DIAGNOSIS.
Automatic closing of the windows
The purpose of closing the windows via PRE-SAFE is to prevent that, if an accident occurs, objects enter the vehicle interior or that body parts (e.g. arms) of the occupants can reach out of the vehicle.
Function requirement
- PRE-SAFE has been activated
- Power window normalized
Function sequence of automatic closing of the windows
The following control units:
- Left front door control unit (N69/1)
- Right front door control unit (N69/2)
- Left rear door control unit (N69/3)
- Right rear door control unit (N69/4)
receive the signal for closing the windows via interior CAN from the front SAM control unit.
The windows are closed leaving a gap of approx. 50 mm in order to ensure that, in the event of the possible subsequent impact, the smoke that builds up as a result of the pyrotechnical restraint systems can be exhausted.
When the windows are closed via PRE-SAFE, the anti-pinch protection is active. If required, the closing process is reversed. Closing can be aborted at any time by a manual request via the:
- Driver-side power window and outside mirror adjustment switch group (S20) or the
- passenger-side power window switch (S21/2) or the
- left rear power window switch (S21/3) or the
- right rear power window switch (S21/4)
for the particular window.
If closing is activated via PRE-SAFE during an automatic lowering process, the automatic lowering process is aborted and closing is carried out via PRE-SAFE.
The windows have to be manually moved back into the desired position after the PRE-SAFE situation has ended.
Function when the ESP is switched off
The triggering threshold for the PRE-SAFE functions is increased, if the ESP has been shut off manually via the ESP button (S6/1s5) in the instrument panel switch group (S6/1). Signals of the instrument panel switch group are read in by the front SAM control unit via instrument panel LIN. The front SAM control unit transmits the signals to the Electronic Stability Program control unit via chassis CAN.
Error messages
If a fault is recognized in a reversible emergency tensioning retractor, then it is displayed on the multifunction display (A1p13) in the instrument cluster (A1). Faults of other components that are part of PRE-SAFE are not displayed as PRE-SAFE faults.
Ending the PRE-SAFE functions
PRE-SAFE is deactivated as soon as a PRE-SAFE longitudinal dynamics situation or lateral dynamics situation is no longer present. The Electronic Stability Program control unit transmits a signal for shutting off the PRE-SAFE functions via the chassis CAN.
The signal is transmitted to the involved control units via the front SAM control unit via the interior CAN.
The adjustment of the front passenger seat is aborted, if the PRE-SAFE position has not yet been reached.
The closing function of the 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.
The reversible emergency tensioning retractors are equipped with a mechanical acceleration sensor, which locks the seat belt extension at a vehicle acceleration of a > 0.3 g.
Therefore, the seat belt can remain mechanically locked even though the reversible emergency tensioning retraction has ended.
In the event of an impact that is recognized by the supplemental restraint system control unit, all adjustments are stopped immediately.
| Pre-Safe electrical function diagram | PE91.40-P-2051-99FAA | ||
| PRE-SAFE, location of components | GF91.40-P-0001-01CW | ||
| PRE-SAFE, block diagram | GF91.40-P-0001-03CW | ||
| Front reversible emergency tensioning retractor, component description | A76, A76/1 | GF91.40-P-4020CW | |
| Panoramic sliding roof control module, component description | A98 With code (413) Panoramic glass sunroof with top sliding sunroof |
GF77.20-P-4106CW | |
| Power window motor, component description | M10/3, M10/4, M10/5 and M10/6 | GF72.29-P-6030CW | |
| Seat adjustment motor, component description | M27/1, M27/2, M27/3, M27/4, M27/5, M28/1, M28/2, M28/3, M28/4 and M28/5 | GF91.29-P-5213CW | |
| Supplemental restraint system control unit, component description | N2/10 | GF91.60-P-4068CW | |
| Front SAM control unit with fuse and relay module, component description | N10/1 | GF54.21-P-6070CW | |
| Electronic Stability Program control unit, component description | N30/4 | GF42.45-P-5119CW | |
| Front passenger seat control unit, component description | N32/2 With code (242) Electrically adjustable front passenger seat with memory |
GF91.29-P-5241CW | |
| Left front door control unit, component description | N69/1 | GF72.29-P-6001CW | |
| Right front door control unit, component description | N69/2 | GF72.29-P-6009CW | |
| Rear door control unit, component description | N69/3, N69/4 | GF72.29-P-6021CW | |
| Overhead control panel control unit, component description | N70 With code (414) Power glass tilting/sliding sunroof |
GF82.20-P-5216CW | |
| ESP button, component description | S6/1s5 | GF42.45-P-5122CW | |
| Driver-side power window and outside mirror adjustment switch group, component description | S20 | GF54.25-P-4250CW | |
| Seat adjustment switch group, component description | S22, S23 With code (275) Memory package (driver seat, steering column, mirrors) or with code (242) Electrically adjustable front passenger seat with memory |
GF91.29-P-5206CW | |
| Seat belt buckle switch, component description | S68/1, S68/2 | GF91.60-P-4045CW |