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

MODEL 216.3, 221.0 /1 as of model year 2009 

/YoM 08 

Function requirements, general 

IMPORTANT The status of circuit 15 is sent by the EZS control unit (N73) to the interior CAN (CAN B).

The "Engine running" status is made available by the CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine) via chassis CAN (CAN E).

PRE-SAFE, general 

The PRE-SAFE system is activated in critical driving states, i.e. 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 ESP control unit (N47-5) (without model 221.095/195) or the regenerative braking system control unit (N30/6) (model 221.095/195) is evaluated for triggering the PRE-SAFE functions.

The PRE-SAFE function consists of the following subfunctions:

Additional function requirements for seat belt slack reduction (in the case of model 221) 

Function sequence for seat belt slack reduction (on model 221) 

The seat belt slack reduction function reduces the existing seat belt slack once the seat belt is fastened.

The insertion of the seat belt tab into the belt buckle triggers the seat belt slack reduction function. This is recognized via the driver seat belt buckle and seat belt reminder warning switch (S68/1) and the front passenger seat belt buckle and seat belt reminder warning switch (S68/2) by the restraint systems control unit (N2/7).

The left front reversible emergency tensioning retractor (A76) and right front reversible emergency tensioning retractor (A76/1) now tension the belt strap at a speed of v = 50 mm/s (±10 %) until the seat belt slack is reduced. The belt force generated here increases at the end of the pretensioning process to F = 20 N (±20 %). Once the belt force has been reached, the seat belt is pretensioned for another t = 400 ms. Following expiration of this time, the seat belt slack reduction function is ended.

Function sequence for registering of activation criteria 

The recording of the activation criteria function comprises the following subfunctions:

Function sequence for registering the PRE-SAFE longitudinal dynamics 

IMPORTANT The radar sensors control unit (SGR) (N62/1) (with code (233) DISTRONIC PLUS up to 31.8.10) or video and radar sensor system control unit (N62/2) (with code (233) DISTRONIC PLUS as of 1.9.10) initiates braking of the vehicle (PRE-SAFE brake) because of information from the DTR controller unit (A89).

On vehicles with code (238) Active Lane Keeping Assist, the video and radar sensor system control unit initiates a corrective brake intervention if necessary if a collision hazard is detected during lane change.

IMPORTANT Detailed information on this can be found in the function description "DISTRONIC PLUS" or the function description "Active Lane Keeping Assist".

Function sequence for determining the PRE-SAFE lateral dynamics 

Driver steering movement which is probably due to a startled reaction and which may lead to instability of the vehicle.

Activation does not take place until speeds of v > 140 km/h have been reached. The activation characteristics become more sensitive with increasing speeds

Function sequence for recording the vehicle surroundings (with code (233) DISTRONIC PLUS) 

In order to prevent a possible collision with vehicles or obstacles, radar sensors are installed in the front bumper.

Driving situations in which danger of possible collisions may occur:

An unexpected obstacle appears while in the curve

The vehicle distance from a recognized object (vehicle, obstacle) is determined by the inner left radar sensor, front bumper (A86/1b2) and the inner right radar sensor, front bumper (A86/1b3) at current closing speed.

The radar sensors (short range sensors) recognize obstacles within a short range up to s = 30 m and at an angle up to 140°.

Obstacles can hereby be detected early and reversible occupant protection measures (e.g. occupant immobilization) can be initiated. The data for determining the severity of the collision and the time of the collision are read in by the radar sensors control unit or video and radar sensor system control unit and provided to the restraint systems control unit.

Accordingly, the restraint systems control unit can then trigger the corresponding restraint equipment earlier.

The sequence of PRE-SAFE functions is coordinated by the PRE-SAFE master. This is integrated into the ESP control unit or into the regenerative braking system control unit. If the PRE-SAFE master recognizes a critical driving situation, is activates the following actuators:

IMPORTANT The signals of the short range front radar sensors are sent via sensor CAN (CAN S) to the radar sensors control unit or the video and radar sensor system control unit and evaluated.

Function sequence when the ESP is switched off 

The triggering threshold for the PRE-SAFE functions is raised if the ESP was shut off manually via the ESP OFF switch (S6/2s11) (model 211 up to 31.05.09) in the cockpit switch group (S6/2). The signals from the cockpit switch group are read in by the upper control panel control unit (N72/1) via instrument panel LIN (LIN 1). The upper control panel control unit transmits the signals via the interior CAN to the central gateway control unit (N93). The central gateway control unit sends the signals via chassis CAN to the ESP control unit or to the regenerative braking system control unit.

IMPORTANT The ESP OFF switch is discontinued on model 221 as of 31.5.09. The ESP can be switched off via the left multifunction steering wheel button group (S110) on model 221 as of 1.6.09. The message is shown in the multifunction display (A1p13) of the instrument cluster.

Function sequence for reversible emergency tensioning retraction for driver and front passenger (with model 221) 

The left front reversible emergency tensioning retractor and the right front reversible emergency tensioning retractor 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.

The occupants are therefore held in a favorable seat position in the event of an accident, allowing the conventional restraint systems to have their optimum protective effect.

The reversible emergency tensioning retractors receive the signal for emergency tensioning retraction via chassis CAN from the ESP control unit or the regenerative braking system control unit.

The reaction of the reversible emergency tensioning retractors varies depending on the recognized PRE-SAFE situation:

At the end of the tensioning request, the belt is released again. The reversible emergency tensioning retractors are activated only if the vehicle speed is v > 30 km/h and the latches of the seat belts are inserted into the seat belt buckles.

This is recognized via the driver seat belt buckle and seat belt reminder warning switch and the front passenger seat belt buckle and seat belt reminder warning switch by the restraint systems control unit.

The restraint systems control unit sends the status of the seat belt buckles via chassis CAN to the ESP control unit or to the regenerative braking system control unit.

If the speed drops below v = 30 km/h during a PRE-SAFE situation, all PRE-SAFE functions remain active until the speed has dropped below

v = 3 km/h.

Additional function requirements for adjusting the front passenger seat 

The status of the front passenger seat belt buckle and seat belt reminder warning switch is transmitted by the restraint systems control unit via the chassis CAN to the central gateway control unit. This routes the status via the interior CAN to the right front seat control unit (N32/2).

Depending on the current setting, the following adjustments can be made by the right front seat control unit:

Function sequence for adjusting front passenger seat 

Adjustment of the front passenger seat is used to move the front passenger into a favorable position in the event of an imminent impact.

The front passenger seat is adjusted according to whether the front passenger is strapped in or not strapped in.

The automatic adjustment of the front passenger seat can be interrupted at any time by operating the right front seat operation 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 process lasts until:

The front passenger seat does not automatically return to the position before the PRE-SAFE situation, but rather has to be adjusted via the right front seat operation switch group as necessary.

Additional function requirements for adjustment of individual rear seats 

(on model 221 with code (223) Rear bench seat with electrically adjustable outer seats with PRE-SAFE positioning function for outer seats and outer head restraints) 

Function sequence for adjustment of individual rear seats (on model 221 with code (223) Rear bench seat with electrically adjustable outer seats with PRE-SAFE positioning function for outer seats and outer head restraints) 

Rear seat adjustment is used to move the rear occupants into a favorable position in the event of an imminent impact.

In this position, the restraint equipment can provide the best protective effect possible. The adjustment occurs according to whether the rear occupants are strapped in or not strapped in.

The status of the left rear seat belt buckle switch (S68/11) and the right rear seat belt buckle switch (S68/12) is forwarded by the rear SAM control unit with fuse and relay module (N10/2) via the interior CAN to the central gateway control unit, and from there via the interior CAN to the rear seat control unit (N25/6).

Depending on the current setting, the following adjustments can be made by the rear seat control unit:

Seat adjustment if occupants are buckled up

Dependent upon how the rear seats are set, the:

Seat adjustment if 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 adjustment process lasts until:

IMPORTANT The PRE-SAFE function of the rear seats can be switched off using the diagnostic tester.

Function sequence for closing all door windows 

The following control units receive the signal for the ESP control unit or the regenerative braking system control unit to close the windows from the central gateway control unit via interior CAN:

The windows are closed by the left front power window motor (M10/3), right front power window motor (M10/4), left rear power window motor (M10/5) and the right rear power window motor (M10/6) to a gap of s = 50 mm, to ensure that in the event of any subsequent impact the smoke particles generated by the pyrotechnical restraint equipment are then extracted.

The anti-pinch protection is active when the windows are closed via PRE-SAFE. If required, the closing process is reversed.

The closing process can be stopped at any time by a manual request from the following controls for the respective window:

Function sequence for automatic closing of tilting/sliding roof (on model 221 with code (414) Power glass tilting/sliding roof or on model 216) 

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.

Once the PRE-SAFE situation has ended, the windows must be manually moved back into the desired position.

Closing the tilting/sliding roof via PRE-SAFE is intended to prevent objects from penetrating the vehicle interior and stop the occupants' body parts (such as arms) from protruding from the vehicle if an accident occurs.

The overhead control panel control unit (N70) receives the request of the ESP control unit or the regenerative braking system control unit from the central gateway control unit via interior CAN and triggers the closure of the tilting/sliding roof.

The tilting/sliding roof is closed leaving a gap of s = 50 mm in order to ensure that, in the event of a possible subsequent impact, smoke particles generated by the pyrotechnical restraint systems can escape.

Closing can be aborted at any time by manually operating the roof switch (N70s1).

The anti-pinch protection is active when the tilting/sliding roof is being 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.

Once the PRE-SAFE situation has ended, the tilting/sliding roof must be manually moved back into the desired position.

IMPORTANT The PRE-SAFE function of the tilting/sliding roof can be switched off using the diagnostic tester.

Function sequence for adjustment of the seat contour 

(with code (409) Left/right front multicontour seats or with code (432) Left and right dynamic multicontour seat or on model 221 with code (406) Rear multicontour seats) 

The purpose of inflating the side inserts in the seats is to centrally secure the occupants in position in the seats. In this position, the restraint equipment can provide the best protective effect possible. The following control units receive the signal of the ESP control unit or the regenerative braking system control unit to close the windows from the central gateway control unit via interior CAN:

With code (409) Left/right front multicontour seats:

With code (432) Left and right dynamic multicontour seat:

For model 221 with code (406) Rear multicontour seats:

The seat contour is adjusted until the PRE-SAFE specified pressure is reached or until the end of the PRE-SAFE situation. Once the PRE-SAFE situation has ended, the filling status of the side inserts is returned to the respective initial status it had before PRE-SAFE was activated.

IMPORTANT The adjustment of the seat contour can be aborted at any time via a manual adjustment or by means of a memory request.

Function sequence for display of fault messages 

If a fault is detected in the reversible emergency tensioning retractors, this is indicated on the multifunction display of the instrument cluster. Faults of other components that are part of PRE-SAFE are not displayed as PRE-SAFE faults.

Function sequence for 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 ESP control unit or the regenerative braking system control unit sends a signal to switch off the PRE-SAFE functions via chassis CAN.

The signal is transmitted to the control units involved through the central gateway control unit via the interior CAN.

The adjustment of the front passenger seat and the individual rear seats is canceled if the PRE-SAFE position has not yet been reached.

Closing of the windows and the tilting/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 tensioning retraction has been completed.

In the event of an impact that is detected by the restraint systems control unit, all adjustments are stopped immediately.

  PRE-SAFE, location of components Model 216 GF91.40-P-0001-01LA 
Model 221 GF91.40-P-0001-01LE
REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic, pre-safe Model 216 PE91.40-P-2051-97CAB
Model 221 PE91.40-P-2051-97SAB
  PRE-SAFE, block diagram Model 216 GF91.40-P-0001-03LA 
Model 221 GF91.40-P-0001-03LE
  Component description for instrument cluster A1
Model 216.3, model 221 (except 221.095/195)		 GF54.30-P-6000LE
Model 221.095/195 GF54.30-P-6000LEH
  Component description for front reversible emergency tensioning retractor A76, A76/1
Model 221		 GF91.40-P-4020LE
  DTR controller unit, component description On model 216 up to 31.8.10 with engine 156, 273, 275 and code (233) DISTRONIC PLUS Model 221 up to 31.8.10 with engine 156, 272, 273, 275, 642, 629 and code (233) DISTRONIC PLUS GF30.30-P-3210LE
On model 216 as of 1.6.09 up to 31.8.10 with engine 156, 273, 275 and code (233) Distronic Plus
Model 221 as of 1.6.09 up to 31.8.10 with engine 156, 272, 273, 275, 642, 629 and code (233) Distronic Plus		 GF30.30-P-3210LEB
On model 216.3 as of 1.9.10
With code (233) DISTRONIC PLUS
Model 221 (except 221.095/195) as of 1.9.10 with code (233) DISTRONIC PLUS or		 GF30.30-P-3210LED
  >Component description for restraint systems control unit N2/7 GF91.60-P-4048LE 
  Component description for rear SAM control unit with fuse and relay module N10/2 GF54.21-P-6030LE
  Rear seats control unit, component description N25/6
Model 221 with code (223) Rear bench seat with electrically adjustable outer seats with PRE-SAFE positioning function for outer seats and outer head restraints		 GF91.29-P-5250LE
  Component description for regenerative braking system control unit N30/6
On model 221.095/195		 GF42.22-P-1100LEH
  Right front seat control unit, component description N32/2 GF91.29-P-5240LE 
  Multicontour seat control unit (MCS), component description N32/15, N32/16
With code (409) Left/right multicontour seats		 GF91.25-P-5201LE 
    N32/20, N32/21
Model 221 with code (406) Rear multicontour seat		 GF91.25-P-5201LEA
  Dynamic seat control unit, component description N32/19, N32/22
On model 221 up to 31.5.09 with code (432) Left and right dynamic multicontour seat, on model 216 with code (432) Left and right dynamic multicontour seat		 GF91.25-P-5202LE 
  Component description for ESP control unit N47-5
Model 216.3, model 221 (except 221.095/195)		 GF42.45-P-5118LE
  Component description for radar sensors control unit N62/1
Up to 31.8.10 with code (233) DISTRONIC PLUS		 GF30.30-P-3301LE
  Video and radar sensor system control unit, component description N62/2
As of 1.9.10
with code (233) DISTRONIC PLUS, with code (238) Active Lane Keeping Assist		 GF30.30-P-3304LE
  Component description for left door control unit N69/1
Model 216		 GF72.29-P-4124LA
  Component description for left front door control unit N69/1
Model 221		 GF72.29-P-4141LE
  Component description for right door control unit N69/2
Model 216		 GF72.29-P-4128LA
  Component description for right front door control unit N69/2
Model 221		 GF72.29-P-4142LE
  Rear door control unit, component description N69/3, N69/4
Model 221		 GF72.29-P-6020LE
  Component description for overhead control panel control unit N70 GF82.20-P-5216LE
  Upper control panel control unit, component description N72/1 GF54.21-P-6040LE
  EZS control unit, component description N73 GF80.57-P-6003LE
  Component description for central gateway control unit N93 GF54.21-P-4170LE
  Component description for Weight Sensing System (WSS) control unit N110
Model 216 with code (494) USA version,
Model 221 with code (494) USA version As of 1.9.08		 GF91.60-P-4069LAU 
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