LEMON Manuals: Even more car manuals for everyone
Home >> Smart >> 2017 >> Fortwo Proxy, 2D Convertible, Standard Trans >> Repair and Diagnosis >> Restraints >> Restraints Control Systems >> Seats, Bunks, Restraint Systems - 453 Chassis >> Basic Knowledge >> Actuate Supplemental Restraint System, Function - GF91.60-P-2012KJ

Actuate Supplemental Restraint System, Function - GF91.60-P-2012KJ

MODEL 453.0/3/4 

except CODE 494 (US version) 

Function requirements for restraint system 

The status of circuit 15 of the ignition lock (S2) is received by the supplemental restraint system control unit (N2/10) from the vehicle interior fuse and relay module (F2) via a direct line.

Function requirements for power disconnect of high-voltage onboard electrical system in event of crash 

Supplemental restraint system (SRS) deployment, general 

The supplemental restraint system (SRS) continuously monitors the occupation status of the front passenger seat and the status of the seat belts (buckled or not buckled). It adapts its deployment behavior in accordance with the occupation status of the front passenger seat. The supplemental restraint system deployment function includes the following subfunctions:

Function sequence system monitoring 

When circuit 15 is switched on, the following indicator lamps are actuated:

Following a successful self-test (t = 4 s), the SRS indicator lamp is switched off. If the front passenger airbag is switched on, the front passenger airbag OFF indicator lamp is also switched off. The request to switch on the SRS indicator lamp is transmitted by the SRS control unit via the interior CAN (CAN B) to the instrument cluster. The front passenger airbag ON indicator lamp in the front passenger airbag warning indicator indicates when the front passenger airbag is switched on via the front passenger airbag shutoff switch (S68/15). If the front passenger airbag has been deactivated via the front passenger airbag shutoff switch, this is indicated by the front passenger airbag OFF indicator lamp. The front passenger airbag OFF indicator lamp and the front passenger airbag ON indicator lamp are actuated via direct lines by the SRS control unit. The SRS control unit continues to constantly monitor the SRS when driving and signals faults to the driver via the SRS indicator lamp. In vehicles with code K36 (instrument cluster with color 8.9 cm (3.5") display), in the event of a fault the warning "Fault: Service Required" is also displayed via the multifunction display (A1 p13) in the instrument cluster. The request to display the message is transmitted by the SRS control unit via the interior CAN to the instrument cluster. The faults are stored in the non-volatile memory of the SRS control unit.

Function sequence for evaluation of occupation status of front passenger seat 

The occupation status of the front passenger seat is determined via the front passenger seat occupation recognition (B41/1) and the front passenger airbag shutoff switch. However, only the status of the front passenger airbag shutoff switch has an influence on the deployment behavior of the SRS. If a child seat is being used, the front passenger airbag unit can be deactivated via the front passenger airbag shutoff switch.

IMPORTANT The occupation status of the front passenger seat, which is detected by the front passenger seat occupation recognition, has no influence whatsoever on the deployment behavior of the SRS. The status of the front passenger seat occupation recognition is only needed by the instrument cluster for the seat belt warning. Detailed information about the seat occupation recognition can be found in the separate subfunction "Passenger-side seat occupation recognition function".

Function sequence for detecting status of front seat belts 

The left front seat belt buckle switch (S68/1) or the right front seat belt buckle switch (S68/2) is actuated when the seat belt tongue is inserted into the seat belt buckle. The status of the front seat belt buckle switches is read in by the SRS control unit directly and made available to the instrument cluster for the seat belt warning via the interior CAN. The status of the front seat belt buckle switch has no influence on the deployment of the front seat belt tensioners, which are always triggered independently of this, provided that the relevant triggering conditions exist.

IMPORTANT Detailed information about the seat belt warning can be found in the function description "Instrument cluster (IC) function".

Function sequence for detecting the status of the rear seat belts (model 453.0) 

The left rear seat belt buckle switch (S68/11) or the right rear seat belt buckle switch (S68/12) is actuated when the seat belt tongue is inserted into the seat belt buckle. The status of the rear seat belt buckle switches is read in by the SRS control unit directly and notified to the instrument cluster for the seat belt warning via the interior CAN. The status of the seat belt buckles in the rear does not have any influence on the deployment characteristic of the SRS. The rear seat belt tensioners are always triggered.

Function sequence for impact detection 

The SRS control unit uses the following sensors to determine the acceleration forces acting on the vehicle:

The sensor signals are read in directly by the SRS control unit. A distinction can be made between the following types of impact by evaluating the signals of these sensors:

Function sequence for frontal impact 

A frontal impact is detected by the SRS control unit via the integrated sensors. The deployment of the restraint equipment takes place depending on the impact velocity, the severity of the impact and the position of the front passenger airbag shutoff switch.

The following squibs can be ignited:

IMPORTANT In vehicles up to and including model year 2016 and in national versions for the Economic Commission for Europe (ECE), code 294 (kneebag) is standard equipment for the driver.

No restraint equipment is usually deployed up to an impact velocity of 15 km/h. No restraint equipment is deployed at an impact velocity between 15 km/h and 26 km/h depending on the impact, or in the case of more severe events the seat belt tensioners are ignited together with the driver airbags and the front passenger airbag (prerequisite: front passenger airbag shutoff switch in position "ON").

As of an impact velocity of 26 km/h, the driver airbags and the front passenger airbag are deployed together with the seat belt tensioners, and the squibs of the following airbags may also be ignited depending on the impact and the angle of impact:

The squibs are directly actuated by the SRS control unit.

The following situations are taken into account:

The SRS control unit decides whether to suppress or deploy the front passenger airbag on the basis of the current switch position.

Function sequence in the event of a side impact 

A side impact is detected by the SRS control unit by evaluating the signals of the following sensors:

The deployment of the restraint equipment takes place depending on the severity of the impact, the occupation of the front passenger seat and the status of the seat belts.

The following squibs can be ignited (at most):

The squibs are directly actuated by the SRS control unit.

Function sequence for rear impact 

A rear impact is detected by the SRS control unit via the integrated sensors. The restraint equipment is deployed depending on the severity of the impact.

The following squibs are ignited:

The squibs are directly actuated by the SRS control unit.

Function sequence for rollover 

A rollover is detected by the SRS control unit via the integrated sensors. When the rollover occurs, the SRS control unit transmits the crash signal via the interior CAN. The hazard warning lamp is then activated, and opening of the central locking (CL) is initiated.

IMPORTANT Detailed information can be found in section "Function sequence for additional functions in the event of a crash".

Function sequence for additional functions in the event of a crash 

Function sequence for activation of hazard warning lamp 

In the event of airbag deployment the SRS control unit transmits an appropriate crash signal via the interior CAN to the center SAM control unit (N10/10). As master indicator, this triggers the hazard warning lamp.

IMPORTANT Detailed information about the hazard warning lamp can be found in the separate function description "Exterior lighting function" in subfunction "Turn signal light actuation function".

Function sequence for opening the central locking (CL) 

The central locking is unlocked automatically following a crash event. To do this, the SRS control unit transmits the crash signal via the interior CAN to the center SAM control unit, which then initiates unlocking of the doors and flaps.

In order to unlock after a crash event, the center SAM control unit actuates the following actuators:

IMPORTANT Detailed information about central locking (CL) can be found in the "Central locking (CL) function" subfunction of the separate function description "Anti-theft protection and locking function description".

Function sequence for switching off engine and fuel feed with restart refusal (except model 453.091/391/491) 

In order to avoid the potential risk of fire after an accident, the engine is turned off automatically. Depending on the severity of the crash event, the SRS control unit initiates a fuel feed shutoff and restart refusal. To do this, the SRS control unit transmits the crash signal via the interior CAN to the ME control unit (N3/10), which shuts the engine off. Depending on the crash signal message, actuation of the ignition coils/fuel pump actuation relay (F11k3) is suppressed by the ME control unit and therefore the power supply for the following engine management actuators is shut off:

Depending on the crash signal message, actuation of the circuit 87 engine function relay (F11k1) is suppressed, which also deenergizes the fuel injection system of the engine. In order to be able to start the engine again after the crash event, the fault memory in the ME control unit must be deleted using XENTRY Diagnostics after checking the components. Otherwise, it is not possible to restart the engine after a severe crash event.

Function sequence for switching off electric drive and power disconnect of high-voltage on-board electrical system with restart refusal (only model 453.091/391/491) 

In the smart E-Drive, various safety shutoff functions on the high-voltage drive and high-voltage on-board electrical system are performed in a crash event. The function sequence for switching off the electric drive and for power disconnect of the high-voltage on-board electrical system with restart refusal is split up into the following subfunctions:

Switch off drive motor for electric vehicle 

Additional triggering condition

If a crash or a rollover occurs during driving or when the vehicle is stationary, with the drivetrain switched on, the SRS control unit initiates a shutdown of the electric drive when in the operating condition (circuit 15 ON). To do so, the SRS control unit sends the crash signal via the interior CAN to the electric drive control unit (N127). The electric drive control unit initiates the shutdown of the electric vehicle drive motor.

IMPORTANT Detailed information on the high-voltage drive and the high-voltage on-board electrical system is available in the separate function description "Electric drive function".

Power disconnect of high-voltage on-board electrical system  Additional triggering condition

In the case of a medium or severe accident, the high-voltage on-board electrical system must be disconnected and thereby de-energized. To do this, the high voltage output of the high-voltage battery (G5) can be disconnected from the high-voltage on-board electrical system using the contactors actuated by the electric drive control unit. The contactors are located in the high-voltage battery. In the operating condition (circuit 15 ON), the SRS control unit initiates shutoff of the high-voltage on-board electrical system if a crash or rollover occurs during driving or when the vehicle is stationary; when the vehicle is stationary (circuit 15 ON or OFF), this is done by the high-voltage crash sensor control unit (N2/1) (as a backup for the acceleration sensor in the SRS control unit). To do so, the crash signal is sent by the SRS control unit via the interior CAN or the high-voltage crash sensor control unit via the electric drive CAN (CAN EL) to the electric drive control unit. The electric drive control unit disconnects the high-voltage on-board electrical system from the high- voltage battery by opening the contactors within 50 ms. Any attempt to restart the drive system initiates insulation monitoring by the battery management system control unit (N82/2). The measured value is sent via the electric drive CAN by the battery management system control unit to the electric drive control unit where it is then evaluated. If a specific resistance value is undershot, e.g. after a slight or medium crash event, the contactors are not switched by the electric drive control unit, and charging the high-voltage battery or restarting the drive system is not possible.

Termination of DC/DC converter control unit voltage conversion 

Additional triggering condition

In the event of a crash or rollover in operating condition, the voltage support of the 12 V on-board electrical system is stopped via the DC/DC converter control unit (N83/1). To do this, the power electronics control unit (N129/1) transmits the signal for switching off the DC/DC converter control unit to the DC/DC converter control unit via the electric drive LIN to stop the 12 V on-board electrical system voltage supply. Within a period of 50 ms, an active voltage conversion by the DC/DC converter control unit is stopped. The power supply via the 12 V on-board electrical system battery (G1) (e.g. for the hazard warning system) remains active.

Termination of active charging process 

Additional triggering condition

If the charging process monitoring control unit (N83/2) (except code 908 (on-board charger 22 kW)) or the charger control unit for the high-voltage battery (22 KW charger) (N83/10) (with code 908 (on-board charger 22 kW)) receives the crash signal from the SRS control unit via the electric drive CAN from the electric drive control unit or the crash signal from the high-voltage crash sensor control unit when the vehicle is stationary, it immediately initiates the termination of an active charging process for the high-voltage battery within 50 ms.

High voltage rapid discharging in the event of a crash 

Additional triggering condition

In addition to disconnecting the high-voltage on-board electrical system from the high-voltage battery, the SRS control unit, together with the high-voltage crash sensor control unit, initiates a high-voltage rapid discharge of residual capacities in the event of a crash or a rollover during driving in operating condition (circuit 15 ON); when the vehicle is stationary (circuit 15 ON or circuit 15 OFF), this is done by the high- voltage crash sensor control unit. To do so, the crash signal is sent by the SRS control unit via the interior CAN or by the high-voltage crash sensor control unit via the electric drive CAN to the electric drive control unit. The electric drive control unit then sends the request for rapid discharge in the crash signal via the electric drive CAN to the power electronics control unit. The power electronics control unit then initiates the high-voltage rapid discharge process. In the event of a crash, the high-voltage on-board electric system is discharged to a voltage of < 60 V by the electric drive within 5 seconds. The energy is converted into heat in the stator coil of the electric vehicle's drive motor.

Restart refusal for electric drive 

Additional triggering condition

Depending on the severity of the crash event and the crash signal message, the SRS control unit or the high-voltage crash sensor control unit initiates a power disconnect of the high-voltage on-board electrical system and a restart refusal for the drive system. To restart the high- voltage drive following a severe crash event, the fault memory of the electric drive control unit has to be cleared using XENTRY Diagnostics after the components have been checked. Otherwise, the electric drive cannot be restarted following a severe crash event.

  Electric function schematic for deployment of supplemental restraint system Model 453 (except 453.091/391/491) PE91.60-P-2055-97BBA 
Model 453.091/391/491 PE91.60-P-2055-97BEU 
  Overview of system components for supplemental restraint system   GF91.60-P-9996KJ 
scientia non olet · About LEMON Manuals