204207 - AIR BAG SYSTEM

VIEW OF ASSEMBLY

The following figure shows the complete Air Bag system configuration

INTRODUCTION

The airbag system fitted to the car is activated following moderate to severe front or side impact to protect the occupants. The sidebags and window bags protect the chest and head respectively. In the case of the rear passengers, this protection is guaranteed only to side seat occupants.The system is complemented by front and side rear seat belt pretensioners. These are fitted with load limiters to optimise the restraining action.It is NECESSARY for seat occupants to wear their seat belts correctly to ensure the air bags work to maximum effectiveness.
Air bag system components are designed to work on a specific vehicle. They therefore CANNOT be tampered with, adapted or installed on other types of vehicle. Any attempt to reuse, adapt or install on another type of vehicle may cause severe or fatal injury to car occupants during normal use or in the case of impact.
A control system controlled by an electronic control unit controls partial or total device activation in the case of front or side impact.The electrical connection between air bag components is via wiring. This is built into the facia wiring harness in the case of front devices and into the rear wiring harness in the case of side devices.The control unit is connected to the system via two connectors, one for the front lead and the other for the rear lead.The front airbag module on the passenger side may be deactivated voluntarily by means of a special key-operated switch on the side of the facia. Front passenger side airbag module deactivation does not disable the sidebag modules. This means that any children carried in the car are protected against side impact.Rear sidebag modules may be deactivated voluntarily by means of a special switch in the right hand side of the boot near the power point.
The car must be handed over to the customer with the passenger airbag deactivation switch in ON position and control panel warning lights off. The rear side bag deactivation switch must be in OFF position and the warning light on the control panel on.
For safety reasons, NO continuity checks can be carried out on the wiring. See E7030 to consult the system connection wiring diagram.
GRAVE DANGER! The front airbag module MUST be deactivated if a child seat is fitted to the front passenger seat.
If the module is deactivated, the front seat passenger is protected only by the seat belt with pretensioner and sidebags in the case of a crash.
Airbag activation releases a small amount of powder. This powder may be deposited on unfolded bags and inside the car. It is not harmful but may irritate the skin and eyes. Wash with neutral soap and water in the case of exposure.
The airbags may go off if the car is exposed to strong impact or incidents that affect the underbody, e.g. violent knocks against kerbs and ridges in the ground - or if the car drops into big holes or ditches.
Observe the regulations if the car is scrapped [PR5580C].
The following indications show the system is working properly:

  • fault warning light (red) on the control panel:
  • passenger side airbag disabled warning light (yellow) on the instrument panel;
  • rear side bag disabled warning light (yellow) on the instrument panel;
  • tester input, K line built into the EOBD intake, to check operation using an EXAMINER.
If the car changes owner, the new owner must be made aware of the user instructions and warnings shown above and must be given the Car Owner's Handbook

COMPOSITION

The airbag protection system comprises:

  • An electronic control unit;
  • four side impact sensors (two on the right and two on the left) located in the side and rear pillars;
  • a passenger airbag disablement switch;
  • a rear sidebag disablement switch;
  • two frontal protection airbag modules for front seat occupants;
  • a person presence sensor on the front passenger seat;
  • four side protection sidebags (chest, abdomen) for front and rear side seat occupants;
  • four side protection head bag modules (head) for front and rear side seat occupants;
  • four seat belts with pretensioners on the front and rear side seats;
  • seat belts and accessories.

Electronic control unit

The electronic control unit is positioned beneath the central tunnel.

Specifications

The electronic control unit manages the entire system and controls all its components. It is designed to recognise an impact situation in plenty of time to activate the pretensioners alone or the pretensioners plus the air bag modules according to impact severity and type.The control unit is rigidly secured to the body beneath the central car consule near the centre of gravity. This location allows interior deceleration sensors to detect car deceleration with accuracy.
The control unit must always be fitted with the arrow printed on the adhesive plate facing in the car's direction of motion. Always check for foreign bodies between the control unit and body and tighten the bolts to the specified torque.

Composition

The following diagram shows the control unit.
The control unit contains two deceleration sensors, one electronic and one electromechanical safety sensor that activates an activation enablement function independently of the electronic sensor.If the car deceleration level detected by the electronic sensor and processed by the ECU in terms of impact severity, exceeds the severity level set for the device deactivation control, the control unit allows the command to be sent only if the safety sensor is closed at the same moment.The following functions are present to ensure the system is correctly managed:

  • energy accumulation: the control unit is supplied at 12V with the key ON but can still operate for a few fractions of a second if the power supply is cut off or experiences a voltage drop in order to safeguard system operation and write the data in the crash memory.
  • check earth fastening: the control unit software checks the electrical contact between body and control unit;
  • fault memory: with the key ON, the control unit continuously monitors circuit operation (including energy reserve circuits) during normal vehicle operation and impacts. It also diagnoses all electrical parts of the system and indicates the presence of faults by turning on an airbag system fault warning light on the instrument panel and saving the fault code.
  • crash memory: records information on crash events that trigger activation of the pretensioners and front or side modules.
Because it is so important, the control unit is designed so that it cannot be opened without leaving visible signs of tampering.
If the control unit falls to the ground or is subject to abnormal knocks during handling, it MUST be replaced.

Operation

In case of frontal impact, the electronic sensor detects a deceleration signal along the car's longitudinal centre line. If the signal processed by the processor inside the control unit indicates an impact severe enough to require system intervention and if, at the same time, the safety sensor is closed (activation enabled), the control unit controls activation of the pretensioners along as an initial intervention level. In the case of more severe impact, it controls activation of the pretensioners and front airbags (activation of the driver module alone if the passenger side module is deactivated or without a passenger present).The front airbags feature double-stage activation, i.e. a reduced explosive charge is set off with low impact energy while complete activation takes place if the protection requirement is maximal.Similarly, when side impact occurs, the control unit is able to recognise direction and intensity and thus activate the three airbags present on the side affected by impact. Four sensors, two on each side, are present along the entire length of the passenger compartment to provide full coverage against side imact. These are located in the front and rear pillars.These sensors are designed to detect side impact at a very early stage, process the signal and send a pulse to the control unit that further processes the signal and decides whether to set off the airbags or not.System activation times are in the order of thousandths of seconds and are so fast that occupant body movements can be anticipated following impact.After each activation of one of the controlled systems (pretensioners, front airbags, sidebags), the control unit stores the activation in its permanent memory and controls activation of the fault warning light on the instrument panel.Before it is replaced, the control unit guarantees activation of individual devices within the following limits:

  • 3 impacts with activation of front seat belt pretensioners alone;
  • 3 impacts in total with side bag activation (right or left);
  • 1 impact with activation of pretensioners and front airbags (even if only one stage is activated);
  • any combination of the above situations until one of the limits indicated is reached.
If one of the limits described is not reached, it will be possible to reuse the control unit after carrying out the RESET procedure using the EXAMINER once system operating conditions have been restored. The last activation for each of the sequences will prevent further reset procedures.
The airbag system does not cut if the car is shunted or rolls over.

System self-diagnosis

The control unit carries out continuous self-diagnosis of system operation. More specifically:

  • it detects and stores faults;
  • it recognises the various components and the fault type;
  • it indicates the source of these fault by turning on an instrument panel warning light.
Faults stored in the control unit may be deleted only after the fault has been repaired by means of the EXAMINER device.
if a fault is detected in the passenger airbag disablement switch, the control unit treats is as though it is off for safety reasons and the instrument panel warning light is turned on.

Air Bag system fault warning light

Specifications

At key ON, the fault warning light (red) comes on for about four seconds (initial self-diagnosis stage) and then goes off. If the control unit detects a fault in the warning light, it saves the corresponding fault code. If no system faults are detected at key on and no fault conditions are present in the fault memory, the warning light goes off after four seconds of self-diagnosis. Otherwise it stays on until key off.

Operation

The warning light stays or comes on durng normal car operation in the following cases:

  • the control unit detects a fault in the airbag system;
  • the control unit detects a crash with system activation;
  • when a fault is detected in the warning light connection circuit.
As a consequence of a crash when the pretensioners or sidebags alone are activated, the warning light stays on until system operating conditions are restoered (replacement of affected part or control unit repair using an EXAMINER).If the crash causes the front airbag modules to activate, the warning light stays on permanently because the control unit cannot reset (in this case the control unit must be replaced).If internal operating errors occur during the operational lifetime of the control unit that cannot be repaired during the EXAMINER, this are indicated by permanent activation of the warning light.

Front passenger Air Bag disabled warning light

Specifications

With the key ON, the yellow passenger side air bag disabled warning light comes on for about four seconds (initial self-diagnosis stage). If the control unit detects a fault in the warning light, it saves the fault code, turns on the fault warning light and maintains the passenger side airbag module disabled. System operation is restored by means of an EXAMINER as with the fault warning light.Once the initial self-diagnostic stage of 4 seconds has elapsed, if the key-operated disablement switch is turned OFF, the warning light stays on to indicate (passenger module disabled). If no faults are present, the warning light flashes for another four seconds and then goes off to indicate (passenger module enabled).
The passenger side module MUST be disabled only with the ignition key (ignition key OFF) - (DO NOT USE a second ignition key to disable).

Driver's Air Bag module

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