Gas generator
There is a gas generator in every airbag module. The gas generator is a sealed unit made of aluminum or steel. This contains a propellant that forms a harmless gas. As was mentioned earlier the airbag inflates very rapidly.
Scheme 34
The connector between the SRS ignition cable and airbags/seat belt tensioners has a built in capacitor (1). The capacitor is connected in series with one of the cables. Resistance cannot be measured between sockets (3) and (4) as the capacitor blocks measurement. There is an "service hole" (2) in the connector to facilitate fault tracing.
The built in capacitor prevents the unintentional triggering of the igniter due to the unintentional connection of a DC voltage to the SRS ignition cable.
Repairing SRS cabling
| WARNING | SRS cabling must not be repaired or spliced and individual cables may not be replaced. If there is a fault in the cabling the SRS ignition cable and/or cable harness must be replaced. |
Scheme 35
The SRS system connectors are color coded.
The connector between the SRS ignition cable and airbags/seat belt tensioners is green.
Scheme 36
The connector on the SRS ignition cable to the contact reel is green.
Scheme 37
The connector on the passenger module SRS ignition cable is red.
Scheme 38
The SRS sensor module has a on board diagnostic (OBD) system for providing self diagnosis and other information, which can be read off using the Volvo Scan Tool (ST) connected to the data link connector (DLC).
Location of the data link connector (DLC)
The data link connector (DLC) is located in the center console by the cigarette lighter tray.
Scheme 39
The driver and front seat passenger seat belts are each equipped with a pyrotechnical seat belt tensioner.
These seat belt tensioners have a gas generator with an electrical igniter (C) connected to a cylinder. In cylinder (D) is a piston with a wire, one end of which is wound around a drum connected to the belt reel.
An electrical signal from the sensor module activates the gas generator and the gas produced drives down the piston in the cylinder. The cable is tightened and rotates the seat belt reel, taking up any slack in the seat belt. The tensioner can take up a maximum of 9 cm (3.5") of slack.
| WARNING | Seat belt tensioners must never be disassembled, repaired or transferred to another vehicle. |
If the car is to be scrapped or the seat belt tensioners removed, see Handling non-deployed airbag modules/pyrotechnic seat-belt tensioners .
Note. Volvo recommends that seat belt tensioners be replaced every 10 years to maintain reliability.
Scheme 40
The sensor module is either adapted for SRS systems with one (driver's side) airbag or two airbags (on the driver's and passenger sides) and is also adapted for the model. To prevent the wrong sensor module being installed during replacement the sensor module is both color and physically coded as follows.
The connector between the SRS cabling and the sensor module is color coded with the same color as the sensor module connector.
The sensor module connector is physically coded with a stop lug (contact code) on the connector sleeve.
- SRS system 800 1996 with 1 airbag (driver's side) has contact code A and color code Black.
- SRS system 800 1996 with 2 airbags (driver's and passenger side) has contact code B and color code Blue.
Scheme 41
A decal on top of the sensor module displays the sensor module P/N (beneath the Volvo logo), contact code (in a box) and serial number in digits (at the bottom) and as a bar code.
The serial number is made up of production year (2 digits), production day (3 digits), serial number (4 digits) and contact code (letter).
General
The sensor module contains the following
- Twin piezoelectric sensor elements which detect deceleration/collision signals.
- Microprocessors which evaluate collision signals and activate the airbags and pyrotechnical seat belt tensioners.
- A memory function which stores system fault information even when power has been interrupted (which facilitates fault tracing).
- Back up power unit.
Miscellaneous
Even if the sensor module detects a fault to one igniter, and stores a diagnostic trouble code (DTC), it will still try to activate all igniters in the event of a collision.
In the event of a collision in which the SRS system is activated, the sensor module stores all data about the system at the moment of the collision.
If supply voltage is too low or too high (<<9 V and >>18.5 V) the indicator lamp will light at the same time as the sensor module goes into standby mode. As soon as the voltage is correct, the warning lamp goes out after 10 seconds and the system operates normally. The sensor module cannot store any of the 19 diagnostic trouble codes (DTCs) if supply voltage is too low or too high. There is no separate SRS diagnostic trouble code (DTC) for supply voltage too low or too high. If the supply voltage is too low or too high the Volvo Scan Tool (ST) cannot communicate with the sensor module.
If D+ voltage is too low <0.7 V, the SRS warning lamp will light when the ignition is in position II.
Electrical signal for activating airbags/seat belt tensioners
To activate the igniters that deploy the airbags/seat belt tensioners, the sensor module transmits pulses in the form of AC signals through the ignition cables. At least 5 pulses are required to trigger an igniter.
A capacitor, built into the connector between the SRS ignition cable and the airbags/seat belt tensioners, allows this pulsing signal to pass through it while blocking a DC signal.
This means that connected airbags/seat belt tensioners in the SRS 6.2 system cannot be activated by unintentionally connecting a DC voltage during fault tracing. This protection ceases when the SRS ignition cable connector is disconnected from the airbag/seat belt tensioner, as the capacitor is in the SRS ignition cable connector.
| WARNING | Under no circumstances use an ohmmeter or other live measuring instrument to take readings on a disconnected non deployed airbag/seat belt tensioner. This could deploy the airbag/seat belt tensioner. |
Scheme 42
SIPS bag is a separate system in each front seat. There is no connection between the SIPS bag in both of the seats. Depending on the collision process the SIPS bag is detonated in the seat on the collision side. The sensor unit has a pyrotechnical impact sensor, which in order to detonate the system, must be hit with a force that gives a speed of 2 m/s against the sensor unit by the deformed door. The limit values are set to avoid unintentional detonation, for example, when the door is hit or minor impact against a stationary object.
The pressure plate deforms the aluminum case, whereby an impact pin is pushed in and triggers the detonator. The detonator generates a pulse which is transferred to the igniter cables as a detonation wave. When the detonation wave reaches the cushion module it activates the charge of powder in the gas generators.
On activation the gas is first blown into a combustion chamber pipe and the gas then flows out into the cushion. Activation of one of the gas generators occurs immediately and the other is activated with a delay of about 3 milliseconds. The delay is set to maintain the inflated cushion's pressure and volume for a sufficiently long time.
On inflation the cushion breaks the cushion module's casing, tears the seat upholstery's seam and is forced out to inflate to full volume. The cushion is inflated in the direction of the door side to contribute toward the protection of the person's chest in the event of a collision. Ventilation through holes in the cushion's fabric is adapted so the cushion deflates at an appropriate rate to slow the driver/passenger.
There is not diagnostic system or warning lamps connected to the SIPS bag.
The SIPS bag is only installed in vehicles that are equipped with an SRS system and always fitted in both front seats.
Scheme 43
Sensor unit components
4. Sensor housing
5. Aluminum casing
6. Spring washer
7. Impact pin
8. Compression washer
9. Detonator
10, Transport lock
Cushion module components
11. Cushion
12. Gas generators
13. Combustion chamber
14. Installation bracket
Scheme 44
SIPS bag is activated with a specific side impact against the front door and then contributes to improved protection for the occupants of the front seats.
SIPS bag were introduced as standard on some markets and as an option on others, from model year 1995.
SIPS bag placed in the front seat
The SIPS bag consists of three main parts
- 1. Sensor unit
- 2. Igniter cable
- 3. Cushion module
Note. The pictures in the service information only show the left-hand front seat. The SIPS bag components for the right-hand seat are identical, with the exception of the pressure plate (in front of the sensor unit) which comes in right and left-hand designs.
Scheme 45
The sensor unit is positioned in a sensor bracket in the front SIPS pipe's outer end. Placement is the most protruding part of the seat against the inside of the door.
A pressure plate is mounted in front of the sensor unit. On side impact the pressure plate captures and distributes forces from the door's inner panel to the sensor unit.
Igniter cable
The igniter cable, which is of a pyrotechnical type, is routed in the back of the seat and under the seat cushion.
The igniter cable consists of two hoses that are coated with a pyrotechnical material on the inside. On detonation the signal is effected as a detonation wave.
The outside of the hoses are coated with a common, black protective sheath, which protects the hoses against mechanical damage.
Scheme 46
The cushion module is placed on the backrest frame to contribute to protect where the driver's/passenger's chest is closest to the door's inner panel.
Cushion
The cushion, which is manufactured of silicone coated polyamide fabric , is folded under a cover. When inflated the cushion has a volume of approximately 12 liters.
Gas generators
Two gas generators are used to inflate the cushion. On activation the gas generators produce a harmless gas that inflates the cushion very quickly.