Safety and general procedures
Airbags and pyrotechnic pretensioners are safety devices, but as they contain explosives they are capable of causing injury if mishandled.
Always refer to model-specific information before starting work on an SRS system and observe the following recommendations.
Disarming
NOTE: In the case of an emergency, involving a model not covered in this product, the following guidelines can be followed. However there are certain systems that can only be deactivated by using specialist equipment.
•Ensure that any electronic codes are recorded (i.e. radio code).
•Switch ignition OFF.
•Remove ignition key.
•NEVER connect a battery powered 'memory saver' unit.
•Disconnect all battery leads, ensure that accidental reconnection is not possible.
•Wait at least 30 minutes.
•Mechanically lock pretensioners (where applicable).
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Arming
•Ensure vehicle interior is unoccupied before arming the system.
•Ensure ignition switched OFF.
•Reconnect all battery leads.
•Switch ignition ON.
•Check SRS warning lamp operation, if lamp fails to illuminate, illuminates and remains on or flashes this indicates a fault in the system.
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After deployment
NOTE: The metal parts of the airbag and pretensioner will be very hot after deployment and 20-30 minutes should be allowed before touching any of them.
WARNING: Wear gloves and eye protection when working on deployed airbags as the chemical residues can cause skin irritation. Wipe affected areas of the vehicle with a damp cloth or clean with a vacuum cleaner. Any areas of skin that come into contact with deployed airbags should be washed with soap and water.
Check the following
•Windscreen for smoke or heat damage.
•SRS wiring harness and connectors for charred or damaged areas.
•All SRS mounting brackets.
•All SRS components including undeployed airbag(s)/pretensioner(s).
•Fascia/instrument panel.
•Seat assemblies.
•Seat belts, including buckles and anchorage points.
•Steering wheel and column.
•Surrounding components and trims.
•SRS control module and bracket.
•SRS control module fault memory.
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Slip ring
•Some models (usually with only a driver's airbag) have a slip ring connecting the steering wheel to the vehicle harness.
•The slip ring comprises a fixed circular contact ring and a moving contact (attached to the steering wheel).
•The slip ring has unlimited rotational movement and therefore does not require centralising when the steering wheel is removed and replaced.
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Spiral cable ('clock spring')
•This component provides a permanent connection between the airbag assembly and the rest of the SRS system.
•The spiral cable assembly is a two-piece moulding [1] with a flexible, coiled connection between the two parts [2].
•One part is fixed to the steering wheel and the other part to the outer steering column, with a limited (usually 6-7 turns) rotational movement.
•The spiral cable assembly must be centralised with the road wheels in the straight-ahead position, otherwise when the steering is turned one way the cable will be strained and eventually break.
•In cases where the central position has been lost and there are no obvious alignment marks [3], the following procedure can be carried out (with the steering wheel removed):
•Turn clockwise until resistance is felt.
•Turn anti-clockwise and count turns, until resistance is felt.
•Turn clockwise half the number of turns noted in the previous operation.
•Refit the steering wheel, ensuring that the spiral cable does not move.
•If in any doubt a new replacement unit should be fitted.
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Safety precautions
Carefully inspect all components for damage, such as cracks, dents or evidence of being dropped. Any damaged components should be disposed of safely.
Check for signs of contamination, such as water or oil, before installation. Any contaminated components should be disposed of safely.
•NEVER carry out resistance checks on SRS components, undeployed airbags or pyrotechnic pretensioners.
NOTE: If a trouble code is logged and the probable cause is a high or low resistance, trouble shooting should NOT be carried out with an ohmmeter. Any faulty components should be replaced with new items.
•NEVER attempt to repair SRS wiring.
•NEVER attempt to repair any SRS component.
•NEVER connect an external electrical supply to SRS components.
•NEVER connect earth wiring from other electrical circuits to SRS component mounting screws.
•NEVER install accessories (e.g. such as car phones, drinks holders, cassette racks etc.) in the area of the passenger's airbag, as they could become detached and blown backwards by the force of deployment.
•NEVER allow pyrotechnic pretensioners to come close to strong magnets.
•NEVER store or carry undeployed airbags in the passenger compartment of a car.
•NEVER leave undeployed airbags or pretensioners unattended.
•NEVER use universal covers on seats incorporating side airbags.
•NEVER transfer SRS components from one car to another - ALWAYS use genuine new components.
•NEVER attempt to dismantle components, especially airbags and seat belt pretensioners.
•ALWAYS disconnect ALL pyrotechnic devices before attempting to check SRS wiring continuity.
•ALWAYS use a digital multi-meter for checking wiring continuity and voltage. NEVER use an analogue test meter or test lamp on an active SRS system, as this could cause accidental deployment of airbags and/or pretensioners.
•ALWAYS ensure all multi- plugs are correctly inserted and securely locked together.
•ALWAYS ensure all wiring is correctly routed and secured to avoid chaffing, trapping or shorting the harness.
•ALWAYS install airbags and pyrotechnic pretensioners as soon as possible after removal from their special packaging.
•ALWAYS use the correct fixing bolts for SRS components.
•ALWAYS disconnect the battery before any welding operations and connect the earth terminal of the welder as near to the welding area as possible.
•ALWAYS disconnect or remove the SRS control module when welding in the immediate area.
•ALWAYS disconnect or remove the side airbag sensor when welding the door.
•ALWAYS record the date of fitting a replacement airbag or pyrotechnic pretensioner.
•ALWAYS register the replacement by using the registration card or bar code etc. supplied with the new components.
•ALWAYS remove pretensioners if the vehicle temperature is likely to be above 110°C.
•ALWAYS remove airbags if the temperature is likely to be above 85°C.
•ALWAYS remove the SRS control module if the temperature is likely to be above 100°C.
•ALWAYS observe torque figures,overtightened or loose components could affect the operation of the airbags and pretensioners.
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Temporary storage
NOTE: Incorrect handling and storage can render airbags and pretensioners inoperative.
If airbags or pyrotechnic pretensioners are stored overnight they must be kept in an approved secure steel cabinet (registered with the local council) as they are legally classified as explosive items - refer to Storage and handling.
•ALWAYS keep components dry.
•ALWAYS carry and store airbag assemblies with the pad surface uppermost.
•ENSURE nothing is resting on the airbag assembly.
•PROVIDE a secure, designated storage area for SRS components, especially airbags and pretensioners.
•NEVER twist, knot, hang up, crush, squeeze, pinch or squash head airbags.
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Rescue and recovery
Towing
•Recovery of a vehicle with airbags that have not deployed is most unlikely to result in inflation of an airbag, but as a safeguard both battery leads should be disconnected and taped over to prevent reconnection.
Rescue - airbag(s) deployed
•No harmful substances (either gases or solids) are left as a consequence of airbag deployment. Any white residue is basically talcum powder to aid the sliding properties of the airbag material.
•The chemicals within the gas generator are sealed within a water-tight container and therefore all types of fire extinguisher are suitable for use on vehicles fitted with deployed airbags.
•Identification: SRS components are normally identified externally either by a moulded SRS or Airbag logo (in the case of airbag covers), and also by warning labels attached to one or more of the following: sun visor, door shut, glove box lid, side of fascia, side of seat base, B post and individual components.
•Deployed airbags do not need to be covered, folded or removed. They can just be lifted out of the way.
•Deployed airbags are harmless to the occupants and rescue services.
•Slight skin grazing can be caused to occupants in contact with airbags during deployment.
Rescue - airbag(s) not deployed
•Check if the vehicle has airbag(s) fitted - refer to vehicle-specific chapters for warning label locations.
•If possible, work outside the area of airbag deployment.
•If it is necessary to cut electrical wiring or remove components by force, unintentional triggering of SRS components is always possible.
•Ensure the ignition is switched OFF.
•Move seats as far back as possible.
•Disconnect all battery leads (earth lead first) and ensure that accidental reconnection is not possible.
•If the battery terminals are inaccessible cut through all battery leads (earth lead first).
•If possible wait to allow capacitor(s) to discharge.
•Avoid drilling or cutting the airbag assemblies.
•Avoid excess heat in the area of the airbag assemblies.
•In the case of a vehicle fire, the heat may eventually trigger deployment, which will occur in the normal way. The gas (mainly Nitrogen) is inert and there is no possibility of an explosion.
•The chemicals within the gas generator are sealed within a water-tight container and therefore all types of fire extinguisher are suitable for use on vehicles fitted with undeployed airbags.
This is from AD tech topics, I think you will agree correct information is essentail to repairing modern vehicles,you should have a subscription with at least one inforamtiom provider.
Cheers Aidan
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