The Supplemental Restraint System (SRS) is the complete network of airbag sensors, control modules, and airbag inflator assemblies that supplement the seatbelts to protect occupants during a collision. A modern vehicle may contain 6–12 or more airbag modules in specific locations: driver and passenger frontal airbags in the steering wheel and dashboard, side-curtain airbags that deploy from the roof rail to protect heads during side impacts, seat-mounted side torso airbags, knee airbags, and increasingly, far-side airbags. The SRS control module continuously monitors impact sensors (accelerometers) positioned throughout the vehicle body and at each airbag location, and makes a deployment decision within 15–30 milliseconds of impact detection. The deployment threshold is calibrated to distinguish a genuine crash from a pothole, kerb impact, or minor parking collision. Airbag inflators use a precisely measured pyrotechnic charge to fill the airbag with nitrogen gas from a folded position to full deployment in approximately 30 milliseconds — faster than the human eye can detect. Once deployed, airbags deflate within 1–2 seconds through vent holes, clearing the occupant's vision for post-crash response. Airbags must be replaced after deployment — an inflator is a single-use component. The SRS warning light indicating a fault must be diagnosed and repaired immediately — a fault in the SRS system can cause airbags to fail to deploy in a genuine crash or (rarely) to deploy unexpectedly.
Airbags work in conjunction with seatbelts, not as a replacement for them. Seatbelts arrest the forward motion of the occupant's torso; the airbag creates a deformable cushion that prevents the head from striking the steering wheel, dashboard, or A-pillar at speed. Without the seatbelt holding the torso in position, the airbag cannot effectively protect the head — an unbelted occupant may deploy the airbag but still sustain serious injury from contact with the deploying bag at high speed. The SRS module's deployment decision considers multiple inputs simultaneously: the severity of the deceleration, the direction of the impact, the occupant presence sensors (to avoid deploying a passenger airbag when the seat is unoccupied), and the seatbelt buckle sensors (which confirm belt use and may reduce deployment threshold when the belt is not fastened). After any airbag deployment, the entire SRS system requires professional assessment — the deployed airbags must be replaced, the SRS module may need replacement, and the vehicle body structure must be assessed for crash damage that affects the sensors' mounting positions.
SRS warning light illuminated: Indicates a fault in the SRS system that may affect airbag deployment in a crash. Common causes include a loose or disconnected clock spring (the rotary connector in the steering column, which carries the driver airbag circuit through the steering wheel's rotation), a disconnected airbag connector under a seat, a failed seatbelt pretensioner, or a corrupted SRS module after a minor impact (even one that did not deploy the airbags). The SRS warning light always requires professional diagnosis using SRS-specific diagnostic software — standard OBD-II readers typically cannot read SRS fault codes.
Airbag deployed after collision: After airbag deployment, the vehicle should not be driven until the SRS system has been professionally assessed and all deployed components replaced. Driving a vehicle with deployed airbags and a faulted SRS system means there is no airbag protection in a subsequent collision.
Level 1 — SRS Warning Light: The SRS warning light illuminates briefly at every ignition cycle as a system self-test and then extinguishes. A light that remains on after this self-test indicates a stored fault requiring diagnosis. Never ignore an illuminated SRS warning light — the airbags may be disabled. Have the fault diagnosed within the same week.
Level 2 — Seatbelt Condition: Inspect seatbelts for webbing damage, fraying, or cuts annually. After any collision where the seatbelts were loaded (even if the airbags did not deploy), the seatbelts should be inspected by a professional — pretensioner mechanisms fire once and must be replaced after any activation. A seatbelt that does not retract correctly, feels stiff, or shows damage should be replaced immediately.
Level 3 — Professional SRS Service Only: The SRS system is the only automotive system where all service — including simple connector inspection — should be performed only by trained professionals. Accidental airbag deployment causes severe burns and impact injuries and can be fatal. Always disconnect the battery and wait at least 30 seconds before performing any work near airbag components. Never attempt to modify, repair, or improvise any SRS component.
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