Airbag System (SRS)

The Supplemental Restraint System (SRS) is the vehicle's primary passive occupant protection system, consisting of airbag modules, crash sensors, a central SRS control module, seat belt pretensioners, and the wiring network connecting them. A modern passenger vehicle contains 6–10 or more airbag modules: frontal driver and passenger bags, side curtain bags protecting the entire window line, seat-mounted thorax bags, and on some designs knee bags, rear curtain bags, and pedestrian bonnet airbags. The SRS control module monitors deceleration inputs from crash sensors 1,000 times per second and determines within 10–30 milliseconds of a collision whether a deployment threshold has been met. When the threshold is met, the module sends a firing signal to the relevant airbag inflators — which use a pyrotechnic charge to generate nitrogen gas and inflate the bag in 20–30 milliseconds, creating a cushion between the occupant and the vehicle interior surfaces before the occupant's body moves forward.

The SRS system reduces severe and fatal occupant injuries in frontal, side, and rollover collisions by decelerating the occupant over a longer time interval than would occur with direct contact with the steering wheel, dashboard, or door structure. The airbag itself is not a cushion in the traditional sense — it inflates and immediately begins deflating through vent holes as the occupant's body contacts it, controlling the deceleration rate and distributing the contact force over a larger body surface area. The seat belt pretensioner fires simultaneously with the frontal airbags, removing slack from the belt and holding the occupant firmly against the seat before the bag deploys, ensuring the occupant is in the correct position to interact with the bag. Without correct seatbelt use, an airbag deployment can cause severe injury rather than preventing it — the SRS is supplemental, not a replacement for the primary restraint of the seatbelt.

SRS warning light illuminated on the dashboard: A fault has been detected in the SRS circuit. The entire SRS system may be disabled until the fault is cleared — meaning no airbags will deploy in a collision. Read the fault code immediately; common causes include a seat sensor connection issue, a clock spring fault, a disconnected component under a seat, or a water-damaged SRS module.

SRS light illuminated after a minor collision without airbag deployment: The crash sensor may have registered an event that did not meet deployment threshold but has recorded a fault code or set a soft code. Some SRS components may require replacement even without deployment — have the system scanned and cleared by a qualified technician who can confirm which codes are stored and whether component replacement is required.

Airbags deployed after a collision — vehicle appears driveable: The vehicle must not be driven after any airbag deployment. Deployed airbags and their ignitors are single-use. All deployed modules, the SRS control module, seat belt pretensioners (which also fire during deployment), and any wiring damage must be replaced by a specialist before the vehicle is returned to service.

Level 1 — Owner check: The SRS warning light should illuminate briefly at every start-up (system self-test) and extinguish. An SRS light that remains on during driving means airbag protection may be compromised. Do not place objects on the dashboard or front seats that could interfere with airbag deployment paths. Do not modify steering wheels, seat covers, or dashboard components without confirming compatibility with SRS components.

Level 2 — Detection: Confirm SRS fault code origin before purchasing replacement parts — the most common non-crash SRS fault is a disconnected seat occupancy sensor connector under the seat (moved during cleaning) or a clock spring (spiral cable) fault. Reconnecting the connector or replacing the clock spring resolves many SRS faults without module or airbag replacement.

Level 3 — Professional service: Any SRS work requires airbag circuit deactivation before disassembly (battery disconnected and system bleed-down time observed — typically 2–10 minutes per manufacturer specification). Working on live SRS circuits risks accidental airbag deployment causing serious injury. SRS module replacement requires VIN coding and may require deployment data clearing if a collision event is stored.