Airbag System Overview

An airbag is a fabric cushion that inflates in roughly 30 milliseconds during a crash. That is faster than a blink. The entire system exists for one purpose: slow down your body's forward motion so you hit a soft bag instead of a hard steering wheel or dashboard.

Crash sensors detect rapid deceleration. Think of it this way: the car goes from 30 mph to zero almost instantly. The sensors measure that sudden stop and send a signal to the Airbag Control Module. Most vehicles have multiple crash sensors — front impact sensors in the bumper area, side impact sensors in the doors or B-pillars, and sometimes a rear sensor. Each one monitors a different direction of impact.

The ACM is the brain of the system. It receives signals from every crash sensor, decides which airbags need to deploy based on impact direction and severity, and fires the inflators. It also monitors every circuit in the system constantly. If it detects an open or short circuit in any airbag or sensor, it sets a code and turns on the airbag warning light. The ACM stores crash event data — after a deployment, many manufacturers require ACM replacement because the module records a permanent crash event flag.

The driver airbag sits in the steering wheel, and that wheel turns. So how does the electrical connection stay intact? A clockspring. It is a flat ribbon cable coiled inside a housing mounted on the steering column behind the wheel. As you turn the steering wheel, the ribbon cable winds and unwinds — maintaining a continuous electrical path to the driver airbag, horn, and steering wheel controls. Think of it like a tape measure that rolls in and out as the wheel turns. If the clockspring breaks, you lose the connection to the driver airbag and the warning light comes on.

Inside each airbag module is an inflator — a small canister containing a chemical propellant, usually sodium azide. When the ACM sends a firing signal, an electrical igniter sets off the propellant. The chemical reaction produces nitrogen gas almost instantly, which inflates the fabric bag. Vent holes in the bag let the gas escape after initial inflation so the bag deflates as your body contacts it. This controlled deflation is what absorbs your energy. The bag does not stay rigid — it is designed to cushion and collapse. After deployment, the inflator is spent and the entire module must be replaced.