The supplemental restraint system (SRS), commonly known as the airbag system, is arguably the most important safety component in modern vehicles. It works alongside seatbelts to protect occupants during collisions.
When sensors detect a significant impact, airbags deploy in milliseconds, creating a cushion between passengers and hard surfaces. After inflation, they quickly deflate to allow movement.
This complex system requires several precisely functioning components working together. Today’s vehicles often feature multiple airbags positioned throughout the cabin to provide comprehensive protection.
See Also: Parts of a Seat Belt
Airbag Components
Several parts of a vehicle make up the airbag system. Each one of these components has a very specific role in making airbag inflation occur at just the right time.
Here are the main parts of an airbag system and an explanation of what each one does.
1) SRS Airbag Module/Control Unit
The SRS airbag module (sometimes called the airbag control unit or ACU) is the brains of the operation. This specialized computer constantly monitors input from various crash sensors throughout the vehicle.
When an impact occurs, the module processes this data in milliseconds to determine whether airbag deployment is necessary. It also runs self-diagnostic checks during vehicle startup to verify all system components are functioning properly.
If a malfunction is detected, the module triggers the airbag warning light on your dashboard. This module is separate from the main ECU (Engine Control Unit) that manages engine functions.
2) Impact Sensors
Impact sensors detect when a collision occurs and send that information to the SRS module. Modern vehicles contain multiple types of sensors strategically positioned throughout the frame:
- Frontal impact sensors detect head-on and offset collisions. These are typically mounted in the front crash zones of the vehicle.
- Side impact sensors are mounted in door panels, pillars, and side structures. They must trigger extremely quickly (typically within 10-15 milliseconds) due to the shorter distance between occupants and the impact point. These are critical because side collisions often provide much less crumple zone protection.
- Rollover sensors (in equipped vehicles) detect when the vehicle is tipping or rolling over to deploy curtain and other airbags designed for these scenarios.
These sensors measure deceleration forces and crash dynamics, allowing the system to deploy only the appropriate airbags for that specific collision type. The sensitivity of these sensors is precisely calibrated to prevent unnecessary deployment during minor impacts like hitting a pothole or curb.
3) Airbag Inflator
The airbag inflator is the component responsible for rapidly filling the airbag during a collision. When triggered by the airbag module, the inflator initiates a controlled chemical reaction that generates nitrogen gas. This gas fills the airbag in approximately 20-30 milliseconds (faster than the blink of an eye).
Modern vehicles use various types of inflators, including pyrotechnic devices or compressed gas systems, which are more stable and environmentally friendly than older sodium azide systems. Each airbag in the vehicle has its own dedicated inflator designed for that specific location and purpose.
4) Airbag
The airbag itself is a flexible fabric sack typically made from nylon or polyester materials. These fabrics are coated with heat-resistant materials to protect them during the rapid inflation process.
The airbags themselves are carefully folded and packed into specific mounting locations throughout the vehicle, such as the steering wheel, dashboard, side panels, and roof rails.
Upon deployment, they create a protective cushion that absorbs impact forces and prevents occupants from striking hard interior surfaces. After inflation, tiny vents in the airbag allow for controlled deflation to prevent rebound injuries.
See Also: Airbag Replacement Cost
5) Clock Spring
The clock spring (also called a spiral cable or clock coil spring) creates a continuous electrical connection between the steering wheel and the vehicle’s electrical system while allowing the steering wheel to rotate freely.
This flexible coiled wire harness carries electrical signals to and from the driver’s side airbag, horn, and steering wheel controls. It’s designed to maintain this connection regardless of steering wheel position.
When a clock spring fails, it often triggers the airbag warning light and may prevent proper airbag deployment. Clock springs typically need replacement if they become damaged or worn out over time.
6) Seat Occupancy Sensors
These sensors are pressure-sensitive devices installed beneath the passenger seat upholstery. They detect when someone is sitting in the passenger seat and can often determine approximate weight.
This information helps the control module make “smart” deployment decisions, such as deactivating the passenger airbag if the seat is empty or if the occupant is below a certain weight (which might indicate a child).
Most vehicles have a separate passenger airbag status indicator (often labeled “PASSENGER AIRBAG ON/OFF”) that shows whether the passenger frontal airbag is currently enabled or disabled based on the occupancy sensor readings.
These sensors are an important safety feature that helps prevent unnecessary or potentially harmful airbag deployments.
7) SRS Warning Light
The SRS warning light (sometimes called the airbag light) is typically displayed on the dashboard as an icon of a person with a deployed airbag.
When you start your vehicle, this light should illuminate briefly as the system performs a self-check, then turn off if everything is functioning correctly. If the light remains on or flashes, it indicates a problem with the airbag system that requires attention.
Common causes include sensor malfunctions, damaged wiring, or issues with the airbag module. Never ignore an illuminated SRS warning light, as it means the system may not function properly during a collision.
8) Wiring Harness
The wiring harness is a network of insulated cables that connects all components of the airbag system. These specialized wires transmit power and signals between the SRS airbag module, sensors, inflators, and other components. The airbag system wiring is typically color-coded and designed with redundancy features for reliability.
Damage to even a single wire in this network can compromise the entire system and trigger a warning light. Because of the critical safety function these wires serve, they’re often routed through protected areas of the vehicle to minimize the risk of damage during normal operation or minor collisions.
9) Backup Power Supply
The backup power supply is a critical safety feature that ensures airbag deployment even if the vehicle’s main battery is damaged or disconnected during a collision. This typically consists of a capacitor that stores enough electrical charge to deploy the airbags in an emergency.
The backup power supply activates instantly when the main power is interrupted, providing continuous protection during those crucial milliseconds after impact. This redundancy is necessary because many severe collisions can damage the vehicle’s electrical system before airbag deployment would normally occur.
10) Passenger Airbag Cutoff Switch
Some vehicles, particularly trucks and compact cars, feature a manual passenger airbag cutoff switch. This switch allows the driver to deliberately disable the front passenger airbag when a child seat is installed in the front passenger position.
In modern vehicles, this manual switch often works in conjunction with the seat occupancy sensors. While the sensors automatically disable the airbag for lightweight occupants, the manual switch provides an override option when needed.
Many newer vehicles with advanced seat occupancy sensors have eliminated the need for manual switches, as the sensors can reliably detect child seats and small occupants. However, older vehicles and some special-purpose vehicles still include this feature. Consult your owner’s manual to see how it works in your vehicle.
11) Crash Severity Sensors
Crash severity sensors work alongside impact sensors to measure the force of a collision. These sophisticated sensors help the airbag module determine not just whether to deploy airbags, but also how forcefully to deploy them.
Many modern vehicles feature multi-stage airbags that can inflate with varying levels of pressure depending on crash severity, occupant position, and seatbelt use. This “smart” deployment helps minimize the risk of airbag-related injuries while maximizing protection during severe crashes.
These sensors analyze factors like deceleration rate, impact angle, and crash pulse characteristics. It’s a lot more complex than most people think.
- 8 Causes of a Master Warning Light (And How to Turn It Off) - May 9, 2025
- 10 Parts of an Exhaust System (and Their Functions) - April 28, 2025
- 7 Causes of Drive Shaft Noise (When Accelerating or Turning) - April 24, 2025
were can i buy air bag replasement srs
what makes up an srs airbag motherboard