What Is SRS? – Supplemental Restraint System Explained
SRS (Supplemental Restraint System) is the vehicle safety system responsible for controlling airbags and other restraint components during a collision. The system works together with seat belts to reduce injuries by detecting crashes and activating protection devices when necessary.
The SRS system does not replace the seat belt. It works as an additional safety system that provides extra protection during severe impacts.
SRS System Components
- ACM (Airbag Control Module): The main computer that processes crash information and controls deployment.
- Impact Sensors: Detect sudden acceleration changes caused by collisions.
- Airbags: Driver, passenger, side, curtain, and knee airbags depending on vehicle design.
- Seat Belt Pretensioners: Tighten seat belts during a crash.
- Clock Spring: Provides electrical connection between steering wheel controls and the airbag.
- OCS (Occupant Classification System): Detects passenger presence and weight.
How Does SRS Work?
During normal operation, the Airbag Control Module continuously monitors sensor signals and system circuits. When a collision occurs, the module analyzes:
- Impact direction.
- Crash severity.
- Vehicle acceleration changes.
- Occupant information.
If the conditions meet the deployment requirements, the module activates airbags and pretensioners within milliseconds.
Typical SRS Signal Flow Diagram
SRS Diagnostic Procedure
- Connect an SRS-compatible diagnostic scanner.
- Read stored DTC codes from the Airbag Module.
- Check freeze frame information if available.
- Inspect wiring connectors and sensors.
- Use live data to verify sensor communication.
- Repair the fault and clear codes.
- Perform system verification.
Live Data Diagnosis (Advanced Scan Tool)
Professional scan tools allow technicians to view real-time SRS information and determine whether a problem is caused by a sensor, wiring, or control module.
How To Enter Live Data
- Connect the scanner to the DLC connector.
- Select vehicle make, model, and year.
- Enter:
System → SRS Airbag → Data Stream / Live Data
Important Live Data Parameters
- Impact Sensor Status: Shows sensor recognition and condition.
- Communication Status: Confirms module communication.
- Battery Voltage: Checks power supply stability.
- Crash Data: Shows stored collision information.
- Occupant Detection Status: Monitors passenger classification.
Advanced Scanner Functions
- Read and clear SRS trouble codes.
- View freeze frame data.
- Record live data graphs.
- Compare sensor status.
- Perform calibration procedures when supported.
Common SRS Fault Causes
- Damaged impact sensor.
- Broken wiring.
- Corroded connectors.
- Low battery voltage.
- Previous accident repairs.
- Faulty SRS module.
Important Safety Note
SRS circuits require special safety procedures. Never test airbag wiring using a test light or apply external voltage. Always follow manufacturer repair instructions.
Related SRS Terms
- ACM – Airbag Control Module
- Impact Sensor
- LFIS / RFIS
- SIS – Side Impact Sensor
- OCS – Occupant Classification System
- Seat Belt Pretensioner
Related DTCs
SRS-related codes can vary by manufacturer. See available Airbag DTC articles in the OBDSpark SRS section.
OBDSpark Technician Tip: A good diagnosis starts with understanding the complete SRS system, not only replacing parts after a fault code appears.