Am I Safe if My Airbag Warning Light Is On?
With roots dating as far back as 1951, the modern airbag system is one of the greatest innovations in automobile safety ever invented. Unfortunately, whenever your airbag warning light or supplemental inflatable restraint (SIR) warning lamp is illuminated, this life-saving measure is most likely deactivated. This leaves you and your passengers in danger of being thrown into the steering wheel, dash, windshield or support pillars if there’s a collision.
So why is the airbag warning light illuminated? More importantly, what can you do to have it repaired? To answer these questions we must first gain a basic knowledge of SIR systems and their components.
How Does an Airbag Work?
When a vehicle is involved in an accident, various impact sensors are activated. The impact sensors determine the angle and severity of the crash. They transmit a signal to the airbag control module. This control module take this data and other inputs like vehicle speed, transmission shifter position and engine load. It determines in a split-second if the airbag(s) should be deployed.
If the control module determines the airbag(s) should be deployed, it sends a voltage signal to the airbag module igniter. The igniter reacts in conjunction with a pyrotechnic device to create a controlled explosion inside the airbag. When the explosion occurs, compressed air, carbon dioxide, or nitrogen releases inside the airbag. This inflates it and forms a durable protective pillow between the inner walls of the vehicle and the passengers. Once the airbag inflates, it immediately begins to deflate, removing the risk of suffocation (or other injury) to vehicle occupants.
In addition to crash protection, the SIR control module also performs self-tests and constantly monitors airbag module and airbag sensor wiring circuits when the ignition is on. If the SIR control module detects irregularities in any of the monitored circuits, a code is stored and an airbag warning lamp will illuminate. When the SIR system stores a code, it typically disables airbag deployment until the malfunction is repaired.
Key Components of the SIR System
There are six key components to the SIR system. Each component is critical to keeping you safe in the event of an accident. You want to be sure you and your passengers are protected if there’s a collision. If your airbag light comes on, make an appointment to determine which of the following may be the issue.
SIR Control Module
The SIR control module may be a stand alone unit but is more often than not integrated into the powertrain control module (PCM) or body control module (BCM). It is responsible for monitoring and control of the SIR system, including airbag warning lamp illumination. While the SIR control module rarely fails, it may be affected by blown fuses, burnt fusible links, bad relays, and reprogramming errors.
Repair Tip: When testing system fuses, we make sure the circuit is loaded. Fuses in an unloaded circuit may appear normal even when blown.
Airbag Warning Light
The amber airbag warning lamp is located in the instrument panel of the dash. When a SIR system code is stored, the SIR controller activates the SIR warning lamp (a.k.a. airbag warning light). SIR warning lamp circuitry is also regularly monitored by the SIR control module. In all likelihood, crash protection will disable when the SIR warning lamp illuminates.
Repair Tip: When a SIR warning lamp code is stored, we know to check and see if the amber lamp is on with the ignition key on and the engine off. If it is not, we usually suspect that the bulb is defective.
Driver Airbag Module
Most often called “the airbag” this is the business end of the SIR system. It is usually situated on the steering wheel in the horn pad and consists of an airbag, a propellant charge, and a pressure regulator. In some cases a temperature sensor may also be integrated into this unit.
Repair tip: We know that an illuminated airbag warning lamp accompanied by an inoperative horn, usually points to a defective clock spring (underneath the steering wheel).
Passenger Airbag Module
The passenger airbag module functions in much the same manner as the driver airbag module but is located near the glove box in the passenger side dash. One key difference is the passenger weight sensor in the passenger seat. This sensor prevents deployment of the passenger airbag when a small or lightweight person (that may be injured by the porous airbag) is in the seat. The SIR control module monitors airbag regulator and igniter resistance levels constantly. A SIR code will be stored and an airbag warning lamp illuminates if a discrepancy is detected in any of the airbag module circuits.
Side Curtain Airbag Module
The side curtain airbag deploys from the door inward in the event of a motor vehicle crash. The air-filled nylon bag prevents the driver and passengers from slamming into doors and door pillars in a crash. Unlike frontal impact airbags, side impact airbags may use CO2 cartridges for inflation purposes. Other types of airbags include seat-mounted side impact, knee bolster, and inflatable seat-belts.
Impact Sensors
Front right and front left impact sensors are responsible for crash detection. They also determine the crash angle, type, and severity. In addition to front impact sensors, there are also side impact sensors and rollover sensors. The SIR control module monitors sensor resistance and voltage and stores a code if input data is outside specified parameters. You should replace impact sensors that have been deployed.
If you see your airbag light come on, you want to make sure that you bring it to a professional right away. Even though you can drive while it is illuminated, there is no guarantee that the airbag will deploy if you get into an accident. Make an appointment or just drop by and let the SIR experts at Hong Kong Auto Service help with your airbag woes. The life you save might just be your own!