Car And Truck Airbag Operation And Description

The supplemental inflatable restraint (SIR) system supplements the protection offered by the occupant seat belt system. The SIR system has several inflator modules located throughout the vehicle, i.e. The inflatable restraint steering wheel module, inflatable restraint IP module in passenger side of dash, and the inflatable restraint side impact module - LF and RT. Each inflator module has a deployment loop that is controlled by the inflatable restraint Sensing and Diagnostic Module (SDM), which is mounted inside of the vehicle. The SDM determines the severity of a collision with the assistance of various sensor inputs.

When the SDM detects a collision of sufficient force, it will process the information provided by the sensors to further support inflator module deployment. The SDM performs continuous diagnostic monitoring of the SIR system electrical components. Upon detection of a circuit malfunction, the SDM will set a diagnostic trouble code (DTC) and inform the driver by commanding the instrument panel cluster (IPC) to turn the AIR BAG indicator ON. The steering column and knee bolsters are designed to absorb energy and compress during frontal collisions in order to limit leg movement and decrease the chance of injury to the driver and front passenger.

A frontal collision of sufficient force will deploy the frontal inflator modules. The SDM contains a sensing device (accelerometer) that converts vehicle velocity changes to an electrical signal. In some vehicles, the SDM receives a signal from the electronic frontal sensor (EFS) which can help determine the severity of some types of frontal collisions. The SDM contains a microprocessor, which performs calculations using the measured accelerations and compares these calculations to a value stored in memory.

When the generated calculations exceed the stored value, the SDM will cause current to flow through the frontal deployment loops, deploying the frontal inflator modules. Once the inflator modules are inflated, they quickly deflate through the air bag vent holes and/or the bag fabric. After the inflator modules are deployed, the SDM sets a deployment commanded DTC and then commands the IPC to turn the AIR BAG indicator ON. The SDM, IP module, steering wheel module, steering wheel module coil and the connecting wires make up the frontal deployment loops. The SDM continuously monitors the deployment loops for malfunctions and commands the IPC to turn the AIR BAG indicator ON if a fault is detected.


Does it cause the seat belts to lock-up?

-Yes, when the airbags are deployed, a small explosive charge in the seat belt buckle is activated and that tightens the seat belt around the occupant to keep them in the optimal position to be in during a crash. It is not much different than on cars without airbags, as a normal seat belt will lock up under hard deceleration as in a collision.


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