Frontal SIR System Description

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The frontal Supplemental Inflatable Restraint (SIR) System consists of the following components:

AIR BAG indicator located on the instrument panel cluster (IPC)
Driver and passenger knee bolsters
Inflatable restraint front end sensors (left/right)
Inflatable restraint PASSENGER AIR BAG ON/OFF indicator
Inflatable restraint Passenger Presence System (PPS)
Inflatable restraint passenger seat belt tension sensor
Inflatable restraint seat position sensor (SPS) (left)
Inflatable restraint sensing and diagnostic module (SDM)
Inflatable restraint steering wheel module
Inflatable restraint steering wheel module coil
Inflatable restraint wiring harnesses
Seat belt pretensioners (left/right)
Steering wheel and column

A frontal collision of sufficient force will deploy the frontal air bags. The SDM contains a sensing device that converts vehicle velocity changes to an electrical signal. In the event of a frontal collision, the SDM receives a signal from the front end sensors which assists the SDM in determining the severity of some frontal collisions. The SDM contains a microprocessor that performs calculations using the measured accelerations. The SDM 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 air bags. Once the air bags are inflated they quickly deflate through the air bag vent holes. After the air bags have deployed, the SDM sets a diagnostic trouble code (DTC) and requests the IPC to turn the AIR BAG indicator ON. The SDM, instrument panel (I/P) module, steering wheel module, steering wheel module coil and the connecting wires makeup the frontal deployment loops. The SDM continuously monitors the deployment loops for malfunctions and requests the IPC to turn the AIR BAG indicator ON if a fault is detected.