Component Descriptions

The inflatable restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) performs the following functions in the SIR system:

Energy Reserve
The SDM maintains 28.5 Volt Loop Reserve (28.5 VLR) energy supplies to provide deployment energy for the frontal air bags. Ignition voltage can provide deployment energy if the 28.5 Volt Loop Reserves malfunction.

Frontal Crash Detection
The SDM monitors vehicle velocity changes to detect frontal crashes that are severe enough to warrant deployment.

Rear Crash Detection
The SDM monitors vehicle velocity changes to detect rear crashes that are severe enough to warrant deployment of the seat belt pretensioners.

Frontal Air Bag Deployment
During a frontal crash of sufficient force, the SDM will cause enough current to flow through the frontal inflator modules to deploy the frontal air bags.

Seat Belt Pretensioner Deployment
During a frontal or rear crash of sufficient force, the SDM will cause enough current to flow through the pretensioners to deploy the seat belt pretensioners.

Crash Recording
The SDM records information regarding the SIR system status during a crash.

Side Impact System Malfunction Monitoring
The SDM monitors a diagnostic line from each inflatable restraint Side Impact Sensor (SIS). Both SISs communicate the status of the side impact air bag system to the SDM.

Malfunction Detection
The SDM performs diagnostic monitoring of the SIR system electrical components. Upon detection of a circuit malfunction, the SDM will set a Diagnostic Trouble Code (DTC).

Malfunction Diagnosis
The SDM displays SIR Diagnostic Trouble Codes and system status information through the use of a scan tool.

Driver Notification
The SDM warns the vehicle driver of SIR system malfunctions by controlling the AIR BAG warning lamp. The SDM connects to the SIR wiring harness using a 45-way connector. The SDM receives power whenever the ignition switch is in the ON or START positions.

Inflatable Restraint Side Impact Sensor (SIS)
The inflatable restraint Side Impact Sensors (SIS) are pressure-sensitive devices used in the detection of side impact collisions. The inflatable restraint Side Impact Sensor (LH) is located in the LH front door. The inflatable restraint Side Impact Sensor (RH) is located in the RH front door. The inflatable restraint Side Impact Sensors are used to perform the following functions

Side Impact Crash Detection
Each SIS monitors vehicle velocity changes to detect side impact crashes that are severe enough to warrant deployment.

Side Air Bag System Status Communication
The inflatable restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) monitors a diagnostic line from each SIS. Both SISs communicate the status of the side impact air bag system to the SDM over these diagnostic lines. The SIS connects to the air bag wiring harness using a 2-way connector. The SIS receives power via the SDM whenever the ignition switch is in the ON or START positions.

Air Bag Warning Lamp
The AIR BAG warning lamp is represented by an icon graphic. Ignition voltage is applied to the AIR BAG warning lamp when the ignition switch is turned to the ON or START positions. The inflatable restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) controls the lamp by providing ground to the lamp driver circuit. The SIR system uses the AIR BAG warning lamp to do the following:
^ Verify the lamp operation by flashing the lamp seven times when the ignition switch is first turned to the ON position.
^ When lit, alerts the driver of electrical system malfunctions that could affect the operation of the SIR system. Certain malfunctions can result in;
- Deployment of an air bag(s) or a pretensioner(s) without a crash;
- Non-deployment of an air bag(s) or a pretensioner(s) in the event of a crash; or
- Deployment of an air bag(s) or a pretensioner(s) for conditions less severe than intended.
The AIR BAG warning lamp is the key to driver notification of SIR system malfunctions. Refer to the SIR Diagnostic System Check for proper lamp operation.

Inflatable Restraint Steering Wheel Module Coil
The inflatable restraint steering wheel module coil consists of two or more current-carrying coils. The inflatable restraint steering wheel module coil attaches to the steering column. Two of the current-carrying coils allow rotation of the steering wheel while maintaining continuous contact of the driver deployment loop to the inflatable restraint steering wheel module.

There is a shorting bar across pins 7 and 8 on the 8-way connector near the base of the steering column that connects the inflatable restraint steering wheel module coil to the SIR wiring harness. The shorting bar shorts the circuits to the inflatable restraint steering wheel module coil and inflatable restraint steering wheel module during the disconnection of the 8-way connector. The shorting of the inflatable restraint steering wheel module coil and inflatable restraint steering wheel module circuitry will help prevent unwanted deployment of the air bag when servicing the steering column or other SIR system components.

Inflator Modules
The inflator modules consist of an inflatable bag and an inflator. An inflator consists of a canister of gas-generating material and an initiating device. The initiator is part of the deployment loop. When the vehicle is in a frontal crash of sufficient force, the inflatable restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) causes current to flow through the frontal air bag deployment loops. When the vehicle is in a side impact crash of sufficient force, the inflatable restraint Side Impact Sensing Module (SISM) causes current to flow through the side impact air bag deployment loops. Current passing through the initiator ignites the material in the inflator module. The gas produced from this reaction rapidly inflates the air bag.

There is a shorting bar on the inflatable restraint steering wheel module side of the upper steering column connector that connects the inflatable restraint steering wheel module coil to the inflatable restraint steering wheel module. The shorting bar shorts across the inflatable restraint steering wheel module circuits during the disconnection of the upper steering column connector. The shorting of the inflatable restraint steering wheel module circuitry will help prevent unwanted deployment of the air bag when servicing the inflatable restraint steering wheel module, the steering column or other SIR system components.

There is a shorting bar on the inflatable restraint I/P module connector that connects to the SIR wiring harness. The shorting bar shorts across the inflatable restraint I/P module circuits during the disconnection of the inflatable restraint I/P module connector. The shorting of the inflatable restraint I/P module circuitry will help prevent unwanted deployment of the air bag when servicing the inflatable restraint I/P module, the instrument panel or other SIR system components.

There is a shorting bar on each inflatable restraint side air bag module connector that connects to the SIR wiring harness. The shorting bar shorts across the inflatable restraint side air bag module circuits during the disconnection of the inflatable restraint side air bag module connector. The shorting of the inflatable restraint side air bag module circuitry will help prevent unwanted deployment of the air bag when servicing the inflatable restraint side air bag module, the seat or other SIR system components.

Seat Belt Side Buckle Pretensioners
The seat belt side buckle pretensioner assembly consists of the following components:
^ An end release buckle
^ A buckle sleeve
^ A routing cable with piston
^ A piston tube
^ A mounting bracket
^ A gas generator

When the vehicle is in a frontal crash of sufficient force, the inflatable restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) causes current to flow through the frontal air bag deployment loops and the pretensioner deployment loops. Current passing through the initiator ignites the material in the pretensioner gas generator. The gas produced from this reaction rapidly shortens the seat belt buckle height. The seat belt side buckle pretensioners will deploy in the event of a mild frontal collision (pretensioner-only deployment). They will deploy immediately before the frontal air bags deploy in the event of a mild-to-severe frontal collision (air bag and pretensioner deployment).

Steering Column
The steering column is energy absorbing. The steering column can compress during a frontal crash in order to decrease the chance of injury to the driver.

Knee Bolster
The knee bolsters absorb energy and control the forward movement of the vehicle's front seat occupants during a frontal crash, by limiting leg movement.