Important: In order to prevent accidental deployment, shorting bars close in order to short the terminals when the connectors are separated.

Component Description

Inflatable Restraint Sensing and Diagnostic Module

The inflatable restraint sensing and diagnostic module (SDM) performs the following functions in the SIR system:

The SDM connects to the SIR wiring harness using a 24-way connector.

The SDM receives power whenever the ignition switch is in the ACC or ON positions.

Inflatable Restraint Side Impact Sensing (and Diagnostic) Module (SISM)

The inflatable restraint side impact sensing module (SISM) performs the following functions in the air bag system:

The SISM connects to the air bag wiring harness using a 5-way connector.

The SISM receives power whenever the ignition switch is in the ACC or ON positions. The SISM and the SDM are powered by the same fuse.

AIR BAG Warning Lamp

The AIR BAG warning lamp is in the instrument cluster (IPC). The inflatable restraint sensing and diagnostic module (SDM) communicates with the IPC using serial data communication. The SDM commands the IPC to turn the warning ON and OFF through serial data communication. The SIR system uses the AIR BAG warning lamp to do the following:

The AIR BAG warning lamp is the key to driver notification of SIR system malfunctions. Refer to 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 on the yellow 2-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 yellow 2-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 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 IP module connector that connects to the SIR wiring harness. The shorting bar shorts across the inflatable restraint IP module circuits during the disconnection of the inflatable restraint IP module connector. The shorting of the inflatable restraint IP module circuitry will help prevent unwanted deployment of the air bag when servicing the inflatable restraint IP 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 Pretensioners

The seat belt buckle pretensioner assembly consists of the following components:

When the vehicle is in a frontal crash of sufficient force, the inflatable restraint sensing and diagnostic 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.

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

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.

Definitions

Air Bag: An inflatable cloth cushion designed to deploy in certain frontal crashes and side impact crashes. The frontal air bags distribute the impact load more evenly over the occupant's head and torso in order to supplement the safety belt protection. The side impact air bags distribute a side impact load more evenly over the vehicle occupant's chest.

Asynchronous: An event that can occur at any time without a warning and without falling within a defined time period.

B+: The battery voltage available at the time of the indicated measurement. With the ignition in ON and the engine stopped, the voltage is usually 11.5-12.5 volts. With the engine at idle, the voltage may be 14.0-16.0 volts. During engine cranking, the voltage can be as low as 10.0 volts.

Bulb Test: The instrument cluster (IPC) will flash the air bag warning indicator 7 times when the ignition switch is turned from OFF to ON. The inflatable restraint sensing and diagnostic module (SDM) then commands the IPC to turn the warning indicator OFF through serial data communication. This indicates that there are no malfunctions in the SIR/side air bag/pretensioner systems. If a malfunction is present, the IPC flashes the warning indicator seven times and the SDM then commands the IPC to turn the warning indicator ON.

Continuous Monitoring Test: The inflatable restraint sensing and diagnostic module (SDM) continuously monitors the SIR system during each 100 millisecond interval. The Ignition 1 voltage at the module must be with the normal operating voltage range for the continuous monitoring to occur. These tests follow the power-on tests.

Current Sink: An output in each deployment loop of the inflatable restraint sensing and diagnostic module (SDM) that supplies a low resistance path to ground for the respective deployment loop circuit.

Current Source: An output in each deployment loop of the inflatable restraint sensing and diagnostic module (SDM) that supplies current into the respective deployment loop circuit.

Data Link Connector (DLC): The DLC electrically connects to many on-board computers and allows communication with an off-board computer such as a scan tool.

Datum Line: A base line parallel to the plane of the vehicle underbody or the frame. All vertical measurements originate from this base line.

Deploy: To inflate the air bag or actuate the seat belt pretensioner.

Deployment Loop Continuity Test: The inflatable restraint sensing and diagnostic module (SDM) performs this test in order to inspect for voltage variations in the deployment loop circuitry. The module first measures the Ignition 1 and the 23VLR in order to verify that the voltage is within specifications. The module then performs the deployment loop continuity test. Detection of a malfunction during these tests may prevent the resistance measurement test from occurring until the next ignition cycle. This test is part of the power-on tests and occurs before the continuous monitoring tests.

Deployment Loops: The circuits that supply the current to the inflator modules for air bag deployment and provide current to the seat belt pretensioners for pretensioner deployment.

Diagnostic Trouble Code (DTC): An alphanumeric designator used by the inflatable restraint sensing and diagnostic module (SDM) in order to indicate specific SIR/Side Air Bag/Pretensioner system malfunctions.

EEPROM (Electrically Erasable Programmable Read Only Memory) : Memory that does not require power to the inflatable restraint sensing and diagnostic module (SDM) in order to retain its contents.

Higher Priority Fault: Each DTC has an assigned priority based on its detectability with other DTCs present. The priority corresponds to the detectability of the malfunction only. This does not relate to the seriousness of the malfunction with respect to deployment or non deployment under any given condition.

Ignition Cycle: The operation of the ignition switch causes this cycle to occur. The inflatable restraint sensing and diagnostic module (SDM) must first sense Ignition 1 input greater than 7.8 volts with the ignition switch in ON. The Ignition 1 input voltage must remain above 7.8 volts for at least 10 seconds before turning the ignition switch to OFF.

Ignition 1: A B+ circuit receiving power with the ignition in ACC or ON.

Inflatable Restraint IP Module: An assembly located on the passenger side of the IP consisting of an inflatable air bag, an inflator, and an initiator.

Inflatable Restraint Sensing and Diagnostic Module (SDM): The SDM provides reserve energy to the deployment loops, deploys the air bags when required, and performs diagnostic monitoring of all SIR system components.

Inflatable Restraint Side Impact Inflator Modules: An assembly located on the outboard sides of the front seat backs consisting of an air bag, an inflator and an initiator.

Inflatable Restraint Side Impact Sensing (and Diagnostic) Modules (SISM): The SISMs provide reserve energy to the side impact deployment loops, and deploy their respective side air bag when required. The SISMs perform diagnostic monitoring of the side impact air bag system components and communicate the system status to the inflatable restraint sensing and diagnostic module (SDM).

Inflatable Restraint Steering Wheel Module: An assembly located in the steering wheel hub consisting of an inflatable bag, an inflator, and an initiator.

Inflatable Restraint Steering Wheel Module Coil: An assembly of two or more current carrying coils mounted within the steering column hub. The assembly allows the rotation of the steering wheel while maintaining continuous electrical circuit contact. Two of the coils provide continuous contact of the driver deployment loop to the inflatable restraint steering wheel module.

Initiator: Located in the inflator module, the initiator initiates the chemical reaction that inflates the air bag when sufficient current flows through the component.

Normal Operating Voltage Range: 7.8-18.0 volts when measuring between the inflatable restraint sensing and diagnostic module (SDM) Ignition 1 terminal and ground.

Power-on Test: Tests that the inflatable restraint sensing and diagnostic module (SDM) performs on the SIR system once per ignition cycle. These tests occur immediately after the module receives Ignition 1 voltage, and before the continuous monitoring tests.

Resistance Measurement Test : A test that the inflatable restraint sensing and diagnostic module (SDM) performs once per ignition cycle in order to measure the resistance of the deployment loops. The module first measures Ignition 1, 23VLR, and the deployment loop voltages in order to verify readings within specifications. The module then sources a constant current into the loop. The module measures the voltage drop across the loop and converts the value to a resistance value. This resistance value is within the range of 0.0-6.3 ohms. Upon the detection of an open circuit, the module aborts the tests in order to prevent the calculation of the resistances until the next ignition cycle. This test also checks for proper operation of the current sources. This test is part of the power-on tests and occurs before the continuous monitoring tests.

Scan Tool: An off-board computer that reads on-board computer diagnostic information through the use of a DLC.

Seat Belt Pretensioner: A pyrotechnic device located in the seat belt buckle consisting of a routing cable with piston, a piston tube, and a gas generator. When the seat belt pretensioner deploys, it shortens the buckle height.

Serial Data: The information communicated to an off-board computer using the DLC. Some of this data represents the status of the SIR system.

SIR: Supplemental inflatable restraint.

SIR Wiring Harness: The wires and connectors that electrically connect the components in the SIR system.

State Of Health (SOH) DTCs: Diagnostic Trouble Codes set by any module communicating on the class 2 serial data line. An SOH DTC indicates a class 2 serial data line malfunction.

23VLR: The 23 volt loop reserve. The energy supply that is internal to the inflatable restraint sensing and diagnostic module (SDM).