For 1990-2009 cars

### Component Description

#### Inflatable Restraint Sensing and Diagnostic Module

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

• | Energy Reserve - The SDM maintains 23 Volt Loop Reserve (23 VLR) energy supplies to provide deployment energy for the frontal air bags. Ignition voltage can provide deployment energy if the 23 Volt Loop Reserves malfunction.

• | Crash Detection

- | Frontal - The SDM monitors vehicle velocity changes in order to detect frontal crashes that are severe enough to warrant deployment of the frontal air bags.

- | Side Impact - The SDM monitors vehicle velocity changes along with SIS information in order to detect side impact crashes that are severe enough to warrant deployment of the side air bags.

• | Air Bag Deployment

- | Frontal - 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.

- | Side - During a side impact crash of sufficient force, the SDM will cause enough current to flow through one of the side inflator modules to deploy that side air bag.

• | Seat Belt Pretensioner Crash Detection - The SDM monitors vehicle velocity changes in order to detect frontal crashes that are severe enough to warrant deployment of the seat belt pretensioners.

• | Seat Belt Pretensioner Deployment - During a frontal crash of sufficient force, the SDM will cause enough current to flow through the pretensioners, deploying the pretensioners.

• | Frontal and Side Crash Recording - The SDM records information regarding the SIR system status during a frontal crash or a side crash.

• | Side Impact System Malfunction Monitoring - The SDM monitors a diagnostic line from each inflatable restraint side impact sensors (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 (DTCs) 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 34-way connector.

The SDM receives power whenever the ignition switch is ON.

#### Inflatable Restraint Side Impact Sensor (SIS)

The inflatable restraint side impact sensors (SIS) are crash-sensing devices used in the detection of side impact collisions. The inflatable restraint side impact sensor (LH) is located in the LH B-pillar. The inflatable restraint side impact sensor (RH) is located in the RH B-pillar. 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 module (SDM) monitors each SIS via the interface circuit. Each SIS can communicate the status of the side impact air bag system to the SDM.

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 ON.

#### 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 ON. The inflatable restraint sensing and diagnostic module (SDM) controls the lamp by communicating with the instrument cluster over the Class 2 serial data circuit. The SIR system uses the AIR BAG warning lamp to do the following:

• | Verify proper SIR system operation by commanding the lamp OFF via serial data after seven flashes. The instrument cluster flashes the AIR BAG warning lamp seven times when the ignition switch is turned ON.

• | Warn the driver of electrical system malfunctions which could potentially affect the operation of the SIR system. These malfunctions could result in one or more of the following conditions:

- | Deployment of the frontal air bag(s) or the pretensioner(s) without a frontal crash;

- | Deployment of the side air bag(s) without a side crash;

- | Non-deplyoment of the frontal air bag(s) or the pretensioner(s) in the event of a crash;

- | Non-deployment of a side air bag in the event of a side 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 Diagnostic System Check - SIR for proper operation of the AIR BAG warning lamp.

#### 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 (SIS) 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 the inflatable restraint front side impact module (LH) connector located under the driver seat that connects to the SIR wiring harness. The shorting bar shorts across the inflatable restraint front side impact module (LH) circuit during the disconnection of the inflatable restraint front side impact module (LH) connector. The shorting of the side air bag module circuitry will help prevent unwanted deployment of the side air bag when servicing the inflatable restraint front side impact module (LH), the driver seat or other SIR system components.

There is a shorting bar on the inflatable restraint front side impact module (RH) connector located under the passenger seat that connects to the SIR wiring harness. The shorting bar shorts across the inflatable restraint front side impact module (RH) circuit during the disconnection of the inflatable restraint front side impact module (RH) connector. The shorting of the side air bag module circuitry will help prevent unwanted deployment of the side air bag when servicing the inflatable restraint front side impact module (RH), the passenger seat or other SIR system components.

#### Seat Belt Pretensioners

The seat belt 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 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 pretenasioners will deploy immediately before the frontal air bags deploy in the event of a mild-to-severe frontal collision.

#### 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 or side crashes. The air bags distribute the impact load more evenly over the occupant's head and torso in order to supplement the safety belt protection.
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. When the ignition is ON with the engine OFF, the voltage is usually 11.5-12.5 V. With the engine at idle, the voltage may be 14.0-16.0 V. During engine cranking, the voltage can be as low as 10.0 V.
Bulb Test: The instrument cluster will flash the AIR BAG warning lamp seven times when the ignition switch is turned ON. The inflatable restraint sensing and diagnostic module (SDM) then commands the instrument cluster to turn OFF the AIR BAG warning lamp through Class 2 serial data. If a SIR system malfunction is present, the SDM will command the instrument cluster to turn ON the AIR BAG warning lamp after the instrument cluster has flashed the AIR BAG warning lamp seven times.
Class 2: A serial data communication protocol.
Continuous Monitoring Test: The inflatable restraint sensing and diagnostic module (SDM) continuously monitors the SIR system during each 60 millisecond interval. The IGNITION 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.
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 the pretensioner.
Deployment Loops: The circuits that supply the current to the inflator modules for air bag or pretensioner deployment.
Deployment Loop Voltage Out Of Range Test: This test is run during power-on and continuous monitoring diagnostics. The SDM performs this test in order to inspect for a short to B+ or ground within the deployment loops. If the SDM detects a short to B+ within a deployment loop, the resistance measurement test for that deployment loop will not be run.
Deployment Loop Resistance Measurement Test: This test is run during power-on and continuous monitoring diagnostics. The SDM performs this test in order to inspect for proper deployment resistance. This test is run after the deployment loop voltage out of range test as long as a short to B+ does not exist within the deployment loop.
Diagnostic Trouble Code (DTC): An alphanumeric designator used by the inflatable restraint sensing and diagnostic module (SDM) in order to indicate specific SIR 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 input greater than 9.0 V with the ignition switch ON. The IGNITION input voltage must remain above 9.0 V for at least 10 seconds before turning the ignition switch OFF.
Ignition: A B+ circuit receiving power with the ignition ON.
Inflatable Restraint IP Module: An assembly located on the RH of the IP consisting of an inflatable air bag, an inflator, and an initiator.
Inflatable Restraint Sensing and Diagnostic Module: The SDM that provides reserve energy to the deployment loops, deploys the air bags and pretensioners when required, and performs diagnostic monitoring of all SIR system components.
Inflatable Restraint Side Impact Module: An assembly located on the outboard side of the driver and front passenger seat consisting of an inflatable air bag, an inflator, and an initiator.
Inflatable Restraint Side Impact Sensor (SIS): A sensor mounted on the lower B-pillar of the vehicle that supplies an input signal to the 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: 9.0-16.0 V when measuring between the inflatable restraint sensing and diagnostic module (SDM) IGNITION 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 voltage, and before the continuous monitoring tests.
Scan Tool: An off-board computer that reads on-board computer diagnostic information through the use of a DLC.
Serial Data: The information communicated to an off-board computer using the DLC. Some of this data represents the status of the SIR system.
SIAB: Side Impact Air Bag
SIR: Supplemental Inflatable Restraint.
SIR Wiring Harness: The wires and connectors that electrically connect the components in the SIR system.
SIS: Inflatable Restraint Side Impact Sensor