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.

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

• | 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 crash of sufficient force, the SDM will cause enough current to flow through the pretensioners to deploy the seat belt pretensioners.

• | Frontal Crash Recording - The SDM records information regarding the SIR system status during a frontal 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.

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

• | 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 RUN or START positions.

#### 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 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 RUN 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 RUN or START positions. The inflatable restraint sensing and diagnostic 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 RUN 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 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 Buckle Side Belt 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 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. With the ignition in RUN and the engine stopped, the voltage is usually 11.5 -12.5V. With the engine at idle, the voltage may be 14.0 -16.0 V. During engine cranking, the voltage can be as low as 10.0V.
Bulb Test: The inflatable restraint sensing and diagnostic module (SDM) will cause the air bag warning indicator to flash 7 times. Under normal operation, this occurs when the ignition is turned from OFF to RUN. The bulb test will also occur if the IGNITION voltage exceeds 16.0 V and then returns within the normal operating voltage range. A malfunction could prevent the module from flashing the indicator.
Continuous Monitoring Test: The inflatable restraint sensing and diagnostic module (SDM) continuously monitors the SIR system during each 100 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.
Deployment Loops: The circuits that supply the current to the inflator modules for air bag deployment.
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 in RUN. The IGNITION input voltage must remain above 9.0 V for at least 10 seconds before turning the ignition switch to OFF.
Ignition: A B+ circuit receiving power with the ignition in RUN or START.
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 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.
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 six deployment loops. The SDM first measures IGNITION, 23 VLR, 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 - 6.6 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 six deployment loop 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.
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.
VLR: The 23 Volt loop reserve. The energy supply that is internal to the inflatable restraint sensing and diagnostic module (SDM). The 23 VLR provides deployment energy for the frontal air bags only.