For 1990-2009 cars

### 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 a 23 Volt Loop Reserve (23 VLR) energy supply to provide deployment energy for the air bags. Ignition voltage can provide deployment energy if the 23 Volt Loop Reserves malfunction.

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

• | 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.

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

• | Malfunction Detection - The SDM performs diagnostic monitoring of the SIR system electrical components. Upon detection of a circuit or component malfunction, the SDM will set a DTC.

• | Malfunction Diagnosis - The SDM displays SIR DTCs and system status information through the use of a scan tool.

• | Driver Notification - The SDM notifies the vehicle driver of SIR system malfunctions by controlling the AIR BAG warning lamp in the instrument cluster via Class 2 serial data.

The SDM connects to the SIR wiring harness using the 18-way connector which provides power, ground, and all the required interfaces for frontal air bag deployment.

The SDM receives power whenever the ignition 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 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 lamp seven times when the ignition switch is first turned ON.

• | Notify the vehicle 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:

- | Non-deployment of the frontal air bags in the case of a frontal crash

- | Deployment for conditions less severe than intended

The AIR BAG warning lamp is the key to driver notification of SIR system malfunctions. Refer to A Diagnostic System Check - SIR 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 frontal 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. 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.

### 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. 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.
Battery Voltage: 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 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 Panel Cluster (IPC) will flash the air bag warning lamp indicator 7 times when the ignition switch is turned from OFF to RUN. 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 system. If a SIR system malfunction is present, the IPC flashes the warning indicator seven times and the SDM then commands the IPC to turn the warning lamp indicator ON. An IPC malfunction could prevent the IPC from flashing the indicator.
Class 2: A serial data communications protocol.
Continuous Monitoring Tests: The inflatable restraint Sensing and Diagnostic Module (SDM) continuously monitors the SIR system during each 60 millisecond interval. The Ignition Positive Voltage at the module must be within 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.
Deployment Loop Voltage Out Of Range Test: This test is run during power-on and continuous monitoring diagnostics. The inflatable restraint Sensing and Diagnostic Module (SDM) performs this test in order to inspect for a short circuit to voltage or ground within the deployment loops. If the SDM detects a short circuit to voltage within a deployment loop, the resistance measurement test for that deployment loop will be not be run.
Deployment Loop Resistance Measurement Test: This test is run during power-on and continuous monitoring diagnostics. The inflatable restraint Sensing and Diagnostic Module (SDM) performs this test in order to inspect for proper deployment loop resistance. This test is run after the voltage out of range test as long as a short to voltage 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 the Ignition Positive Voltage input greater than 9.0 V with the ignition switch in RUN. The Ignition Positive Voltage input must remain above 9.0 V for at least 10 seconds before turning the ignition switch to OFF.
Ignition Positive Voltage: A voltage circuit receiving power with the ignition switch in the RUN or START position.
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 (SDM): The SIR control module that provides reserve energy to the deployment loops, deploys the air bags 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 POSITIVE VOLTAGE terminal and ground.
Power-on Tests: 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 Positive 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.
SIR: Supplemental inflatable restraint.
SIR Wiring Harness: The wires and connectors that electrically connect the components in the SIR system.