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 23 Volt Loop Reserve (23 VLR) energy supplies to provide deployment energy. 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.
Air Bag Deployment : During a frontal crash of sufficient force, the SDM will cause enough current to flow through the inflator modules to deploy the 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 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 indicator.

The SDM connects to the SIR wiring harness using a 12-way connector. The SDM harness connector uses a shorting bar across certain terminals in the contact area. Removal of the SDM Connector Position Assurance (CPA) or the harness connector itself will connect the AIR BAG warning indicator to ground through the shorting bar.

The AIR BAG warning indicator will come ON steady with power applied to the SDM when either one of the following two conditions exist:

• | The SDM CPA is removed.

• | The SDM harness connector is disconnected.

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

### AIR BAG Warning Indicator

The ignition switch applies ignition voltage to the AIR BAG warning indicator. The AIR BAG warning indicator receives power whenever the ignition switch is in the ON or START positions. The Sensing and Diagnostic Module (SDM)' s internal lamp driver controls the AIR BAG Warning Indicator by providing a circuit ground. The SIR system uses the AIR BAG warning indicator to do the following:

• | Verify warning indicator and SDM operation by flashing the warning indicator seven times when the ignition switch is first turned to the ON position.

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

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

- | Deployment for conditions less severe than intended

The AIR BAG warning indicator is the key to driver notification of SIR system malfunctions. Refer to SIR Diagnostic System Check for proper warning indicator 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 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.

### 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 10.0V.
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 ON. The bulb test will also occur if the IGNITION 1 voltage exceeds 17.1 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 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.
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 Loop Continuity Test: The inflatable restraint Sensing and Diagnostic Module (SDM) performs this test in order to inspect for voltage variations in the DRIVER SIDE HIGH/LOW and the PASSENGER SIDE HIGH/LOW circuitry. The module first measures the IGNITION 1 and the 23 VLR 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.
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.
Driver Current Sink: An output of the inflatable restraint Sensing and Diagnostic Module (SDM) that supplies a low resistance path to ground for the inflatable restraint steering wheel module circuit.
Driver Current Source: An output of the inflatable restraint Sensing and Diagnostic Module (SDM) that supplies current into the inflatable restraint steering wheel module circuit.
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 8.2V with the ignition switch in ON. The IGNITION 1 input voltage must remain above 8.2V for at least 10 seconds before turning the ignition switch to OFF.
Ignition 1: A Battery Voltage circuit receiving power with the ignition in ON or START.
Inflatable Restraint I/P Module: An assembly located on the RH of the I/P 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 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: 8.2-17.1 V when measuring between the inflatable restraint Sensing and Diagnostic Module (SDM) IGNITION 1 terminal and ground.
Passenger Current Sink: An output of the inflatable restraint Sensing and Diagnostic Module (SDM) that supplies a low resistance path to ground for the inflatable restraint IP module circuit.
Passenger Current Source: An output of the inflatable restraint Sensing and Diagnostic Module (SDM) that supplies current into the inflatable restraint I/P module circuit.
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, 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 0.0-6.3 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 driver/passenger 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.
23 VLR: The 23 volt loop reserve. The energy supply that is internal to the inflatable restraint Sensing and Diagnostic Module (SDM).