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 RUN or START positions.

AIR BAG Warning Lamp

The AIR BAG warning lamp is in the instrument panel 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 perform the following functions:

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 2 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. The shorting bar 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 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. The shorting bar 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. The shorting bar 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 may 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 in order to deploy in certain frontal 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.

Asynchronous: An event that may 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 11.5V to 12.5V. With the engine at idle, the voltage may be 14.0V to 16.0V. During engine cranking, the voltage may be as low as 10.0V.

Bulb Test: The instrument panel cluster (IPC) will flash the air bag warning 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 malfunction is present, the IPC flashes the warning indicator 7 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 positive 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.

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 positive voltage 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.

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 the 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 positive voltage greater than 7.8V with the ignition switch in the RUN position. The ignition positive voltage must remain above 7.8V for at least 10 seconds before turning the ignition switch to the OFF position.

Ignition Positive Voltage: A B+ circuit receiving power with the ignition in RUN or START (previously called ignition positive voltage).

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

Inflatable Restraint Sensing and Diagnostic Module: 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 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 2 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: 7.8V to 18.0V when measuring between the inflatable restraint sensing and diagnostic module (SDM) ignition positive voltage 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 positive 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 positive voltage, 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. 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 inspects 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.

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 Data Line. An SOH DTC indicates a Class 2 Data Line malfunction.

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