SIR System Component Description and 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 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 switch in the RUN position and the engine stopped, the voltage is usually 11.5-12.5 volts. With the engine at idle, the voltage may be 14.0-16.0 volts. During engine cranking, the voltage may be as low as 10.0 volts.

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 the OFF position to the RUN position. The bulb test will also occur if the Ignition Positive Voltage exceeds 17.1 volts and then returns within the normal operating voltage range. A malfunction could prevent the module from flashing the indicator.

Connector Position Assurance (CPA)
The Connector Position Assurance (CPA) is a small plastic insert that fits through the locking tabs of all the SIR system electrical connectors. The CPA ensures that the connector halves cannot vibrate apart. You must have the CPA in place in order to ensure good contact between the SIR mating terminals.

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.

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 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.

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 Positive Voltage input greater than 8.2 volts with the ignition switch in the RUN position. The Ignition Positive Voltage input voltage must remain above 8.2 volts for at least 10 seconds before turning the ignition switch to the OFF position.

Ignition 1: A B+ circuit receiving power with the ignition in the RUN position or the START position.

Inflatable Restraint Front End Discriminating Sensor: A sensor mounted on the front of the vehicle that supplies an input signal to the Inflatable Restraint Sensing and Diagnostic Module (SDM).

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 IP Module Switch: A manual two-position key switch located in the instrument panel, to the right of the steering wheel. This switch gives the vehicle operator the ability to enable or disable Inflatable Restraint IP module (Passenger Front Air Bag) deployment should the vehicle be involved in a severe frontal collision. The vehicle operator may choose to disable the Inflatable Restraint IP module if there is no occupant in the front seat, or if there is a child in a rear-facing child seat in the front seat.

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 volts when measuring between the Inflatable Restraint Sensing and Diagnostic Module (SDM) Ignition Positive Voltage 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 IP 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 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. 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 inspects 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.

Terminal Position Assurance (TPA)
The Terminal Position Assurance (TPA) insert resembles the plastic combs used in the control module connectors. The TPA keeps the terminal securely seated in the connector body. Do not remove the TPA from the connector body unless you remove a terminal for replacement.

23 VLR: The 23 volt loop reserve. The energy supply that is internal to the Inflatable Restraint Sensing and Diagnostic Module (SDM).