Restraints and Safety Systems: Description and Operation

Air Bag
An inflatable cloth cushion designed to deploy in certain frontal crashes. It supplements the protection offered by the seat belts by distributing the impact load more evenly over the vehicle occupant's head and torso.

Asynchronous
Performed in a nonperiodic fashion, (i.e., no defined time or interval).

(B+)
Battery voltage, (B+) The voltage available at the battery at the time of the indicated measurement. With the key "ON" and the engine not running, the system voltage will likely be between 12 and 12.5 volts. At idle the voltage may be 14 to 16 volts. The voltage could be as low as 10 volts during engine cranking.

Bulb Check
The SDM will cause the "AIR BAG" warning lamp to flash seven times and then go "OFF" whenever the ignition switch transitions to the ON position from any other ignition switch position and no malfunctions are detected.

"CONTINUOUS MONITORING"
Tests performed by the SDM on the SRS every 100 milliseconds while "Ignition 1" voltage is in the normal operating voltage range at the SDM.

Data Link Connector (DLC)
Formerly "DLC" a connector which allows communication with an external computer, such as a scan tool.

Datum Line
A base line parallel to the plane of the underbody or frame from which all vertical measurements originate.

Deploy
To inflate the air bag.

Deployment Loops
The circuits which supply current to the air bag assemblies to deploy the air bag.

Diagnostic Trouble Code (DTC)
Formerly "Code", a numerical designator used by the SDM to indicate specific SRS malfunctions.

Driver Current Source
An output of the SDM which applies current into the driver air bag assembly circuit during the "Initiator Assembly Resistance Test".

Driver Air Bag Assembly
An assembly located in the steering wheel hub consisting of an inflatable bag, an inflator and an initiator.

EEPROM
Electronically Erasable Programmable Read Only Memory. Memory which retains its contents when power is removed from the SDM.

Ignition Cycle
The voltage at the SDM "Ignition 1" inputs, with ignition switch "ON", is within the normal operating voltage range for at least ten seconds before turning ignition switch "OFF".

Ignition 1
A battery voltage (B+) circuit which is only powered with the ignition switch in the ON, or START positions.

Initiator
The electrical component inside the air bag assembly which, when sufficient current flows, sets off the chemical reaction that inflates the air bag.

"Initiator Assembly Resistance Test"
Tests performed once each ignition cycle when no malfunctions are detected during "Turn-ON" or "Continuous Monitoring." This test checks for the correct SDM configuration for the vehicle, shorts to "Ignition 1 in the deployment loops, high resistance or opens in the "Driver Side High", "Driver Side Low", "Passenger Side High" and "Passenger Side Low" circuits and measures the resistance of the inflator assembly consisting of:
1. Initiators.
2. SRS coil assembly (driver side only).
3. Connectors and associated wiring.

Normal Operating Voltage Range
The voltage measured between the SDM "Ignition 1" terminals and "Ground" terminals is between 9 and 16 volts.

Passenger Current Source
An output of the SDM which applies current into the passenger air bag assembly circuit during the "Initiator Assembly Resistance Test".

Passenger Air Bag Assembly
An assembly located in the right side of the instrument panel consisting of an inflatable bag, an inflator and an initiator.

Scan Tool
An external computer used to read diagnostic information from on-board computers via the data link connector.

SDM
Sensing and Diagnostic Module which provides reserve energy to the deployment loops, deploys the air bags when required and performs diagnostic monitoring of all SRS components.

Serial Data
Information representing the status of the SRS.

SRS
Supplemental Restraint System.

SRS Coil Assembly
An assembly of two current-carrying coils in the driver deployment loop that allows the rotation of the steering wheel while maintaining the continuous contact of the driver deployment loop to the driver air bag assembly.

SRS Wiring Harness
The wires and connectors that electrically connect the components in the SRS.

"Turn-ON"
Test which the SDM performs on the SRS once during each ignition cycle immediately after "Ignition 1" voltage is applied to the SDM and before "Continuous Monitoring".