Air Bag Control Module: Description and Operation

SENSING AND DIAGNOSTIC MODULE (SDM) AND PRETENTIONER MODULE
The Inflatable Restraint Sensing and Diagnostic and Seat Belt Pretensioner Module (SDM) performs the following functions in the SIR system:
^ Energy Reserve - The SDM maintains 28.5 Volt Loop Reserve (28.5 VLR) energy supplies to provide deployment energy for the frontal air bags. Ignition voltage can provide deployment energy if the 28.5 Volt Loop Reserves malfunction.
^ Frontal Crash Detection - The SDM monitors vehicle velocity changes to detect frontal crashes that are severe enough to warrant deployment.
^ Rear Crash Detection - The SDM monitors vehicle velocity changes to detect rear crashes that are severe enough to warrant deployment of the seat belt pretensioners.
^ Frontal 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.
^ Seat Belt Pretensioner Deployment - During a frontal or rear crash of sufficient force, the SDM will cause enough current to flow through the pretensioners to deploy the seat belt pretensioners.
^ Crash Recording - The SDM records information regarding the SIR system status during a crash.
^ Side Impact System Malfunction Monitoring - The SDM monitors a diagnostic line from each Inflatable Restraint Side Impact Sensor (SIS). Both SISs communicate the status of the Side Impact Air Bag system to the SDM.
^ 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 lamp.

The SDM connects to the SIR wiring harness using a 45-way connector. The SDM receives power whenever the ignition switch is in the ON or START positions.