Inflatable Restraint Sensing and Diagnostic Module (SDM)

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.
^ 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. When a frontal deployment occurs the SDM sends a message over the Serial Data Line Class 2. Upon receiving this message the Body Control Module (PZM) turns on the interior lights and unlocks all of the doors.
^ Frontal Crash Recording - The SDM records information regarding the SIR system status during a frontal crash.
^ Side Impact System Malfunction Monitoring - The SDM monitors a diagnostic line from each inflatable restraint Side Impact Sensing Module (SISM). Both SISMs 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 24-way connector.

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