Inflatable Restraint Sensing and Diagnostic Module (SDM)

The Sensing and Diagnostic Module (SDM) performs the following functions within the SIR system:
^ Energy Reserve The SDM maintains a 23-Volt Loop Reserve in order to provide deployment energy. If ignition voltage is lost during a frontal crash, the 23-volt loop reserve causes deployment of the air bags.
^ Frontal Crash Detection - The SDM monitors the changes in the vehicle's speed in order to detect frontal crashes which are severe enough to cause deployment.
^ Air Bag Deployment - If a frontal crash of sufficient force occurs, the SDM causes deployment of the air bags.
^ Frontal Crash Recording - The SDM records information regarding the SIR system status during a frontal crash.
^ Malfunction Detection - The SDM performs diagnostic monitoring of the SIR system electrical components. The SDM sets a diagnostic trouble code if the SDM detects a malfunction.
^ 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 driver of SIR system malfunctions by controlling the AIR BAG warning lamp.

The SDM connects to the SIR wiring harness using a 12-way connector. The SDM harness connector uses a shorting bar across certain terminals in the contact area. If you remove SDM Connector Position Assurance (CPA) or the harness connector, the AIR BAG warning lamp will connect to ground through the shorting bar. The AIR BAG warning lamp will illuminate with the power to the SDM if either one of the following two conditions exists:
^ You remove the SDM CPA
^ You disconnect the SDM harness connector

The SDM receives power if the ignition switch is at the ON or at the START positions.