Air Bag Control Module: Description and Operation

CAUTION: Be careful when you handle a Sensing & Diagnostic Module (SDM). Do not strike or jolt the SDM. Before applying power to the SDM:
^ Remove any dirt, grease, etc. from the mounting surface.
^ Position the SDM horizontally on the mounting surface.
^ Point the arrow on the SDM toward the front of the vehicle.
^ Tighten all of the SDM fasteners and SDM bracket fasteners to the specified torque value.
Failure to follow the correct procedure could cause air bag deployment, personal injury, or unnecessary SIR system repairs.

The Sensing and Diagnostic Module (SDM) performs the following functions in the SIR system.
^ Energy Reserve - The SDM maintains a 23 Volt Loop Reserve (23 VLR) energy supplies to provide deployment energy. If ignition voltage is lost during a frontal crash, the 23 VLR supplies will deploy the air bags.
^ Frontal Crash Detection - The SDM monitors vehicle velocity changes to detect frontal crashes which are severe enough to warrant deployment.
^ Air Bag Deployment - When a frontal crash of sufficient force is detected, the SDM will cause enough current to flow through the inflator modules to deploy 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 and sets a diagnostic trouble code when a malfunction is detected.
^ 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 12-way connector. The SDM harness connector uses a shorting bar across certain terminals in the contact area. Removal of the SDM Connector Position Assurance (CPA) or the harness connector itself will connect the AIR BAG warning lamp to ground through the shorting bar.

The AIR BAG warning lamp will come ON steady with the power applied to the SDM when either one of the following two conditions exist:
^ You remove the SDM CPA.
^ You disconnect the SDM harness connector.

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