Air Bag Control Module: Description and Operation

Description:

CAUTION: Be careful when you handle a Sensing and 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 inflatable restraint sensing and diagnostic module (SDM) performs the following functions in the SIR system.
^ Energy Reserve - The inflatable restraint sensing and diagnostic module 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 inflatable restraint sensing and diagnostic module monitors vehicle velocity changes to detect frontal crashes that are severe enough to warrant deployment.
^ Air Bag Deployment - During a frontal crash of sufficient force, the inflatable restraint sensing and diagnostic module will cause enough current to flow through the inflator modules to deploy the air bags.
^ Frontal Crash Recording - The inflatable restraint sensing and diagnostic module records information regarding the SIR system status during a frontal crash.
^ Malfunction Detection - The inflatable restraint sensing and diagnostic module performs diagnostic monitoring of the SIR system electrical components. Upon detection of a circuit malfunction, the inflatable restraint sensing and diagnostic module will set a diagnostic trouble code.
^ Malfunction Diagnosis - The inflatable restraint sensing and diagnostic module displays SIR diagnostic trouble codes and system status information through the use of a scan tool.
^ Driver Notification - The inflatable restraint sensing and diagnostic module warns the vehicle driver of SIR system malfunctions by controlling the AIR BAG warning lamp.

The inflatable restraint sensing and diagnostic module connects to the SIR wiring harness using a 12-way connector. The inflatable restraint sensing and diagnostic module harness connector uses a shorting bar across certain terminals in the contact area. Removal of the inflatable restraint sensing and diagnostic module Connector Position Assurance (CPA) or the harness connector itself will connect the AIR BAG warning lamp to ground through the shorting bar.