Air Bag Control Module: Description and Operation

SRS Control Unit

WARNING: DURING SERVICE PROCEDURES, BE VERY CAREFUL WHEN HANDLING A SRS CONTROL UNIT. NEVER STRIKE OR JAR THE SRS CONTROL UNIT. NEVER POWER UP THE SRS WHEN THE SRS CONTROL UNIT IS NOT RIGIDLY ATTACHED TO THE VEHICLE. ALL SRS CONTROL UNIT AND MOUNTING BRACKET FASTENERS MUST BE CAREFULLY TORQUED AND THE ARROW MUST BE POINTED TOWARD THE FRONT OF THE VEHICLE TO ENSURE PROPER OPERATION OF THE SRS. THE SRS CONTROL UNIT COULD BE ACTIVATED WHEN POWERED WHILE NOT RIGIDLY ATTACHED TO THE VEHICLE WHICH COULD CAUSE DEPLOYMENT AND RESULT IN PERSONAL INJURY.

The SRS CONTROL UNIT is designed to perform the following functions in the SRS:

1. Energy Reserve - The SRS CONTROL UNIT maintains 24-Volt Loop Reserve (24VLR) energy supply to provide deployment energy when ignition voltage is lost in a frontal crash.
2. Frontal Crash Detection - The SRS CONTROL UNIT monitors vehicle velocity changes to detect frontal crashes which are severe enough to warrant deployment.
3. Air Bag Deployment - When a frontal crash of sufficient force is detected, the SRS CONTROL UNIT will cause enough current to flow through the air bag assembly to deploy the air bag.
4. Malfunction Detection - The SRS CONTROL UNIT performs diagnostic monitoring of SRS electrical components and sets a diagnostic trouble code when a malfunction is detected.
5. Frontal Crash Recording - The SRS CONTROL UNIT records information regarding SRS status during frontal crash.
6. Malfunction Diagnosis - The SRS CONTROL UNIT displays SRS diagnostic trouble codes and system status information through the use of a scan tool.
7. Driver Notification - The SRS CONTROL UNIT warns the vehicle driver of SRS malfunctions by controlling the "Air Bag" warning lamp.




The SRS CONTROL UNIT is connected to the SRS wiring harness by a 24-pin connector. This harness connector uses a shorting clip across certain terminals in the contact area. This shorting clip connects the "AIR BAG" warning lamp to ground when the SRS CONTROL UNIT harness connector is disconnected or CPA (Connector Position Assurance) is not inserted even if completely connected. This will cause the "AIR BAG" warning lamp to come "ON" steady whenever the ignition switch is at the ON or START positions with the SRS CONTROL UNIT disconnected.