Air Bag Control Module: Description and Operation

PURPOSE
The control module processes input from the front impact sensors and integrated safing sensor, supplies power to ignite the gas generators of the airbag module and pyrotechnic seatbelt tensioner and constantly performs defect monitoring.

OPERATION
Standby Mode
For all ignition key positions except "Off", the Supplemental Restraint System (SRS) is in standby mode, and the control module constantly verifies that the system is functioning and ready to operate if necessary. After the ignition is switched "On", the SRS warning lamp should light up and go out after a six-second test verifying that the system is in standby mode.

Power
The electric power for the system, which is required for the igniting and monitoring electronics, is taken from the vehicle battery. In the event of battery failure or power loss due to accident, power for ignition is supplied by a capacitor within the control module.

To assure positive ground contact, the diagnostic module unit has its own central ground connection. No other connections must be made to this ground connection.

Deployment
To avoid unwarranted airbag inflation under normal driving conditions at least two sensors, one of which must always be the safing sensor (within the control module), must be activated simultaneously. When this occurs, the control module discharges the internal capacitor causing ignition of the gas generators, filling the airbag and tightening the pyrotechnic seatbelt tensioner.

Defect Detection
The control module constantly monitors the system for defects. Recognized defects are stored in defect memory and the driver alerted via the SRS lamp. A series of coded flashes from the indicator lamp will inform the technician as to what the problem is.

A fault is indicated if the SRS lamp:
- Does not come "On" when the ignition is switched "On".

- Lamp only goes "Out" for a brief period after the 6 second test and then comes "On" again or flashes.

- Lamp comes "On" or flashes suddenly when driving.