Air Bag Control Module: Description and Operation

Diagnostic Monitor
The diagnostic monitor contains a microprocessor that monitors the electrical system components and connections. The monitor performs a self-check of the microprocessor internal circuits and energizes the system readiness indicator during prove out and whenever a fault occurs. System electrical faults can be detected and translated into coded warning indicator displays. If certain faults occur, the microprocessor will disable the system by opening a thermal fuse built into the monitor. If a system fault exists and the warning indicator is malfunctioning, an audible tone will be heard indicating the need for service.

An air bag system backup power supply is included in the diagnostic monitor to provide air bag deployment power if the battery or battery cables are damaged in an accident before the crash sensors close. The power supply will deplete its stored energy approximately one minute after the positive cable of the battery is disconnected.

WARNING: THE BACKUP POWER SUPPLY ENERGY MUST BE DEPLETED BEFORE ANY AIR BAG COMPONENT SERVICE IS PERFORMED. TO DEPLETE THE BACKUP POWER SUPPLY ENERGY, DISCONNECT THE POSITIVE BATTERY CABLE AND WAIT ONE MINUTE.

System Readiness Indicator
The system readiness indicator will light continuously for approximately six seconds whenever the ignition switch is turned from OFF to RUN if the air bag is working properly. If an air bag system fault is present, the indicator will either fail to light, remain lit continuously or light in a flashing manner. The flashing manner may not occur until approximately 30 seconds after the ignition switch has been turned from OFF to RUN. This is the time required for the diagnostic monitor to test and verify any and all system faults. If the air bag indicator is inoperative and an air bag system fault exists, a tone will sound signaling that the air bag readiness indicator is inoperative and an air bag system fault exists.

Tone Generator
The air bag readiness indicator is the prime means of determining the air bag system condition. However, a series of five sets of five tones will be heard if the readiness indicator is out and a fault occurs in the system. This also means that the Supplemental Air Bag System is in need of service. The tone pattern will repeat periodically until the fault and indicator are serviced. Unless serviced, the Supplemental Air Bag Restraint System may not function properly in the event of an accident.