Air Bag Control Module (ACM)

ACM contains a microprocessor, an impact sensor and an energy storage capacitor. The microprocessor contains air bag system logic. Air bag system logic includes On-Board Diagnostics (OBD) capability. ACM communicates with other modules via the Programmable Communication Interface (PCI) bus circuit.

ACM microprocessor monitors impact sensor signal and air bag system electrical circuits to determine system readiness. If ACM detects a monitored system fault, a message is sent via PCI bus circuit to Mechanical Instrument Panel (MIC) module to turn air bag indicator light on. ACM is preprogrammed to determine when deceleration rate signaled by impact sensor indicates an impact severe enough to require air bag system protection. When preprogrammed conditions are met, ACM sends a signal to deploy air bag system components.

The impact sensor is an accelerometer that senses the rate of vehicle deceleration, which provides verification of direction and severity of an impact. Impact sensor is calibrated for specific vehicle, and is only serviced as an integral part of ACM. ACM energy storage capacitor provides air bag system protection in severe secondary impact if initial impact has damaged or disconnected vehicle battery, but initial impact is not severe enough to deploy air bags.

MIC module performs air bag indicator light check when ignition switch is turned to RUN or START position. MIC module turns indicator light on for 6-8 seconds. Light turns off if ACM determines no system malfunctions exist. Light remains on if ACM determines an air bag system malfunction or if MIC light circuit short to ground exists. If light turns on for longer than 8 seconds and then goes off, an intermittent problem in air bag system is indicated. For additional information on air bag system, see AIR BAG RESTRAINT SYSTEMS - CARS article.