Air Bag System

Supplemental Restraint System (SRS), or air bag system, is designed to deploy air bags in a frontal or lateral (side) impact of moderate to severe force. SRS consists of an AIR BAG warning lamp, driver air bag module, passenger air bag module, passenger air bag on-off switch, driver and passenger seat belt pretensioners, clockspring and Air Bag Control Module (ACM). In addition, some models may be equipped with right and left curtain (head impact) air bag modules and Side Impact Air Bag Control Modules (SIACM). The system is most effective when used in conjunction with the seat belt system.

The ACM is an electronic module that monitors the air bag system for proper operation, stores DTCs, and controls the AIR BAG warning lamp and chime. The ACM contains the sensor and actuator that is responsible for air bag deployment. There are no external impact sensors. The ACM provides diagnostic information to the technician through the DRBIII(R) through the PCI Bus. Some circuits are tested continuously; others are checked only under certain circumstances. The warning lamp and chime are driven with messages relayed to the Instrument Cluster and CTM from the ACM through the PCI Bus. Also, ACM monitors status of passenger air bag on-off switch. ACM will not deploy passenger air bag module when passenger air bag on-off switch is in OFF position.

The AIR BAG warning lamp is the only point at which symptoms of a system malfunction can be observed by the customer. Whenever the ignition switch is turned to the RUN or START position, the ACM performs a bulb check by turning the AIR BAG warning lamp on for 6-8 seconds. If the lamp turns off after 6-8 seconds, it means that the ACM has checked the system and found it to be free of discernible malfunctions. If the lamp remains on, there could be an active fault in the system or the circuit that operates the lamp may be shorted to ground. If the lamp comes on and stays on for a period longer than 6-8 seconds, then goes off, there is usually an intermittent problem in the system.

The ACM has its own set of DTCs. ACM DTCs are not permanent and can clear when reason for code is corrected. For additional information on SRS, see AIR BAG RESTRAINT SYSTEMS article in RESTRAINTS.