Airbag System: Notes

The Airbag system is equipped with two types of Occupant Restraint Controller or ORC, base and premium. The ORC is a specific type of Airbag Control Module or ACM. The term Airbag Control Module or ACM will be used throughout the airbag diagnostic procedures and the Diagnostic Readout Box or DRB III(R). The DRB III(R) is a scan tool use to interrogate the ACM to retrieve Diagnostic Trouble Codes or DTC's and other system information.

The ACM is secured to a bracket on the floor panel transmission tunnel between the floor shifter and parking brake. The ACM contains a microprocessor, the impact sensor, and energy storage capacitors. The microprocessor contains the airbag system logic. The airbag system logic includes On-Board Diagnostics OBD capability, and communicates with the instrument cluster circuitry on the Programmable Communication Interface (PCI) data bus to control the airbag warning indicator. The microprocessor in the ACM monitors the internal and external circuits to determine the system readiness. If the ACM detects a monitored system fault, it sends messages to the Mechanical Instrument Cluster (MIC) over the PCI data bus to turn on the Airbag Warning Indicator and provides the electrical signal to deploy the airbag system components. The impact sensor is an accelerometer that senses the rate of vehicle deceleration, which provides verification of the direction and severity of an impact. The impact sensor is calibrated for the specific vehicle, and is only serviced as a unit with the ACM. The ACM also contains an energy-storage capacitor. This capacitor stores enough electrical energy to deploy the airbags if the initial impact has damaged or disconnected the battery, but not severe enough to deploy the airbags. The ACM cannot be repaired or adjusted and, if damaged or faulty, it must be replaced.

The Base ACM can be identified by the present of a single yellow 23- way connector. This module supports the Driver and Passenger Seat Belt Tensioners and dual squib airbags.

The Premium ACM can be identified by the present of a two yellow 32-way connectors and the presents of side curtain airbag. In addition to the base system components and DTC's the premium ACM supports the Side Impact Sensors, Side Curtain Airbags, and an accelerometer that provides verification of the direction and severity of an impact from the front and both sides. In addition to the base ACM DTCs the premium ACM provides DTC's for the additional circuit and component.

WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENTS YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. WAIT TWO MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY. NEVER STRIKE OR KICK THE AIRBAG CONTROL MODULE, AS IT CAN DAMAGE THE IMPACT SENSOR OR AFFECT ITS CALIBRATION. IF AN OCCUPANT RESTRAINT CONTROLLER IS ACCIDENTALLY DROPPED DURING SERVICE, THE MODULE MUST BE SCRAPPED AND REPLACED WITH A NEW UNIT.

The Airbag Warning Indicator is the only point at which the customer can observe "symptoms" of a system malfunction. Whenever the ignition key is turned to the "run" or "start" position, the ACM performs a lamp check by turning the AIRBAG warning lamp on for 6 to 8 seconds. If the lamp remains off, it means that the ORC has checked the system and found it to be free of discernible malfunctions. If the indicator remains on, there could be an active fault in the ACM system.