Air Bag Systems: Description and Operation

AIRBAG SYSTEM/OCCUPANT RESTRAINT CONTROLLER SYSTEM
The 2001 Minivan Airbag System contain the following components: Occupant Restraint Controller (ORC), Airbag Warning Indicator, Clockspring, Driver and Passenger Airbags, Seat belt Tensioners (SBT), Hall-effect Seat Belt Switches (SBS), Left and Right Side Airbag Control Module (SIACM), and Seat (mounted side) Airbags.

The Occupant Restraint Controller (ORC) is a new type of Airbag Control Module (ACM) that supports staged airbag deployment. Staged deployment is the ability to trigger airbag system squib inflators all at once or individually as needed to provide the appropriate restraint for the severity of the impact. The ORC has four major functions: PCI Bus communications, onboard diagnostics, impact sensing, and component deployment. The ORC also contains an energy-storage capacitor. This capacitor stores enough electrical energy to deploy the front airbag components for two seconds following a battery disconnect or failure during an impact. The ORC is secured to the floor panel transmission tunnel below the instrument panel inside the vehicle. The ORC cannot be repaired or adjusted and must be replaced.

The ORC sends and/or receives PCI Bus messages with the Instrument Cluster (MIC), Body Control Module (BCM), and Powertrain Control Module (PCM). Diagnostic trouble codes will be set if the communication with these modules is lost or contains invalid information.

The microprocessor in the ORC monitors the impact sensor signal and the airbag system electrical circuits to determine the system readiness. The ORC also monitors bus messages from both SIACM. If the ORC detects a monitored system fault or SIACM fault, it sends a message to the instrument cluster via PCI bus to turn on the airbag warning indicator. The ORC can set both active and stored diagnostic trouble codes to aid in the diagnosing system problems. See ORC/SIACM DIAGNOSTIC TROUBLE CODES.

The ORC has an internal accelerometer that senses the rate of vehicle deceleration, which provides verification of the direction and severity of an impact. A pre-programmed decision algorithm in the ORC microprocessor determines when the deceleration rate is severe enough to require airbag system protection. The Occupant Restraint Controller (ORC) also uses the driver and front passenger seat belt switch status (buckled or unbuckled) as inputs to determine the level of airbag deployment, low, medium, or high as well as whether or not the seat belt tensioners should deploy. The ORC also uses the crash severity to determine the level of driver and front passenger deployment, low medium or high. When the programmed conditions are met, the ORC sends an electrical signal to deploy the appropriate airbag system components.

WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTRO-MECHANICAL 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 IS 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 AIRBAG CONTROL MODULE IS ACCIDENTALLY DROPPED DURING SERVICE, THE MODULE MUST BE SCRAPPED AND REPLACED WITH A NEW UNIT.

The airbag warning lamp 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 MIC performs a lamp check by turning the airbag warning indicator on for 6 - 8 seconds. After the lamp check, if the indicator turns ON, it means that the ORC 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 MIC lamp circuit may be internally 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.

FRONT AIRBAG SYSTEM
The FCM provides power to the Occupant Restraint Control (ORC) system through two "fuseless" circuits (ORC RUN/START, and ORC RUN only). These circuits are electronically controlled and continuously monitored for malfunctions. Power is supplied while the ignition switch is in the RUN and START positions on pin 48 of the FCM connector, and in the RUN only position on pin 29.

SIDE AIRBAG SYSTEM
The FCM provides power to the Side Impact Airbag Control Module (SIACM) system through one "fuseless" circuit. This circuit is electronically controlled and continuously monitored for malfunctions. Power is supplied in the ignition RUN and START positions on pin 28 of the FCM connector.