Air Bag Control Module: Description and Operation

PURPOSE
The air bag diagnostic monitor performs system diagnostics, which is its main function. The air bag diagnostic monitor continually monitors all air bag system components and wiring connections for possible faults when the ignition switch is in the RUN position.

OPERATION
The air bag diagnostic monitor does NOT deploy the air bags in the event of a collision. It operates in the following manner:
- If a fault is detected in the air bag system, the air bag diagnostic module writes a Diagnostic Trouble Code (DTC) to air bag diagnostic monitor's Non-Volatile Random Access Memory (NVRAM) it detects a concern in the air bag system.
- This DTC will display on the the AIR BAG indicator.
- After servicing, the DTC may then be cleared from NVRAM.
- monitors the system for readiness and has crash sensors which determine air bag deployment.

AIR BAG SYSTEM FUNCTIONS
Several important features of the air bag diagnostic monitor and its functions within the system are described below. It is necessary that these key features and functions are well understood.






- The air bag diagnostic monitor illuminates the air bag indicator for approximately 6 seconds when the ignition switch is turned to the RUN position and then turns the air bag indicator off. This indicates that the air bag indicator is operational. If the air bag indicator does not illuminate at all, stays on continuously or flashes at any time, then a fault has been detected by the air bag diagnostic monitor.

- Diagnostic Trouble Codes (DTCs), if present, will cause the AIR BAG indicator to begin flashing within 30 seconds after the ignition switch has been turned to the RUN position. This is the amount of time it takes the air bag diagnostic monitor to perform all tests and verify system faults, if present.

- Diagnostic trouble codes are retrieved using the Rotunda New Generation STAR (NGS) Tester 007-00500.

- The air bag diagnostic monitor incorporates Non-Volatile Random Access Memory (NVRAM) to store diagnostic trouble codes and retain them indefinitely. Diagnostic trouble codes may be cleared from the air bag diagnostic monitor after the fault conditions are serviced as outlined under Testing and Inspection / Diagnostic Methods Overview.

- If a system fault exists and the air bag indicator is not functioning, an audible tone will be heard indicating a need for service. The tone is a series of five sets of five beeps. This does not indicate a diagnostic trouble code. The AIR BAG indicator must be serviced before diagnostic trouble codes can be determined.

WARNING: Under no circumstances substitute another fuse value for the 10 A battery fuse. Any fuse other than 10 A may cause disarming failure and may result in danger to the occupants of the vehicle. Do not attempt to replace the 10 A battery fuse until the air bag system first has been deactivated.

- If a fault exists that makes unwanted air bag deployment possible, the air bag diagnostic monitor will attempt to remove deployment power by turning on a solid state switch to blow the 10 A battery fuse.

- If the 10 A battery fuse has successfully been blown by the air bag diagnostic monitor, the air bag diagnostic monitor will not attempt to blow it again until the proper fault has been serviced and cleared (refer to Testing and Inspection / Clearing and Extracting Codes). The air bag diagnostic monitor will store both the diagnostic trouble code that caused it to blow the 10 A battery fuse and the loss of deployment power diagnostic trouble code (DTC B1867). The loss of deployment power diagnostic trouble code is the highest priority.

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 negative battery cable and wait one minute to avoid accidental deployment and possible personal injury.

- The air bag diagnostic monitor includes an internal backup power supply. This feature provides sufficient backup power to deploy the air bags in the event that the battery or battery cables are damaged in a collision before the crash sensors are activated. The backup power supply will deplete its stored energy approximately one minute after the negative battery cable is disconnected.

- The air bag diagnostic monitor incorporates an internal safing sensor. Proper mounting of the air bag diagnostic monitor and bracket assembly is critical to the function and performance of the air bag system.

- The air bag diagnostic monitor and bracket assembly is non-serviceable and must be replaced as a unit in the event of failure.