Air Bag Control Module: Description and Operation

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.
- writes a Diagnostic Trouble Code (DTC) to air bag diagnostic monitor's Non-Volatile Random Access Memory (NVRAM) if it detects a concern in the air bag system. After servicing, the DTC may then be cleared from NVRAM.
- turns the air bag indicator ON if it detects a concern in the air bag system.
- performs system diagnostics, which is its main function.
- does not deploy the air bags in the event of a collision.
- the crash sensors are hard wired to the air bags. Thus, the crash sensors determine when the air bag will be deployed.
- monitors the system for readiness and has crash sensors which determine air bag deployment.

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.





Air Bag System Functions
- The air bag diagnostic monitor illuminates the air bag indicator for approximately six seconds when the ignition switch is turned to RUN 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, if present, will begin flashing within 30 seconds after the ignition switch has been turned to RUN. 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 displayed as a series of flashes and pauses of the air bag indicator. Diagnostic trouble codes are two-digit numbers.

Example: A DTC 32 is displayed as follows:
flash flash flash - (two second pause) - flash flash - (five second pause)... flash flash flash - (two second pause) - flash flash - (five second pause)...

- Diagnostic trouble codes are prioritized numerically so that if two or more faults occur at the same time, the diagnostic trouble code with the highest priority will be displayed.
- After the DTC is displayed five times, the air bag indicator will illuminate continuously until the ignition switch is cycled.
- The air bag diagnostic monitor incorporates Non-Volatile Random Access Memory (NVRAM) to store diagnostic trouble codes and retain them indefinitely. The air bag diagnostic monitor will always flash the highest priority diagnostic trouble code stored in NVRAM. Diagnostic trouble codes may be cleared from the air bag diagnostic monitor after the fault conditions are serviced.
- The air bag diagnostic monitor distinguishes between hard and intermittent (or repaired) fault conditions.

Each diagnostic trouble code number 12-45 represents a hard fault (a fault that is still present). Hard diagnostic trouble codes are higher priority than intermittent diagnostic trouble codes and may not be cleared from NVRAM.

Each of these hard diagnostic trouble codes has an equivalent diagnostic trouble code which is the sum of the diagnostic trouble code number plus 40. This equivalent diagnostic trouble code will indicate that an intermittent condition exists or that a hard condition has been repaired.

Only the intermittent (repaired) diagnostic trouble codes, numbers 52-85, may be cleared from the air bag diagnostic monitor. Example: A Diagnostic Trouble Code 32 indicates that high resistance in the driver side air bag circuit has been, and still is, present. A DTC 72 (32 + 40) indicates that high resistance in the driver side air bag circuit existed at one time, but no longer exists due to an intermittent condition or a repair made to the circuit.

- If a system fault exists and the air bag warning 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 55 or any other diagnostic trouble code. The air bag warning indicator must be serviced before diagnostic trouble codes can be determined.

WARNING: UNDER NO CIRCUMSTANCES SUBSTITUTE ANOTHER FUSE VALUE FOR THE 1OA BATTERY FUSE. ANY FUSE OTHER THAN 1OA MAY CAUSE DISARMING FAILURE AND MAY RESULT IN DANGER TO THE OCCUPANTS OF THE VEHICLE. DO NOT ATTEMPT TO REPLACE THE 1OA 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 10A battery fuse.

-If the 1OA 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. The air bag diagnostic monitor will store both the unwanted deployment diagnostic trouble code and the loss of deployment power diagnostic trouble code. The loss of deployment power diagnostic trouble code is the highest priority.

WARNING: THE BACK-UP POWER SUPPLY ENERGY MUST BE DEPLETED BEFORE ANY AIR BAG COMPONENT SERVICE IS PERFORMED. TO DEPLETE THE BACK-UP 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 back-up power supply. This feature provides sufficient back-up 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 back-up 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.