Air Bag Control Module: Description and Operation

Air Bag Diagnostic Monitor





The air bag diagnostic monitor continually monitors all air bag system components and wiring connections for possible faults in the system. If the diagnostic monitor detects a fault in the air bag system when the ignition switch is in RUN, a diagnostic trouble code will be displayed on the air bag indicator, located in the instrument cluster. Performing system diagnostics is the main purpose of the diagnostic monitor.

The air bag diagnostic monitor does not deploy the air bags in the event of a crash. The crash sensors are "hard wired" to the air bags, therefore, the crash sensor and safing sensor determine when to deploy the air bags.

Features and functions of the air bag diagnostic monitor include:
- The air bag diagnostic monitor illuminates the air bag indicator for approximately six seconds when the ignition switch is in RUN and then turns the lamp off. This indicates that the air bag indicator is operational. If the air bag indicator does not illuminate, stays on or flashes at any time, a fault has been detected by the air bag diagnostic monitor.
- Fault codes may not be displayed for approximately 45 seconds after the ignition switch is placed in the ON position. This is the amount of time the air bag diagnostic monitor requires to perform all tests and verify system faults, if present.
- Fault codes are displayed as a series of flashes and pauses of the air bag indicator. Each diagnostic trouble code (series of flashes) represents a two-digit number. For example, a diagnostic trouble code 32 is displayed as follows:
- Three flashes, followed by a one second pause, then two flashes, followed by a three second pause.
- Three flashes, followed by a one second pause, then two flashes, followed by a three second pause.
- If a system fault is present and the air bag indicator is malfunctioning, an audible tone will be heard, indicating that system service is required. The tone is a series of five sets of five beeps. This does not indicate a diagnostic trouble code 55. If the tone is heard, the air bag indicator is inoperative and a system fault that requires service is present.
- If a fault exists that makes unwanted air bag deployment possible, the air bag diagnostic monitor has an internal thermal fuse that will blow (open) automatically. This removes all power to the air bag deployment circuit. The air bag indicator will flash the appropriate diagnostic trouble code to indicate the suspect circuit.

CAUTION: The thermal fuse does not blow (open) because of excessive current flowing through it. DO NOT attempt to short circuit the thermal fuse with a circuit breaker or any other type of fuse.

- Fault codes are prioritized numerically so that if two or more different faults occur at the same time, the fault having the highest priority will be displayed first. After that fault has been corrected, the next highest priority diagnostic trouble code will be displayed. The diagnostic trouble code will repeat continuously.
- 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 and safing sensors close. The backup power supply will deplete its stored energy approximately one minute after the positive battery cable is disconnected.

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 POSITIVE BATTERY CABLE AND WAIT ONE MINUTE.