Air Bag Control Module: Description and Operation

Air bag system components are shown in the following illustration.

Air Bag Diagnostic Monitor
The air bag diagnostic monitor performs the following functions:
- signals the inflators to deploy the air bags in the event of a deployable crash.
- monitors the air bag system for faults.
- illuminates the air bag indicator if a fault is detected.
- flashes the air bag indicator to indicate a lamp fault code (LFC) is detected.
- communicates through the data link connector (DLC) the current or historical diagnostic trouble codes (DTCs).
- signals the generic electronic module (GEM) to activate a chime if the air bag indicator is not available and another system fault exists.

NOTE: The safing sensor is internal to the air bag diagnostic monitor and is not serviced separately.

The air bag diagnostic monitor checks the air bag system for possible faults. If a fault is detected while the ignition switch is in the ON position, the air bag diagnostic monitor will illuminate the air bag indicator located in the instrument cluster.

When the ignition is cycled (turned OFF and then ON), the air bag indicator will remain lit for six seconds and then go out for two seconds. If an air bag system fault exists, the air bag indicator will then flash a two-digit lamp fault code (LFC). The air bag indicator will flash the LFC five times, then it will remain illuminated for the rest of the key cycle. The air bag diagnostic monitor will also communicate the current and historical DTCs through the DLC, using the NGS Tester. If the air bag indicator does not function, and a system fault is detected, the air bag diagnostic monitor will signal the GEM to activate an audible chime. The chime is a series of five sets of five tone bursts. If the chime is heard, the air bag system and the air bag indicator require repair.

LFCs are prioritized. If two or more faults occur at the same time, the fault having the highest priority will be displayed. After that fault has been corrected, the next highest priority fault will be displayed.

The air bag system diagnostic monitor includes a backup power supply. This feature provides sufficient backup power to deploy the air bags in the event that the ignition circuit is damaged in a collision before the safing and air bag sensors determine that a deployment is required. The backup power supply will deplete its stored energy approximately 1 minute after the battery ground cable is disconnected.

Electrical System
The electrical system that supports the air bag system:
- is powered from the battery through the ignition circuit.
- provides the electrical path from the air bag diagnostic monitor to both air bag modules.
- provides the electrical path from the air bag diagnostic monitor to the air bag indicator.
- provides the electrical path from the air bag diagnostic monitor to the data link connector (DLC).
- provides the electrical path from the air bag diagnostic monitor to the GEM module.

Sensor

WARNING:
- The air bag diagnostic monitor orientation is critical for correct air bag system operation. If a vehicle equipped with an air bag system has been involved in a collision in which the center tunnel area has been damaged, inspect the mounting and bracket for deformation. If damaged, the air bag diagnostic monitor must be Installed new whether or not the air bag modules have deployed. In addition, make sure the area of the air bag diagnostic monitor mounting is restored to Its original condition.

The air bag system contains two sensors which are integral to the air bag diagnostic monitor. The air bag diagnostic monitor is mounted on the center tunnel under the instrument panel.