Air Bag Control Module: Description and Operation

AIR BAG SYSTEM DESCRIPTION

The air bag system is designed to provide increased collision protection for front seat occupants in addition to that provided by the three-point safety belt system. Safety belt use is necessary to obtain the best occupant protection and to receive the full advantages of the system.

Air Bag System Component View:

Air bag system components are as shown in the illustration.

Restraints Control Module (RCM)

WARNING: The restraints control module (RCM) orientation is critical for correct air bag supplemental restraint system (SRS) operation. If a vehicle equipped with an SRS 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 RCM must be replaced whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting is restored to its original condition.

NOTE: When installing a new restraints control module (RCM), always make sure the correct RCM is being installed If an incorrect RCM is installed, erroneous DTCs will result.

The restraints control module (RCM) is mounted on the center tunnel under the instrument panel The RCM performs the following functions.
- signals the inflators to deploy the air bags in the event of a deployable crash.
- activates the safety belt buckle pretensioners to remove slack from the safety belt.
- monitors the air bag supplemental restraint system (SRS) for faults.
- illuminates the air bag indicator if a fault is detected.
- flashes the air bag indicator to indicate the lamp fault code (LFC) detected.
- communicates through the data link connector (DLC) the current or historical diagnostic trouble codes (DTCs).
- signals the instrument cluster module to activate a chime if the air bag indicator is not available and another SRS fault exists.
- contains an internal safing sensor which is not serviced separately.

The RCM monitors the SRS for possible faults. If a fault is detected while the ignition switch is in the RUN position, the RCM 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 RCM will also communicate the current and historical DTCs through the DLC, using the diagnostic tool If the air bag indicator does not function, and a system fault is detected, the RCM will signal the instrument cluster module 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 RCM 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 negative battery 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 RCM to both air bag modules.
- provides the electrical path from the RCM to the air bag indicator.
- provides the electrical path from the RCM to the data link connector (DLC).
- provides the electrical path from the RCM to the instrument cluster module.