Air Bag Control Module: Description and Operation

AIR BAG AND SAFETY BELT PRETENSIONER SUPPLEMENTAL RESTRAINT SYSTEM

The air bag supplemental restraint system (SRS) is designed to provide increased collision protection for front seat and second row outboard 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 advantage of the SRS. This vehicle line contains dual stage deployment (advanced restraint system) driver and front passenger air bag modules. These vehicles can also be equipped with optional safety canopies that deploy from the A-pillar to the C-pillar upon a side impact or if a rollover condition is detected. A unique restraints control module (RCM) is used on these vehicles which will detect a potential rollover condition. In addition, a front impact severity sensor is mounted to the radiator support bracket, a seat position sensor is mounted to the driver seat and a usage detection switch is added to the front driver and passenger outboard buckles.

Restraints Control Module (RCM)

WARNING: Do not handle, move or change the original horizontal mounting position of the restraints control module (RCM) while the RCM is connected and the ignition switch is ON. Failure to follow these instructions may result in the inadvertent deployment of the safety canopy and risk of personal injury.


WARNING: The RCM orientation is critical for correct system operation. If a vehicle equipped with an air bag supplemental restraint system (SRS) 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 i& being installed If an incorrect RCM is installed erroneous DTCs will result

The restraints control module carries out the following functions:
- deploys the air bag(s) in the event of a deployable crash.
- activates the safety belt buckle pretensioners to re move slack from the safety belt.
- monitors the 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.

The RCM monitors the SRS for possible faults If a fault is detected while the ignition switch is in the ON 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 prove out by lighting for six seconds and then off for two seconds. After the prove out, the air bag indicator will then flash the two digit LFC if a SRS fault exists 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 to the scan tool. If the air bag indicator does not function, and the system detects a fault condition, 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 SRS 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 150 ms of backup power to deploy the front air bags and pretensioners in the event that the ignition circuit is lost or damaged during impact. The backup power supply will deplete its stored energy approximately one minute after the negative battery cable is disconnected.