Air Bag Control Module: Description and Operation

RESTRAINTS CONTROL MODULE (RCM)

WARNING: The restraints control module (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, a new RCM must be installed whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting area 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 carries out the following functions:
- Signals the inflators to deploy the air bags in the event of a deployable crash.
- Activates the steering column squib to help reduce the force needed to collapse the steering column.
- Activates the safety belt retractor pretensioners to remove slack from the safety belt.
- Monitors the air bag SRS for faults.
- Illuminates the air bag indicator if a fault is detected.
- Receives information from the front and side impact sensors.
- Sends safety belt buckle status to the instrument cluster for safety belt lamp and Belt Minder.
- 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 to activate a chime if a fault is detected.
- 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 ON position, the RCM will illuminate the air bag indicator located in the instrument cluster and signal the instrument cluster to activate the chime.

The chime is a series of 5 sets of 5-tone bursts. If the chime is heard and/or the air bag indicator is illuminated, the SRS and the air bag indicator require repair. When the ignition is cycled (turned off and then on), the air bag indicator will remain lit for 6 seconds and then go out. If a SRS fault exists, the air bag indicator will then flash the 2-digit LFC. The air bag indicator will flash the LFC 5 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 data link connector (DLC), using the diagnostic tool.

LFCs are prioritized. If 2 or more 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 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 air bag deployment is activated. The backup power supply will deplete its stored energy approximately one minute after the power is removed from the RCM.