Principles of Operation
Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
Principles of Operation
The Restraints Control Module (RCM) continuously receives/monitors all inputs from the following Supplemental Restraint System (SRS) components.
- LH and RH front impact severity sensor
- Driver and Passenger B-pillar side impact sensor
- Driver and Passenger C-pillar side impact sensor
- Safety belt buckle switches (driver and passenger)
- Driver seat track position sensor
- Occupant Classification System Module (OCSM)
If the RCM detects sudden vehicle deceleration and/or lateral deceleration based on all the information received from all sensors and switches and determines that deployment is required, the RCM sends voltage and current to deploy the appropriate SRS components.
During a frontal or side crash, the RCM may deploy the following SRS components, based on crash severity and sensor input.
- Safety belt retractor pretensioner(s)
- Seat side air bag(s)
- Side air curtain(s)
- Driver/passenger dual-stage air bag (one or both stages)
The fact that the safety belt retractor pretensioners, side air curtains and side air bags did not activate for both front seat occupants in a crash does not mean that something is wrong with the system.
The RCM performs a self-test of the SRS during each startup. If a SRS fault exists, the air bag warning indicator will illuminate and remain illuminated for the rest of the ignition cycle. In addition to the self-test at start up, the RCM continuously monitors all of its SRS components and circuitry for correct operation.
Air Bag Warning Indicator
The air bag warning indicator:
- located in the Instrument Cluster (IC) module will prove out by lighting for 6 seconds then turn off.
- will flash and/or illuminate based on the message the IC module receives from the RCM.
- will illuminate if the IC module does not receive a message from the RCM.
Air Bag Module Second Stage Deployment Check
Because the driver and passenger front air bags each have 2 deployment stages, it is possible that stage 1 has deployed and stage 2 has not.
If a front air bag module has deployed, it is mandatory that the front air bag module be remotely deployed using the appropriate air bag disposal procedure.
- For information on driver air bag module and/or passenger air bag module remote deployment, refer to Pyrotechnic Device Disposal Service and Repair.
Clockspring
The clockspring allows for continuous electrical connections between the driver air bag module and the RCM when the steering wheel is turned.
Driver Air Bag Module
The driver air bag module is a dual-stage air bag, deploying at 1 of 2 different rates depending upon impact severity and sensor input.
High Speed Controller Area Network (HS-CAN)
This vehicle utilizes a communication system called a High Speed Controller Area Network (HS-CAN). The RCM communicates with various modules for required information about the vehicle. Refer to Information Bus for additional information about the HS-CAN.
Impact Sensors
For these vehicles, the SRS employs 7 impact sensors. One of the sensors is integral to the RCM and is not separately serviceable. The RCM is mounted on the center tunnel between the front seats. There are 2 front impact severity sensors located in the front-center of the vehicle, behind the grille. In addition, there are 4 side impact sensors. The first row side impact sensors are located on or near the base of the B-pillar, the second row side sensors are located on or near the base of the C-pillar. Mounting orientation is critical for correct operation of all impact sensors.
The side impact sensors are not interchangeable.
Occupant Classification Sensor (OCS) System
The Occupant Classification Sensor (OCS) system is found only on the front passenger seat. The OCS system classified the size of the front passenger seat occupant and provides this information to the Restraints Control Module (RCM). The RCM uses this information (and other inputs) in determining the deployment strategy of the passenger air bag module and pretensioner. The front passenger OCS system is comprised of the following: 4 OCS weight sensor bolts that are mounted to each corner of the seat track and an OCSM which is mounted to the electrical bracket underneath the seat cushion pan. The weight of any occupant or object on the front passenger seat is electronically communicated to the OCSM. The OCS weight sensor bolts are serviced as an assembly (2 weight sensor bolts and mounting bracket per side), the OCSM is serviced separately.
The OCS system is also used for operation of the passenger Belt-Minder(R). For information on the passenger Belt-Minder(R) feature, refer to Restraint Systems. To deactivate or reactivate the passenger Belt-Minder(R) feature, refer to Instrument Panel, Gauges and Warning Indicators or the Owner's Literature.
Passenger Air Bag Deactivation (PAD) Indicator
The RCM controls the state of the Passenger Air Bag Deactivation (PAD) indicator, based on information provided by the OCS system. The PAD indicator is lit to indicate the front passenger air bag module is disabled. An exception to this is when the front passenger seat is determined to be empty, and therefore indication of a deactivated passenger air bag module is not necessary. In all cases, the PAD indicator is off when the passenger air bag module is enabled.
The RCM briefly activates the PAD indicator to prove-out the indicator function and verify to the front occupants correct functional operation of the PAD indicator.
The following table indicates the passenger air bag status and the PAD indicator status based on the size of the front passenger occupant.
Passenger Air Bag and PAD Indicator Status
Passenger Air Bag Module
The passenger air bag module is a dual-stage air bag, deploying at 1 of 2 different rates depending upon impact severity, sensor input, safety belt usage and passenger seat occupant classification.
Restraints Control Module (RCM)
WARNING: If a vehicle has been in a crash, inspect the restraints control module (RCM) and the impact sensor (if equipped) mounting areas for deformation. If damaged, restore the mounting areas to the original production configuration. A new RCM and sensors must be installed whether or not the air bags have deployed. Failure to follow these instructions may result in serious personal injury or death in a crash.
NOTE: This vehicle is equipped with the SYNC(R) feature which contains the 911 assist option. Refer to the Owner's Literature.
The RCM carries out the following functions:
- Deploys the air bag(s)/side air curtain(s) in the event of a deployable collision
- Activates the safety belt retractor pretensioner to control tension on the safety belt in the event of a deployable collision
- Monitors the SRS for faults
- Sends a message to the IC module to flash/illuminate the air bag warning indicator if a fault is detected
- Communicates through the DLC the current or historical DTCs
The RCM monitors the SRS for possible faults. If a SRS fault exists, the RCM sends a message to the IC module to illuminate the air bag warning indicator.
When the ignition is cycled (OFF and then ON), the IC module will prove out the air bag warning indicator by lighting for 6 seconds and then turn off. If a fault is detected, the RCM requests illumination of the air bag warning indicator and will remain illuminated for the rest of the ignition cycle. If the RCM requests illumination of the air bag warning indicator and the air bag warning indicator does not function, the IC module will automatically activate an audible chime.
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 lost or damaged during impact. The backup power supply will deplete its stored energy approximately one minute after power and/or ground has been removed from the RCM.
Event Notification Signal
The purpose of the deployment event notification feature is to provide other vehicle subsystems with information pertaining to restraint system deployment or fuel cutoff status. Signal communication between the RCM and fuel pump control module allows the PCM to initiate fuel cut-off to disable the fuel system in the event of a crash.
The RCM does not monitor for any circuit faults and will not set a DTC if a fault occurs.
Safety Belt Retractor Pretensioners
The safety belt retractor pretensioners remove excess slack from the safety belt webbing. The pretensioners are activated by the RCM when the module detects a crash event force exceeding a programmed limit.
Safety Belt Buckle Switches
Safety belt buckle switches indicate to the RCM whether the safety belts are buckled or unbuckled. The RCM uses this information in determining the deployment of the dual-stage driver and passenger air bag modules.
Seat Track Position Sensor
The seat track position sensor indicates to the RCM the position of the driver seat, forward or rearward. The RCM uses this information in determining the deployment of the dual-stage driver air bag module.
Secondary Air Bag Warning (Chime)
The secondary air bag warning chime, is an audible chime controlled by the IC module. If the IC module has detected a fault with the air bag warning indicator, a DTC will be stored in the memory of the IC module. Upon receiving the message from the RCM that a SRS fault has been detected, the IC module will sound the secondary air bag warning chime in a pattern of 5 sets of 5 beeps.
Seat Side Air Bag Module
The seat side air bag module:
- will deploy upon receiving a flow of current from the RCM, initiated by the side impact sensor and internal RCM circuitry.
- is mounted in the seat backrest.
- is used in conjunction with a side air curtain module.
Side Air Curtain Module
WARNING: Anytime the Safety Canopy(R) or side air curtain module has deployed, a new headliner and new A-, B- and C-pillar upper trim panels and attaching hardware must be installed. Remove any other damaged components and hardware and install new components and hardware as needed. Failure to follow these instructions may result in the Safety Canopy(R) or side air curtain module deploying incorrectly and increases the risk of serious personal injury or death in a crash.
The side air curtain module:
- is mounted above the headliner.
- attaches from the A-pillar frame to the C-pillar frame.