Principles of Operation
Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
Principles of Operation
In a frontal collision, the front impact severity sensors detects sudden vehicle deceleration and sends an electrical signal to the Restraints Control Module (RCM). The RCM uses the information from the front impact severity sensor, safety belt buckle switches and the Occupant Classification System Module (OCSM) to determine deployment. If the RCM determines that deployment is required, the RCM sends voltage and current to the air bag module(s) and safety belt retractor pretensioner(s).
In a side collision, the side impact sensor(s) detects sudden vehicle lateral deceleration and sends an electrical signal to the RCM. The RCM uses the information from the side impact sensor(s), safety belt buckle switches and the OCSM to determine deployment. If the RCM determines that deployment is required, the RCM sends voltage and current to the side air curtains, seat side air bag module(s) and safety belt retractor pretensioner(s).
During a frontal or side crash, the RCM may activate the side air curtains, safety belt retractor pretensioners, seat side air bag(s) and one or both stages of the driver/passenger dual-stage air bag, based on crash severity and conditions. The fact that the safety belt buckle pretensioners, adaptive load limiting retractors or air bags did not activate for both front seat occupants in a collision does not mean that something is wrong with the system.
The RCM performs a "self-test" of the complete Supplemental Restraint System (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 and 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.
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
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.
The impact sensors provide data to the RCM for use in calculating impact severity. This is accomplished using various electrical sensors located throughout the vehicle.
For these vehicles, the SRS employs up to 6 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 is 1 front impact severity sensor 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 each of the B-pillars behind the trim panels, 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 between the first and second row.
Occupant Classification Sensor (OCS) System
The Occupant Classification Sensor (OCS) system is found only on the front passenger seat. 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 system is also used for operation of the passenger Belt-Minder(R). For information on the passenger Belt-Minder(R) feature, refer to Seat Belt Systems. To deactivate or reactivate the passenger Belt-Minder(R) feature, refer to Instrument Panel, Gauges and Warning Indicators or the Owner's Literature.
When the front passenger seat is removed for service, the OCS System Reset must be carried out after the installation of the front passenger seat. When an OCS system component is installed new, the System Reset must be carried out after the installation of the front passenger seat. The Zero Seat Weight Test and/or System Reset must be carried out only as instructed to do so in the diagnostic/repair information. For information on the Zero Seat Weight Test and/or System Reset, refer to Occupant Classification Sensor (OCS) System Zero Seat Weight Test Component Tests and General Diagnostics or Occupant Classification Sensor (OCS) System Reset Programming and Relearning.
In the event of a deployable crash, a new passenger seat track with OCS weight sensor bolts must be installed. Before carrying out the OCS System Reset, on-demand DTC B1193:00 must be cleared from the OCSM. Refer to Occupant Classification Sensor Service and Repair.
The OCS weight sensor bolts are serviced as an assembly (2 weight sensor bolts and mounting bracket per side), the OCSM is serviced separately.
Occupant Classification System Module (OCSM)
Based on programmed limits, the OCSM will send the necessary information to the RCM, via a HS-CAN. The RCM uses this information in determining if the passenger air bag module or passenger seat side air bag module is to be deployed in the event of a deployable collision.
The OCSM monitors the OCS system for faults and communicates on-demand and continuous DTCs via the DLC with the use of a scan tool.
Passenger Air Bag Deactivation (PAD) Indicator
The Passenger Air Bag Deactivation (PAD) indicator is a visual indicator used to inform the front seat occupants of the passenger air bag deactivation state. The PAD indicator is located in the integrated control panel in a position visible to each front seat occupant.
The RCM controls the state of the PAD indicator through a direct hardwire connection, based on information provided by the OCS system. The PAD indicator is lit to indicate the passenger air bag module is deactivated (off). Some exceptions to this are made in certain scenarios such as 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 unlit when the passenger air bag module is activated (on).
When the ignition is in the RUN position, the PAD indicator prove-out period is initiated by the RCM. The RCM briefly activates the PAD indicator to prove-out the indicator function and verify proper functional operation.
The following table indicates the passenger air bag status and the PAD indicator status based 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.
NOTICE: Prior to installing a new Restraints Control Module (RCM), it is necessary to upload module configuration information to the scan tool. This information needs to be downloaded into the new RCM module once installed. Refer to Information Bus.
NOTE: This vehicle may be equipped with the SYNC(R) V2 feature which contains the 911 assist option. Refer to the Owner's Literature.
NOTE: Carrying out Programmable Module Installation (PMI) will not enable the 911 assist option that is disabled. The RCM and Accessory Protocol Interface Module (APIM) must be configured correctly to fully support 911 assist functionality.
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 an SRS fault exists, the RCM sends a message to 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 current SRS fault exists, the RCM requests illumination of the air bag warning indicator and will remain illuminated for the rest of the ignition cycle. The RCM will also communicate the on-demand (current) and continuous (historical) DTCs through the DLC, to the scan tool. 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 chime is a series of 5 sets of 5 tone bursts. If the chime is heard, the SRS and the air bag warning indicator require repair.
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.
Safety Belt 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 collision event force exceeding a programmed limit.
Safety Belt Buckle Switches
The 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 Sensors
The seat track position sensors are mounted to a bracket attached to the driver and passenger seat track. The seat track position sensor informs the RCM of the driver/passenger seat position. The RCM uses this information in determining the deployment of the dual-stage driver/passenger 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
A seat side air bag module provides protection of the thorax area (between the neck and abdomen) of the body, working in conjunction with the head protection provided by a side air curtain 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 driver or passenger 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:
- will deploy upon receiving a flow of current from the RCM initiated by the side impact sensors and internal RCM circuitry when a side impact is detected.
- is mounted above the headliner.
- attaches from the A-pillar frame to the C-pillar frame.
- cannot be interchanged from side to side.