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 sensors
- Driver and passenger front door side impact sensors
- Driver and passenger second row C-pillar side impact sensors
- Safety belt buckle switches (driver and passenger)
- Driver and passenger seat track position sensors
- Occupant Classification System Module (OCSM)
If the RCM detects sudden vehicle deceleration and/or lateral deceleration based on information received from sensors and switches and determines that deployment is required, the RCM sends voltage and current to deploy the appropriate SRS components.
The RCM contains an internal sensor that detects vehicle rollover angles. If the RCM determines that a rollover condition exists and deployment is required, the RCM deploys the applicable 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
- Safety belt buckle pretensioner(s)
- Safety Canopy(R)
- Seat side air bag(s)
- Driver and passenger dual-stage air bags (one or both stages)
- Deployable steering column
The fact that the safety belt buckle pretensioner(s), safety belt retractor(s) or air bag(s) did not activate for both front seat occupants in a crash does not mean that something is wrong with the SRS system.
The RCM performs a self-test of the complete 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 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.
Air Bag Warning Indicator
The air bag warning indicator:
- located in the Instrument Panel Cluster (IPC) module, will prove out by lighting for 6 seconds and then turn off.
- will flash and/or illuminate based on the message the IPC module receives from the RCM.
- will illuminate if the IPC module does not receive a message from the RCM.
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, upon receiving a flow of current from the RCM, deploying at 1 of 2 different rates depending upon vehicle impact severity and sensor input.
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 the event notification signal circuit for faults and will not set a DTC if a fault occurs.
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 information about the HS-CAN.
Impact Sensors
For this vehicle line, the SRS uses 6 satellite sensors in addition to the RCM. The RCM is mounted to the center tunnel beneath the console. All vehicles have 2 front impact severity sensors located in the front of the vehicle. The first row impact sensors are mounted to each front door behind the trim panel, the second row sensors are located on each C-pillar. Mounting orientation is critical for correct operation of all impact sensors.
Occupant Classification Sensor (OCS) System
The Occupant Classification Sensor (OCS) system is found only on the front passenger seat. The OCS system classifies the size of 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 and safety belt pretensioner.
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 Collision Avoidance and Parking Assist Systems or the Owner's Literature.
This vehicle line utilizes 2 different types of OCS systems based on seating option(s), bladder system or weight sensor bolt system.
Occupant Classification Sensor (OCS) System - Bladder System
The OCS system is comprised of a silicone gel-filled bladder mounted between the seat cushion foam and pan, a pressure sensor that is mounted to the seat frame and an OCSM which is also mounted to the seat frame. Pressure is applied to the OCS system bladder when weight of any occupant or object in the front passenger seat is present. The pressure is then transferred through a tube, sensed by the OCS system pressure sensor, then electronically communicated to the OCSM. The components of an OCS bladder system (bladder, pressure sensor and tube, OCSM) are serviced as an assembly.
Occupant Classification Sensor (OCS) System - Weight Sensor Bolt System
The OCS system is comprised of 4 OCS weight sensor bolts that are mounted to each corner of the seat track and serviced as an assembly with the seat track. The OCSM is mounted to the electrical bracket underneath the seat cushion pan and can be serviced separately from the seat track assembly. The weight of any occupant or object on the front passenger seat is electronically communicated to the OCSM.
Belt Tension Sensor (BTS)
The Belt Tension Sensor (BTS):
- is a 3-wire Hall-effect sensor and is part of the front passenger safety belt and retractor assembly.
- is used in conjunction with the OCS system.
The BTS is used to identify the presence of a child safety seat on the front passenger seat. The BTS senses the tension on the safety belt then provides an output to the OCSM, indicating that the safety belt is cinched. After sensing the weight applied to the seat or using BTS input, the OCSM determines how the occupant should be classified and communicates this information to the RCM. If the occupant is classified as a child, the RCM will then automatically deactivate the passenger air bag module and illuminate the Passenger Air Bag Deactivation (PAD) indicator.
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 illuminated to indicate the passenger air bag module is disabled. An exemption 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 other 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 Passenger Air Bag Deactivation (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 vehicle impact severity and sensor input.
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 this instruction may result in the accidental deployment of the Safety Canopy(R) and cause serious personal injury or death.
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)/Safety Canopy(R) in the event of a deployable collision
- Activates the safety belt buckle pretensioners to remove slack from the safety belt in the event of a crash
- Activates the driver and passenger retractor to control the tension of the driver and passenger safety belts in the event of a crash
- Monitors the SRS for faults
- Sends a message to the IPC module to illuminate the air bag warning indicator if a fault is detected
The RCM monitors the SRS for possible faults. If a fault is detected, the RCM will request the IPC module to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IPC module will prove out the air bag warning indicator by lighting for 6 seconds. If no faults are detected by the RCM, the IPC module will turn the air bag warning indicator off and it will remain off. If the RCM detects a fault, it will send a message to the IPC module to turn the air bag warning indicator on and it will remain on 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 IPC 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.
Safety Belt Buckle Pretensioners
The safety belt buckle 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
The safety belt buckles are comprised of integrated circuits called Hall-effect switches. The safety belt buckle switches indicate to the RCM whether the safety belts are buckled or unbuckled.
The RCM also communicates the driver safety belt buckle switch status to the IPC module, which monitors the information to control the safety belt warning indicator. For information on the safety belt warning indicator, refer to Instrument Panel, Gauges and Warning Indicators.
Safety Belt Retractor
The front safety belt retractor is equipped with the adaptive load limiting feature that works in conjunction with the safety belt buckle pretensioner to control the tension of the driver and passenger safety belts in the event of a crash. The front safety belt retractor is also referred to as the Seatbelt Load limiter.
Safety Canopy(R) 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 Safety Canopy(R) module:
- is mounted above the headliner.
- attaches from the A-pillar frame to the C-pillar frame.
Seat Side Air Bag Module
The side air bag module:
- will deploy upon receiving a flow of current from the RCM, initiated by the RCM.
- is mounted in the seat backrest.
- is used in conjunction with a Safety Canopy(R) module.
Seat Track Position Sensor
The seat track position sensor indicates to the RCM the position of the seat, forward or rearward. The RCM uses this information in determining the deployment rate of the dual-stage driver and passenger air bag modules.
Secondary Air Bag Warning (Chime)
The secondary air bag warning chime is an audible chime located in and controlled by the IPC module. If a fault is detected with the air bag warning indicator, a DTC will be stored in memory of the IPC module. Upon receiving the message from the RCM that a SRS fault has been detected, the IPC module will sound the secondary air bag warning chime in a pattern of 5 sets of 5 beeps.