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/RH front impact severity sensor (left/right frontal restraints sensor)
- Driver/Passenger first row side impact sensor B-pillar (left/right side restraints sensor 1)
- Driver/Passenger second row side impact sensor C-pillar (left/right side restraints sensor 2)
- Safety belt buckle switches (driver and passenger)
- Driver seat track position restraints sensor
- Occupant Classification System Module (OCSM)
If the RCM detects sudden vehicle deceleration and/or lateral deceleration based on 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.
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 pretensioner(s)
- Safety belt buckle pretensioner(s)
- Safety canopies
- Seat side air bag(s)
- Driver/passenger dual-stage air bag (one or both stages)
The fact that the safety belt buckle pretensioners, safety belt retractor pretensioner(s) 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 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, upon receiving a flow of current from the RCM, deploying at 1 of 2 different rates depending upon vehicle 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.
Occupant Classification Sensor (OCS) System
The Occupant Classification Sensor (OCS) system is found only on the front passenger seat. 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 OCSM will inform the RCM.
The OCSM monitors OCS system for faults.
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.
Belt Tension Sensor (BTS)
The Belt Tension Sensor (BTS):
- is a 3-wire Hall-effect sensor located at the safety belt anchor point and is part of the front passenger safety belt and retractor assembly.
- is used in conjunction with the OCS system.
The BTS is used by the OCS system to identify the presence of a child safety seat on the front passenger seat. The BTS senses the tension on the safety belt assembly then provides an output to the OCSM, indicating that the safety belt assembly is cinched. After sensing the weight applied to the seat by the occupant and using the 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 PAD indicator through a direct hardwire connection, 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.
NOTICE: When installing a new Restraints Control Module (RCM), it is necessary to carry out Programmable Module Installation (PMI). System failure may occur if PMI is not performed. For additional information, refer to Information Bus. Programming and Relearning
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.
NOTE: This vehicle may be equipped with the SYNC(R) V2 feature which contains the 911 assist option. Refer to Owner's Literature.
The RCM carries out the following functions:
- Deploys the air bag(s)/safety canopies 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 deployable collision
- Activates the driver and passenger retractor pretensioner(s) to control the tension of the driver and passenger safety belts in the event of a deployable collision
- Monitors the SRS for faults
- Sends a message to the IC 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 IC module to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IC module will prove out the air bag warning indicator by lighting for 6 seconds. If no faults are detected by the RCM, the IC 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 IC 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 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.
Event Notification Signal
A hardwired interface from the RCM that is used to notify other subsystems that a restraints event has occurred.
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. Events that may trigger the impact event notification feature include but are not limited to:
- Deployment of any deployable device
- Trigger events
- Fuel cutoff events
Each method of notification provides indication of normal operation, a deployment event or fuel cutoff event. Supplemental event data may also be available via the HS-CAN network.
The event notification signal is provided by the RCM to the fuel pump control module. 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 event notification signal consists of a hardwired Pulse Width Modulated (PWM) signal from the RCM and transmitted to the fuel pump control module. The PCM monitors the event notification signal circuit from the fuel pump control module for faults and will set a DTC and turn ON the wrench light if a fault is detected with the event notification signal circuit. The RCM does not monitor for any circuit faults and will not set a DTC if a fault occurs.
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 IC 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 Buckle Pretensioners
The safety belt buckle pretensioners are pyrotechnic devices integrated to the driver and passenger safety belt buckle assemblies. 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 Retractor Pretensioner
Safety belt retractor pretensioners are pyrotechnic devices integrated to the safety belt retractor assemblies. Safety belt retractor pretensioners work in conjunction with the safety belt buckle pretensioners and control the tension of the driver and passenger seat belts in the event of a deployable collision.
Safety Canopy(R) Module
WARNING: Anytime the Safety Canopy(R) or side air curtain module has deployed, a new headliner and new A-, B-, C- and D-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.
NOTE: There are different Safety Canopy(R) modules for vehicles equipped with a moon roof and vehicles without a moon roof. The Safety Canopy(R) modules are NOT interchangeable. If installing a new Safety Canopy(R) module, the correct Safety Canopy(R) module MUST be installed for the vehicle application.
The Safety Canopy(R) module:
- is installed as an assembly.
- is mounted above the headliner.
- attaches from the A-pillar frame to the C-pillar frame.
Seat Track Position Sensor
The driver seat is equipped with a seat track position sensor. The seat track position sensor is comprised of integrated circuits called a Hall-effect switch. 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 rate of the dual-stage driver air bag module.
Secondary Air Bag Warning (Chime)
The secondary air bag warning chime is an audible chime located in and controlled by the IC module. If a fault is detected with the air bag warning indicator, a DTC will be stored in 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.
Impact Sensors (Restraints Sensor)
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 (frontal restraints sensor) located in the front of the vehicle, behind the grille mounted on the radiator support. The first row impact sensors (side restraints sensor 1) are mounted behind the trim panel near the floor on the B-pillar, the second row sensors (side restraints sensor 2) are located on each C-pillar. Mounting orientation is critical for correct operation of all impact sensors.
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.
The side air bag module:
- will deploy upon receiving a flow of current from the RCM, initiated by the side restraints sensor and internal RCM circuitry.
- is mounted in the seat backrest.
- is used in conjunction with a Safety Canopy(R) module.