Restraints and Safety Systems: Description and 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 front impact severity sensor (left frontal restraints sensor)
- RH front impact severity sensor (right frontal restraints sensor)
- Driver first row side impact sensor B-pillar (left side restraints sensor 1)
- Passenger first row side impact sensor B-pillar (right side restraints sensor 1)
- Driver second row side impact sensor B-pillar (left side restraints sensor 2)
- Passenger second row side impact sensor B-pillar (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 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 air bag module(s), safety canopies, adaptive load limiting retractors and/or safety belt buckle pretensioner(s).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 sends voltage and current to the safety canopies, safety belt pretensioner(s) and/or adaptive load limiting retractors.During a frontal or side crash, the RCM may deploy the following SRS components, based on crash severity and conditions.
- 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, 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 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) will prove out by lighting for 6 seconds and then turn off.
- will flash and/or illuminate based on the message the IC receives from the RCM.
- will illuminate if the IC 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, see - Procedures.
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.
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. See Communications Network for additional information about the HS-CAN.
Occupant Classification Sensor (OCS) System
The OCS system is found only on the front passenger seat. The OCS system is comprised of a silicone gel-filled bladder mounted in 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, is sensed by the OCS system pressure sensor, then electronically communicated to the OCSM. Based on preprogrammed set points, the OCSM will inform the restraints control module (RCM), via a high-speed controller area network (HS-CAN), of the necessary information.
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.
The OCS system also interprets a variable voltage signal provided by the safety belt tension sensor to identify the presence of a cinched child safety seat in the front outboard passenger seat installed according to manufacturer instructions. The OCSM then communicates with the RCM, automatically deactivating the passenger air bag module.
The OCS system is also used for operation of the passenger Belt-Minder(R). To deactivate or reactivate the passenger Belt-Minder(R) feature, see (R) Belt-Minder (R) Deactivating/Activating or the Owner's Literature.
When an OCS system fault is present, the air bag warning indicator lamp will illuminate or the air bag warning chime will be activated (if an air bag warning indicator fault is present). The SRS then defaults the passenger air bag module to ON (activated) regardless of the size of the occupant in the front outboard passenger seat.
The OCS system components (seat cushion foam pad, bladder with pressure sensor, seat wiring harness and OCSM) are calibrated to each other and are serviced as an assembly. OCS system components are not to be installed separately.
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 system.
The safety BTS is used by the OCS system to identify the presence of a child safety seat on the front passenger seat. The safety 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 safety 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 lit 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 unlit when the passenger air bag module is enabled.
When the ignition is in the ON 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 to the front occupants correct functional operation of the PAD indicator.
When an OCS system fault is present, the SRS defaults the passenger air bag module to enabled regardless of the size of the occupant in the front outboard passenger seat. The PAD indicator will be unlit. See - Occupant Classification Sensor - Original Equipment Removal/Installation or - Occupant Classification Sensor - Service Kit Removal/Installation.
The following table indicates the passenger air bag status and the PAD indicator status based the size of the front outboard 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.
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 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.
CAUTION: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 carried out. See Programmable Module Installation (PMI).
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 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 to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IC will prove out the air bag warning indicator by lighting for 6 seconds. If no faults are detected by the RCM the IC 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 instrument cluster to turn the air bag warning indicator on and it will remain on for the rest of the key cycle. If the RCM requests illumination of the air bag warning indicator and the air bag warning indicator does not function, the IC 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 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 supplies current to the safety belt buckle switch. Current flows through the switch, buckled or unbuckled to ground. The RCM will sense the difference in this current draw, approximately 6 mA (unbuckled) or 15 mA (buckled), and use this information in determining the deployment rate of the dual-stage driver and passenger air bag modules. If the RCM detects current out of this range, it will set a DTC.
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.
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 Module
WARNING:Anytime the safety canopy 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 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 modules for vehicles with a moon roof and vehicles without a moon roof. The safety canopy modules are NOT interchangeable. If installing a new safety canopy module, the correct safety canopy module MUST be installed for the vehicle application.
The safety canopy 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.
The RCM supplies current to the seat track position sensor. Current flows through the switch, both in the forward or rearward seat positions to ground. The RCM will sense the difference in this current draw, approximately 6 mA (forward) or 15 mA (rearward), and uses this information in determining the deployment rate of the dual-stage driver air bag module. If the RCM detects current out of range, it will set a DTC.
Secondary Air Bag Warning (Chime)
The secondary air bag warning chime, is an audible chime controlled by the IC. If a fault is detected with the air bag warning indicator, a DTC is stored in the memory of the IC. Upon receiving the message from the RCM that a SRS fault has been detected, the IC sounds 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, working in conjunction with the head protection provided by a safety canopy module.
The side air bag module:
- deploys 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 safety canopy module.