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 first row side impact sensor B-pillar
- Driver and passenger second row side impact sensors C-pillar
- Safety belt buckle switches (driver and passenger)
- Driver seat track position restraints sensor
- Occupant Classification System Module (OCSM)
If the RCM (Restraints Control Module) 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 (Restraints Control Module) sends voltage and current to deploy the appropriate SRS (Supplemental Restraint System) components.
The RCM (Restraints Control Module) contains an internal sensor that detects vehicle rollover angles. If the RCM (Restraints Control Module) determines that a rollover condition exists and deployment is required, the RCM (Restraints Control Module) deploys the applicable SRS (Supplemental Restraint System) components.
During a frontal or side crash, the RCM (Restraints Control Module) may deploy the following SRS (Supplemental Restraint System) components, based on crash severity and sensor input.
- Safety belt retractor(s)
- Safety belt buckle pretensioner(s)
- Safety canopies(R)
- Seat side air bag(s)
- Driver and passenger dual-stage air bag(s) (one or both stages)
The fact that the safety belt buckle pretensioners, safety belt retractor(s) or 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 (Restraints Control Module) performs a self-test of the complete SRS (Supplemental Restraint System) during each startup. If a SRS (Supplemental Restraint System) 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 (Restraints Control Module) continuously monitors all of its SRS (Supplemental Restraint System) 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 (Instrument Cluster) module receives from the RCM (Restraints Control Module).
- will illuminate if the IC (Instrument Cluster) module does not receive a message from the RCM (Restraints Control Module).
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 (Restraints Control Module) 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 (Restraints Control Module), 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 (Restraints Control Module) communicates with various modules for required information about the vehicle. for additional information about the HS-CAN (High Speed Controller Area Network).
Occupant Classification System (OCS) System
The Occupant Classification System (OCS) system is found only on the front passenger seat. The OCS (Occupant Classification System) system classifies the size of front passenger seat occupant and provides this information to the Restraints Control Module (RCM). The RCM (Restraints Control Module) uses this information (and other inputs) in determining the deployment strategy of the passenger air bag and safety belt pretensioner.
The OCS (Occupant Classification System) system is also used for operation of the passenger Belt-Minder(R). For information on the passenger Belt-Minder(R); feature, refer to Instrument Panel, Gauges and Warning Indicators or the Owner's Literature.
The OCS (Occupant Classification System) 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 (Occupant Classification System Module) which is also mounted to the seat frame. Pressure is applied to the OCS (Occupant Classification System) 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 (Occupant Classification System) system pressure sensor, then electronically communicated to the OCSM (Occupant Classification System Module). The components of an OCS (Occupant Classification System) bladder system (bladder, pressure sensor and tube, OCSM (Occupant Classification System Module)) are serviced as an assembly.
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 (Occupant Classification System) system.
The BTS (Belt Tension Sensor) is used by the OCS (Occupant Classification System) system to identify the presence of a child safety seat on the front passenger seat. The BTS (Belt Tension Sensor) senses the tension on the safety belt assembly then provides an output to the OCSM (Occupant Classification System Module), indicating that the safety belt assembly is cinched. After sensing the weight applied to the seat by the occupant and using the BTS (Belt Tension Sensor) input, the OCSM (Occupant Classification System Module) determines how the occupant should be classified and communicates this information to the RCM (Restraints Control Module). If the occupant is classified as a child, the RCM (Restraints Control Module) 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 (Restraints Control Module) controls the state of the PAD (Passenger Air Bag Deactivation) indicator through a direct hardwire connection, based on information provided by the OCS (Occupant Classification System) system. The PAD (Passenger Air Bag Deactivation) 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 (Passenger Air Bag Deactivation) indicator is off when the passenger air bag module is enabled.
The RCM (Restraints Control Module) briefly activates the PAD (Passenger Air Bag Deactivation) indicator to prove-out the indicator function and verify to the front occupants correct functional operation of the PAD (Passenger Air Bag Deactivation) indicator.
The following table indicates the passenger air bag status and the PAD (Passenger Air Bag Deactivation) 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 may be equipped with the SYNC feature which contains the 911 assist option. Refer to Owner's Literature.
The RCM (Restraints Control Module) 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(s) to control the tension of the driver and passenger safety belts in the event of a deployable collision
- Monitors the SRS (Supplemental Restraint System) for faults
- Sends a message to the IC (Instrument Cluster) module to illuminate the air bag warning indicator if a fault is detected
The RCM (Restraints Control Module) monitors the SRS (Supplemental Restraint System) for possible faults. If a fault is detected, the RCM (Restraints Control Module) will request the IC (Instrument Cluster) module to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IC (Instrument Cluster) module will prove out the air bag warning indicator by lighting for 6 seconds. If no faults are detected by the RCM (Restraints Control Module), the IC (Instrument Cluster) module will turn the air bag warning indicator off and it will remain off. If the RCM (Restraints Control Module) detects a fault, it will send a message to the IC (Instrument Cluster) module to turn the air bag warning indicator on and it will remain on for the rest of the ignition cycle. If the RCM (Restraints Control Module) requests illumination of the air bag warning indicator and the air bag warning indicator does not function, the IC (Instrument Cluster) 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 (Supplemental Restraint System) and the air bag warning indicator require repair.
The RCM (Restraints Control Module) 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 (Restraints Control Module).
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 (Restraints Control Module) 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 (Restraints Control Module) does not monitor the event notification signal circuit for 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 (Restraints Control Module) whether the safety belts are buckled or unbuckled.
The RCM (Restraints Control Module) also communicates the safety belt buckle switch statuses to the IC (Instrument Cluster) 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 remove excess slack from the safety belt webbing. The pretensioners are activated by the RCM (Restraints Control Module) when the module detects a crash event force exceeding a programmed limit.
Safety Belt Retractors
Safety belt retractors 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) Modules
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.
The Safety Canopy(R) module:
- is installed as an assembly.
- is mounted above the headliner.
- attaches from the A-pillar frame to the D-pillar frame.
Seat Track Position Sensor
The seat track position sensor indicates to the RCM (Restraints Control Module) the position of the driver seat, forward or rearward. The RCM (Restraints Control Module) 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 (Instrument Cluster) module. If a fault is detected with the air bag warning indicator, a DTC will be stored in memory of the IC (Instrument Cluster) module. Upon receiving the message from the RCM (Restraints Control Module) that a SRS (Supplemental Restraint System) fault has been detected, the IC (Instrument Cluster) 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 (Supplemental Restraint System) uses 6 satellite sensors in addition to the RCM (Restraints Control Module). The RCM (Restraints Control Module) 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 Modules
The side air bag module:
- will deploy upon receiving a flow of current from the RCM (Restraints Control Module), initiated by the side restraints sensor and internal RCM (Restraints Control Module) circuitry.
- is mounted in the seat backrest.
- is used in conjunction with a Safety Canopy(R); module.
Fault PIDs
There are 2 types of fault PIDs that can be reported by the OCSM (Occupant Classification System Module). The first type, considered conventional, has only one level of fault reporting and identifies a specific concern for a given component and points to a particular diagnostic path (for example, DTC B1317 (Battery Voltage High)). The RCM (Restraints Control Module)Does not utilize fault PIDs for this vehicle.
The second type uses a process within the software of the controller that maps the byte and bit to name a specific device and fault condition. This process is called Bit-mapping and referred to as fault PIDs in the diagnosis of the vehicle. This type does not identify the specific concern or component on the first level of fault reporting (for example, DTC B2290 (Occupant Classification System Fault)). DTC B2290 can have up to 3 specific on-demand fault PIDs (areas of concern) associated with this DTC.
Those associated fault PIDs are an extension of the information provided by the DTC and are identified by the same DTC number. A scan tool must be used to view DTCs and their fault PIDs. Once a scan tool has retrieved a DTC, use the scan tool to view the fault PIDs. In the diagnostic path, other types of PIDs are sometimes used to determine the root cause (for example, resistance or voltage PIDs).
When viewing of fault PIDs has been carried out, the scan tool can display the PIDs associated with that DTC, including the status or state that exists (on-demand [active] DTC) or existed (continuous memory [historic]) DTC. Refer to the manufacturer instructions for the scan tool being used on how to view fault PIDs.