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 sensor
- Driver and passenger second row side impact sensors (C-pillar)
- Safety belt buckle switches (driver and passenger)
- Seat track position sensors (driver and passenger)
- Occupant Classification System Module (OCSM)
- Safing sensors internal to the RCM (Restraints Control Module)
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.
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 pretensioner(s)
- Safety belt load limiter (passenger side only)
- Seat side air bag(s)
- Side air curtain(s)
- Driver and passenger dual-stage air bag(s) (one or both stages)
- Driver knee air bag
The fact that the safety belt retractor pretensioner, safety belt load limiter, side air curtain, 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 start up. If a SRS (Supplemental Restraint System) fault exists, the air bag warning indicator illuminates and remains 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 Panel Cluster (IPC), proves out by illuminating for 6 seconds and then turning off.
- flashes and/or illuminates based on the message the IPC (Instrument Panel Cluster) receives from the RCM (Restraints Control Module).
- illuminates if the IPC (Instrument Panel Cluster) 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 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. Refer to Information Bus 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 consists of:
- a silicone gel-filled bladder mounted between the seat cushion foam and pan
- a pressure sensor that is mounted to the seat frame
- an OCSM (Occupant Classification System Module) 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 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) automatically deactivates the passenger air bag module and illuminates 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, hard-wired connection, based on information provided by the OCS (Occupant Classification System) system. The PAD (Passenger Air Bag Deactivation) indicator illuminates to indicate the passenger air bag module is disabled. An exception to this is when the front passenger seat is determined to be empty and 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 that the PAD (Passenger Air Bag Deactivation) indicator is operating correctly.
The following table indicates the passenger air bag and 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(R) feature which contains the 911 assist option. For additional information, refer to Owner's Literature.
The RCM (Restraints Control Module) carries out the following functions:
- deploys the air bag(s)/safety curtains in the event of a deployable collision
- activates the safety belt retractor pretensioners to remove slack from the safety belts in the event of a deployable collision
- activates the passenger retractor to control the tension of the passenger safety belt in the event of a deployable collision
- monitors the SRS (Supplemental Restraint System) for faults
- sends a message to the IPC (Instrument Panel Cluster) 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) requests the IPC (Instrument Panel Cluster) to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IPC (Instrument Panel Cluster) proves out the air bag warning indicator by illuminating it for 6 seconds. If no faults are detected by the RCM (Restraints Control Module), the IPC (Instrument Panel Cluster) turns the air bag warning indicator off and it remains off. If the RCM (Restraints Control Module) detects a fault, it sends a message to the IPC (Instrument Panel Cluster) to illuminate the air bag warning indicator and it remains illuminated 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 IPC (Instrument Panel Cluster) automatically activates 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 the ignition circuit is lost or damaged during impact. The backup power supply depletes its stored energy approximately one minute after power and/or ground has been removed from the RCM (Restraints Control Module).
Event Notification Signal
The deployment event notification signal provides 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 relay 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 contain 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 status of each safety belt buckle switch to the IPC (Instrument Panel Cluster), 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 Pretensioners
The safety belt retractor 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 Retractor
The front passenger safety belt retractor is equipped with the adaptive load limiting feature that controls the tension of the front passenger safety belt in the event of a crash. The adaptive load limiter is activated by the RCM (Restraints Control Module). The driver safety belt retractor is equipped with a non-deployable (mechanical) load limiter. The front safety belt retractor may also be referred to as a seatbelt load limiter.
Side Air Curtain Modules
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:
- deploys upon receiving a flow of current from the RCM (Restraints Control Module), initiated by the RCM (Restraints Control 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 Sensors
The seat track position sensors indicate the position of the driver and passenger seats along the seat track to the RCM (Restraints Control Module). The sensor detects the presence of a shunt bracket on the track, indicating that the seat has moved forward beyond a certain point of adjustment. The RCM (Restraints Control Module) uses seat track position sensor information to determine the deployment rate of the dual-stage driver air bag and/or passenger air bag module(s).
Secondary Air Bag Warning (Chime)
The secondary air bag warning chime is an audible chime located in and controlled by the IPC (Instrument Panel Cluster). If a fault is detected with the air bag warning indicator, a DTC is stored in IPC (Instrument Panel Cluster) memory. Upon receiving the message from the RCM (Restraints Control Module) that a SRS (Supplemental Restraint System) fault has been detected, the IPC (Instrument Panel Cluster) sounds the secondary air bag warning chime in a pattern of 5 sets of 5 beeps.
Impact Sensors
In addition to the RCM (Restraints Control Module), the SRS (Supplemental Restraint System) uses 6 satellite impact sensors. The RCM (Restraints Control Module) is mounted to the center tunnel beneath the floor console. All vehicles have 2 front impact severity sensors (frontal restraints sensor), 2 first row (front door) impact sensors (side restraints sensor 1), and 2 second row impact sensors (side restraints sensor 2). The front impact severity sensors are located in the front of the vehicle, behind the bumper. The front door impact sensors are mounted behind each front door trim panel and each second row sensor is located on each C-pillar. Mounting orientation is critical for correct operation of all impact sensors.
Seat Side Air Bag Modules
The seat side air bag module:
- deploys 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 side air curtain module.
Driver Knee Bolster Air Bag Module
The driver knee bolster air bag module is part of the steering column opening trim panel and deploys upon receiving a flow of current from the RCM (Restraints Control Module).
Fault Reporting
There are 2 types of fault reporting that can be utilized 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 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.
The RCM (Restraints Control Module) does not utilize fault PIDs for this vehicle.
Those associated fault PIDs are an extension of the information provided by the DTC and are identified by the same DTC number. Use a scan tool 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 scan tool manufacturer's instructions for the scan tool being used on how to view fault PIDs.