Principles of Operation
Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
Principles of Operation
In a frontal collision, the front impact severity sensor detects sudden vehicle deceleration and sends an electrical signal to the Restraints Control Module (RCM). The RCM uses the information from the front impact severity sensor, safety belt buckle switches and the Occupant Classification System Module (OCSM) to determine deployment. If the RCM determines that deployment is required, the RCM sends voltage and current to the air bag module(s) and safety belt pretensioner(s).
In a side collision, the side impact sensor(s) detects sudden vehicle lateral deceleration and sends an electrical signal to the RCM. The RCM uses the information from the side impact sensor, safety belt buckle switches and the OCSM to determine deployment. If the RCM determines that deployment is required, the RCM sends voltage and current to the safety canopies, seat side air bag module(s), adaptive load limiter retractors and safety belt pretensioner(s).
The RCM contains an internal sensor that detects rollover angles of the vehicle. 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 limiter retractors.
During a frontal or side crash, the RCM may activate the adaptive load limiter retractors, safety belt pretensioners, seat side air bag(s), one or both stages of the driver/passenger dual-stage air bag based on crash severity and conditions. The fact that the safety belt buckle pretensioners, adaptive load limiter 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 Supplemental Restraint System (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 until the fault is no longer detected. 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:
- is located in the Instrument Cluster (IC) module.
- lamp and circuitry prove out is a function of the IC module. The IC module will prove out the air bag warning indicator by lighting the air bag warning indicator 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, deploying at 1 of 2 different rates depending upon impact severity.
High Speed Controller Area Network (HS-CAN)
This vehicle utilizes a communication system called a High Speed Controller Area Network (HS-CAN). Refer to Information Bus.
Impact Sensors
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.
The impact sensors provide data to the RCM for use in calculating impact severity. This is accomplished using various electrical sensors located throughout the vehicle.
For these vehicles, the SRS employs up to 7 impact sensors. One of the sensors is integral to the RCM and is not separately serviceable. The RCM is mounted on the center tunnel between the front seats. There are 2 front impact severity sensors located in the front-center of the vehicle, behind the grille. In addition, there are 4 side impact sensors. The first row side impact sensors are located in each of the front doors behind the trim panel, the second row side sensors are located on or near the base of the C-pillar. Mounting orientation is critical for correct operation of all impact sensors.
The side impact sensors are not interchangeable between the first and second row.
Occupant Classification Sensor (OCS) System
The Occupant Classification Sensor (OCS) system is found only on the front passenger seat. The front passenger OCS system is comprised of the following: 4 OCS weight sensor bolts that are mounted to each corner of the seat track and an OCSM which is mounted to the electrical bracket underneath the seat cushion pan. The OCS weight sensor bolts are only serviced with a seat track, the OCSM is serviced separately. The weight of any occupant or object on the front passenger seat is electronically communicated to the OCSM.
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.
When the front passenger seat is removed for service, the OCS System Reset must be carried out after the installation of the front passenger seat. When an OCS system component is installed new, the System Reset must be carried out after the installation of the front passenger seat. The Zero Seat Weight Test and/or System Reset must be carried out only as instructed to do so in the diagnostic/repair information. For information on the Zero Seat Weight Test and/or System Reset, refer to Occupant Classification Sensor (OCS) System Zero Seat Weight Test Component Tests and General Diagnostics or Occupant Classification Sensor (OCS) System Reset Service and Repair.
In the event of a crash that requires deployment, a new passenger seat track with OCS weight sensor bolts must be installed. Before carrying out the OCS System Reset, on-demand DTC B1231 must be cleared from the OCSM. Refer to Occupant Classification Sensor - Manual Seat Track Occupant Classification Sensor - Manual Seat Track or Occupant Classification Sensor - Power Seat Track Occupant Classification Sensor - Power Seat Track.
Belt Tension Sensor (BTS)
The safety belt tension sensor:
- is part of the front passenger safety belt retractor assembly.
- is located at the safety belt anchor point on the passenger seat.
- is used in conjunction with the OCS system.
- is a 3-wire Hall-effect sensor that is part of the front passenger safety belt and retractor assembly.
The safety belt tension sensor is used by the OCS system to identify the presence of a child safety seat on the front passenger seat. The safety belt tension sensor 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 belt tension sensor 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 PAD indicator.
Occupant Classification System Module (OCSM)
Based on programmed limits, the OCSM will inform the RCM, via a HS-CAN, of the necessary information. The RCM uses this information in determining if the passenger air bag module or passenger seat side air bag module is to be deployed in the event of a collision that requires deployment.
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.
Passenger Air Bag Deactivation (PAD) Indicator
The Passenger Air Bag Deactivation (PAD) indicator is a visual indicator used to inform the front seat occupants of the passenger air bag deactivation state. The PAD indicator is a stand-alone lamp installed into the vehicle instrument panel in a position visible to each front seat occupant.
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 illuminates 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 the passenger safety belt is unbuckled, 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 verify correct function.
When the OCSM detects a fault that causes DTC B2290 and/or B1013 to set on-demand in the OCS system, the OCSM sends a message to the RCM. Upon receiving the fault message from the OCSM, the RCM illuminates the PAD indicator indicating the passenger air bag module is disabled and sends a message to the IC module to illuminate the air bag warning indicator.
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 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 impact severity, safety belt usage and passenger seat occupant classification.
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: Prior to removal of the Restraints Control Module (RCM), it is necessary to upload module configuration information to the scan tool. This information needs to be downloaded into the new RCM once installed. Refer to Information Bus.
NOTE: When a new PCM is installed, the air bag warning indicator will illuminate when the ignition is ON. The warning indicator will remain on until PCM configuration is restored. Clear RCM DTCs.
NOTE: This vehicle may be equipped with the SYNC(R) V2 feature which contains the 911 assist option. Refer to the Owner's Literature.
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.
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 pretensioner and safety belt adaptive load limiter retractor to control tension on the safety belt in the event of a deployable collision.
- monitors the SRS for faults.
- sends a message to the IC module to flash/illuminate the air bag warning indicator if a fault is detected.
- communicates through the DLC the current or historical DTCs.
The RCM monitors the SRS for possible faults. If an SRS fault exists, the RCM sends a message to IC module to flash a coded sequence which is called a Lamp Fault Code (LFC) on the air bag warning indicator.
When the ignition is cycled (turned OFF and then ON), the IC module will prove out the air bag warning indicator by lighting for 6 seconds and then turn off. If a current SRS fault exists, the RCM requests illumination of the air bag warning indicator and will remain illuminated for the rest of the ignition cycle. The RCM will also communicate the on-demand (current) and continuous (historical) DTCs through the DLC, to the scan tool. 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.
Safety Belt Buckle Pretensioners
The driver and front passenger safety belt buckles are equipped with 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 collision event force exceeding a programmed limit.
Safety Belt Buckle Switches
The front safety belt buckles are equipped with safety belt buckle switches. The safety belt buckles are comprised of integrated circuits called a Hall-effect switch. 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, 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 uses this information in determining the deployment rate of the dual-stage driver and passenger air bag modules. The RCM also communicates the driver safety belt buckle switch status to the Instrument Cluster (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 (Adaptive Load Limiting) Retractor
This vehicle is equipped with driver and front passenger adaptive load limiter retractors. Adaptive load limiter retractors are pyrotechnic devices integrated to the driver and passenger safety belt retractor assemblies. Adaptive load limiter 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. The RCM monitors the readiness of the adaptive load limiter retractors. The RCM uses this information and all other information provided by the restraints system to determine what action is to be taken.
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:
- will deploy upon receiving a flow of current from the RCM initiated by the side impact sensors and internal RCM circuitry when a side impact or vehicle rollover condition is detected.
- is mounted above the headliner.
- attaches from the A-pillar frame to the C-pillar frame.
- cannot be interchanged from side to side.
Seat Track Position Sensor
The seat track position sensor is comprised of integrated circuits called a Hall-effect switch. The seat track position sensor indicate 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, 6 mA (forward) or 15 mA (rearward), and use 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 located in and controlled by the IC module. If the IC module has detected a fault with the air bag warning indicator, a DTC will be stored in the 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.
Seat Side Air Bag Module
A 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(R) module.
The side air bag module:
- will deploy upon receiving a flow of current from the RCM, initiated by the side impact sensor and internal RCM circuitry.
- is installed as an assembly.
- is mounted in the driver or front passenger seat backrest.
- is used in conjunction with a Safety Canopy(R) module.