Air Bag Systems: Description and Operation
Supplemental Restraint System (SRS)
Component Location
Safety Belt System Pretensioners and Inflatable Belts
SRS (Supplemental Restraint System) Deployable Devices
SRS (Supplemental Restraint System) Sensors and Indicator
Overview
The RCM (Restraints Control Module) continually receives and monitors inputs from the OCSM (Occupant Classification System Module) and various other hardwired switches and sensors. If the RCM (Restraints Control Module) detects a sudden vehicle deceleration and/or lateral deceleration based on the information received from the various sensors, and determines that deployment is necessary, the RCM (Restraints Control Module) applies voltage and current to deploy the appropriate SRS (Supplemental Restraint System) components.
System Operation
System Diagram - Supplemental Restraint System (SRS)
Network Message Chart - Supplemental Restraint System (SRS)
Module Network Input Messages - RCM (Restraints Control Module)
System Diagram - Occupant Classification System (OCS)
Network Message Chart - Occupant Classification System (OCS)
Module Network Input Messages - OCSM (Occupant Classification System Module)
Supplemental Restraint System (SRS)
The SRS (Supplemental Restraint System) is controlled by the RCM (Restraints Control Module), which continually monitors various inputs. When these inputs indicate a frontal or side crash, the RCM (Restraints Control Module) may deploy some components, based upon the severity of the crash and the sensor inputs. REFER to System Diagram - Supplemental Restraint System (SRS) to view the SRS (Supplemental Restraint System) inputs and outputs.
Although some deployable devices may not have activated for all occupants during a crash, it does not mean that something is wrong with the SRS (Supplemental Restraint System).
The RCM (Restraints Control Module) performs a self-test of the complete SRS (Supplemental Restraint System) during each startup. During normal operation, the IPC (Instrument Panel Cluster) illuminates the air bag warning indicator continuously for 6 seconds. If the SRS (Supplemental Restraint System) is free of faults, the air bag warning indicator turns off and remains off. If a SRS (Supplemental Restraint System) fault exists, the air bag warning indicator illuminates and remains illuminated for the rest of the ignition cycle. The RCM (Restraints Control Module) communicates to the IPC (Instrument Panel Cluster) via the HS-CAN (High Speed Controller Area Network). The IPC (Instrument Panel Cluster) illuminates the air bag warning indicator based on messaging from the RCM (Restraints Control Module) or if there is no communication between the RCM (Restraints Control Module) and IPC (Instrument Panel Cluster). 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 Module Second Stage Deployment Check
The driver and passenger front air bags each have 2 deployment stages. After an air bag module deployment, it is possible that stage 1 has deployed and stage 2 has not. If a front air bag module has deployed, the front air bag module must 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.
Air Bag Warning Indicator
The air bag warning indicator:
- is located in the IPC (Instrument Panel Cluster) and proves out by lighting for 6 seconds and then turning off.
- flashes and/or illuminates based on the message that 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).
Event Notification Signal
The purpose of the 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 (Powertrain Control Module) to initiate fuel cut-off to disable the fuel system in the event of a crash.
OCS (Occupant Classification System)
The OCS (Occupant Classification System) is found only on the front passenger seat. The OCS (Occupant Classification System) classifies the size of the front passenger seat occupant and provides this information to the RCM (Restraints Control Module). The RCM (Restraints Control Module) uses this information (and other inputs) in determining the deployment strategy of the passenger air bag, adaptive load limiter, and passenger seat side air bag and pretensioners. The OCS (Occupant Classification System) is comprised of:
- a silicone gel-filled bladder mounted between the seat cushion foam and seat pan
- an OCSM (Occupant Classification System Module) with an integrated pressure sensor, attached to the seat frame
- a BTS (Belt Tension Sensor), which is hard-wired to the OCSM (Occupant Classification System Module)
Pressure is applied to the OCS (Occupant Classification System) bladder when weight of any occupant or object in the front passenger seat is present. The pressure is then transferred through a tube and sensed by the OCS (Occupant Classification System) pressure sensor within the OCSM (Occupant Classification System Module). The OCSM (Occupant Classification System Module) and pressure sensor is mounted to a bracket underneath the seat cushion pan and is serviced as a kit with the seat cushion and heater mat (if equipped). The OCSM (Occupant Classification System Module) sends information concerning the weight of any occupant or object on the front passenger seat to the RCM (Restraints Control Module) via the HS-CAN (High Speed Controller Area Network). The RCM (Restraints Control Module) uses this information when determining if the passenger air bag module needs to be deployed in the event of a crash.
The OCS (Occupant Classification System) is also used for operation of the passenger Belt-Minder(R) . For additional information on the passenger Belt-Minder(R) feature, REFER to Belt-Minder(R) Safety Belt System - 1st Row. To deactivate or reactivate the passenger Belt-Minder(R) feature, REFER to Belt-Minder Deactivating and Activating Testing and Inspection or the Owner's Literature.
PAD (Passenger Air Bag Deactivation) Indicator
The RCM (Restraints Control Module) controls the state of the PAD (Passenger Air Bag Deactivation) indicator via the HS-CAN (High Speed Controller Area Network) and I-CAN (Infotainment Controller Area Network). The PAD (Passenger Air Bag Deactivation) indicator state is based on information that the OCS (Occupant Classification System) provides to the RCM (Restraints Control Module). When the passenger air bag is activated, the PAD (Passenger Air Bag Deactivation) displays ON. If the RCM (Restraints Control Module) has deactivated the passenger air bag, the PAD (Passenger Air Bag Deactivation) indicator displays OFF.
The RCM (Restraints Control Module) briefly activates the PAD (Passenger Air Bag Deactivation) indicator to prove out the indicator function and verify proper functional operation of the PAD (Passenger Air Bag Deactivation) indicator to the front occupants.
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.
Inflatable Safety Belts (if equipped)
REFER to System Operation Safety Belt System - 2nd Row.
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 (Diagnostic Trouble Code) is stored in memory of the IPC (Instrument Panel Cluster). 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.
SOS Post-Crash Alert System(TM)
The SOS Post-Crash Alert System(TM) is a system that is controlled by the BCM (Body Control Module) but initiated by the RCM (Restraints Control Module).
When a deployment event occurs, the RCM (Restraints Control Module) sends a message on the HS-CAN (High Speed Controller Area Network) to the BCM (Body Control Module). The BCM (Body Control Module) flashes the turn signal lamps and sound the horn until it is turned off. For additional information about the SOS Post-Crash Alert System(TM) , REFER to Post Crash Alert Function Description and Operation.
Component Description
Clockspring
The clockspring allows for continuous electrical connections between the driver air bag module and the RCM (Restraints Control Module). A spiral-wound cable wraps around the center of the clockspring and as the steering wheel is turned, the spiral cable inside expands or contracts in diameter as the 2 halves of the clockspring turn.
Driver Air Bag Module
The driver air bag module is a dual-stage air bag. Upon receiving a flow of current, it deploys at 1 of 2 different rates, depending upon vehicle impact severity and sensor input.
Seat Position Sensor
The seat position sensor is a Hall-effect sensor which indicates the position of the seat along the seat track. The sensor detects the presence of a shunt bracket on the track, indicating that the seat has moved past a certain point in the range of adjustment.
Occupant Classification System (OCS)
The OCS (Occupant Classification System) is found only on the front passenger seat. The OCS (Occupant Classification System) classifies the size of front passenger seat occupant.
The OCS (Occupant Classification System) is comprised of a silicone gel-filled bladder mounted between the seat cushion foam and pan, an OCSM (Occupant Classification System Module) which is mounted to the seat frame, and a pressure sensor that is internal to the OCSM (Occupant Classification System Module). Pressure is applied to the OCS (Occupant Classification System) bladder when weight of any occupant or object in the front passenger seat is present. The pressure is then transferred through a tube and sensed by the OCS (Occupant Classification System) pressure sensor and OCSM (Occupant Classification System Module). The components of an OCS (Occupant Classification System) bladder system (bladder, tube, and OCSM (Occupant Classification System Module) with integrated pressure sensor) are serviced as an assembly, and the OCS (Occupant Classification System) bladder system is serviced as a kit with the seat cushion and seat heater mat (if applicable).
The BTS (Belt Tension Sensor) is a Hall-effect sensor that modifies a reference voltage supplied by the OCSM (Occupant Classification System Module). As the amount of tension applied to the belt varies, so does the voltage that returns to the OCSM (Occupant Classification System Module).
Safety Canopy 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.
The Safety Canopy(R) module is a single-stage air bag which is designed to protect the vehicle occupant(s) during certain side impact or rollover crashes. It deploys upon receipt of current flow, in conjunction with the seat side air bag module.
Passenger Air Bag Deactivation (PAD) Indicator
The PAD (Passenger Air Bag Deactivation) indicator is comprised of a pair of LEDs (Light-emitting Diodes) in the front of the FCIM (Front Controls Interface Module). The PAD (Passenger Air Bag Deactivation) indicator cannot be serviced separate from the FCIM (Front Controls Interface Module).
Restraints Control Module (RCM)
WARNING: Do not handle, move or change the original horizontal mounting position of the RCM (Restraints Control Module) while the RCM (Restraints Control Module) 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 RCM (Restraints Control Module) and the impact sensor (if equipped) mounting areas for deformation. If damaged, restore the mounting areas to the original production configuration. A new RCM (Restraints Control Module) 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(R) option. Refer to the Owner's Literature.
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).
The RCM (Restraints Control Module) requires PMI (Programmable Module Installation) when being replaced. Refer to the scan tool instructions to carry out PMI (Programmable Module Installation). Module Configuration
For additional information about RCM (Restraints Control Module) operation, REFER to System Operation.
Inflatable Safety Belt
REFER to Safety Belt Retractor - Inflatable Safety Belt Safety Belt System - 2nd Row.
Front Impact Severity Sensor
The front impact severity sensors measure acceleration (g-rate) and are hardwired to the RCM (Restraints Control Module). Mounting orientation is critical for correct operation of the front impact severity sensors.
Side Impact Sensor - Front Door
The front door side impact sensors measure air pressure within the door in order to detect certain crashes, such as a side impact. Mounting position and orientation is critical for correct operation of the front door side impact sensors.
Safety Belt Retractor and Pretensioner
REFER to Safety Belt Retractor and Pretensioner Safety Belt System - 1st Row.
Safety Belt Retractor and Adaptive Load Limiter
REFER to Safety Belt Retractor Adaptive Load Limiter Safety Belt System - 1st Row.
Safety Belt Tension Sensor
The BTS (Belt Tension Sensor) is a 3-wire Hall-effect sensor that is part of the front passenger safety belt anchor and cannot be serviced separately from the front passenger safety belt and retractor assembly.
Safety Belt Buckle Sensor
The safety belt buckles contain integrated sensors that are Hall-effect switches. The safety belt buckle sensors are serviced as one component with the safety belt buckle.
Passenger Air Bag Module
The passenger air bag module is a dual-stage air bag which deploys at 1 of 2 different rates depending upon vehicle impact severity and sensor input.
Side Air Bag Module
The side air bag module is a single-stage air bag which deploys upon receiving current flow. It is used in conjunction with the Safety Canopy(R) module.
Side Impact Sensor - Second Row
The second row side impact severity sensors measure acceleration (g-rate), and are hardwired to the RCM (Restraints Control Module). Mounting orientation is critical for correct operation of the second row side impact severity sensors.
Safety Belt Buckle and Pretensioner
REFER to Safety Belt Buckle and Pretensioner Safety Belt System - 1st Row.
Safety Belt Inflator
REFER to Safety Belt Inflator Safety Belt System - 2nd Row.