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 sensors
- Driver and passenger C-pillar side impact sensors
- Safety belt buckle switches (driver and passenger)
- Driver seat track position sensor
- Occupant Classification System Module (OCSM)
If the RCM (Restraints Control Module) detects sudden vehicle deceleration and/or lateral deceleration based on information received from 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 pretensioner(s)
- Safety Canopy(R)
- Seat side air bag(s)
- Driver and passenger dual-stage air bags (one or both stages)
The fact that the safety belt retractor pretensioner(s) or air bags did not activate for both front seat occupants in a crash 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 Instrument Panel Cluster (IPC) 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 High Speed Controller Area Network (HS-CAN). 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 mustbe 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).
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.
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 and disable the fuel system in the event of a crash.
High Speed Controller Area Network (HS-CAN)
This vehicle utilizes a communication system called a HS-CAN (High Speed Controller Area Network). 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), refer to Information Bus.
Impact Sensors
For this vehicle, 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 located in the front of the vehicle. The first row impact sensors are mounted to each front door behind the trim panel, the second row sensors are located on each C-pillar. Mounting orientation is critical for correct operation of all impact sensors.
Occupant Classification System (OCS)
The Occupant Classification System (OCS) 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 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, passenger seat side air bag and pretensioner. The OCS (Occupant Classification System) is comprised of an OCSM (Occupant Classification System Module) and 4 OCS (Occupant Classification System) weight sensor bolts that are mounted to each corner of the seat track and can be serviced separately from the seat track. The OCSM (Occupant Classification System Module) is mounted to an electrical bracket underneath the seat cushion pan and can be serviced separately. 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 in determining if the passenger air bag module is 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 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.
Passenger Air Bag Deactivation (PAD) 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) indicator displays ON. If the RCM (Restraints Control Module) has deactivated the passenger air bag, the PAD (Passenger Air Bag Deactivation) indicator displays OFF.
When the ignition is first turned ON, the RCM (Restraints Control Module) briefly activates both the ON and OFF LEDs in the PAD (Passenger Air Bag Deactivation) indicator to prove out the indicator function and verify proper 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 seat 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.
- cannot be interchanged between Edge and MKX vehicles
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 is equipped with the SYNC(R) feature which contains the 911 assist option. Refer to the Owner's Literature.
The RCM (Restraints Control Module) carries out the following functions:
- Deploys the air bag(s)/Safety Canopy(R) in the event of a deployable crash
- Activates the safety belt retractor pretensioner(s) to remove slack from the safety belt(s) in the event of a crash
- 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) sends a request to 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 lighting 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 turn the air bag warning indicator on and it remains 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 IPC (Instrument Panel Cluster) automatically activates an audible chime.
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).
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 driver safety belt buckle switch status to the IPC (Instrument Panel Cluster), which monitors the information to control the safety belt warning indicator. For additional information about 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 Canopy(R) 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:
- deploys upon receiving a flow of current from the RCM (Restraints Control Module), initiated by the RCM (Restraints Control Module).
- is mounted above the headliner.
- attaches from the A-pillar frame to the D-pillar frame.
Seat Side Air Bag Module
The side air bag module:
- deploys upon receiving a flow of current from the RCM (Restraints Control Module), initiated by the RCM (Restraints Control Module).
- is mounted in the seat backrest.
- is used in conjunction with a Safety Canopy(R) module.
Seat Track Position Sensor
The seat track position sensor indicates to the RCM (Restraints Control Module) the position of the driver 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. The RCM (Restraints Control Module) uses this information (and other 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 IPC (Instrument Panel Cluster). If a fault is detected with the air bag warning indicator, a DTC 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.