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 limiting 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 limiting retractors.
During a frontal or side crash, the RCM may activate the adaptive load limiting retractors, safety belt pretensioners, seat side air bag(s) and/or 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 limiting 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. 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 Restraints Control Module (RCM).
- will illuminate if the IC module does not receive a message from the RCM.
Clockspring
The clockspring:
- is mounted on the steering column, behind the steering wheel.
- allows for continuous electrical connections between the driver air bag module and the Restraints Control Module (RCM) when the steering wheel is turned.
Driver Air Bag Module
The driver air bag module:
- is installed as an assembly.
- is a dual-stage air bag, deploying at 1 of 2 different rates depending upon impact severity.
- is mounted in the center of the steering wheel.
High Speed Controller Area Network (HS-CAN)
This vehicle utilizes a communication system called a High Speed Controller Area Network (HS-CAN).
The RCM communicates with various modules for required information about the vehicle.
Refer to Information Bus for additional information about HS-CAN.
Impact Sensors
The impact sensors provide data to the Restraints Control Module (RCM) for use in calculating impact severity. This is accomplished using various electrical sensors located throughout the vehicle.
For these vehicles, the Supplemental Restraint System (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.
Loops/Squibs
All deployable devices contain an initiating device called a squib. The squib is part of the deployment loop. Air bag/safety canopy modules can contain more than one squib, some vehicles may have up to 4 squibs in one air bag module. Squibs are referred to as loops during the diagnostic process.
Occupant Classification Sensor (OCS) System
The Occupant Classification Sensor (OCS) system is found only on the front passenger seat. The front passenger seat OCS system is comprised of a silicone gel-filled bladder mounted in the seat cushion, a pressure sensor that is mounted to the seat frame and a Occupant Classification System Module (OCSM) which is also mounted to the seat frame. Pressure is applied to the OCS bladder when weight of any occupant or object in the front passenger seat is present. The pressure is then transferred through a tube, is sensed by the OCS pressure sensor, then electronically communicated to the OCSM. Based on preprogrammed set points, the OCSM will inform the Restraints Control Module (RCM), via a High Speed Controller Area Network (HS-CAN), of the necessary information. The RCM uses this information in determining if the passenger air bag module is to be deployed in the event of a deployable collision. The RCM may also use this information to illuminate/not illuminate the Passenger Air Bag Deactivation (PAD) indicator. For information regarding PAD indicator operation, refer to Passenger Air Bag Deactivation Indicator.
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.
Occupant Classification System Module (OCSM)
Based on programmed limits, the Occupant Classification System Module (OCSM) will inform the Restraints Control Module (RCM), via a High Speed Controller Area Network (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 deployable collision.
The OCSM monitors the Occupant Classification Sensor (OCS) system for faults and communicates on-demand and Continuous Memory Diagnostic Trouble Codes (CMDTCs) via the Data Link Connector (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 located in the instrument panel in a position visible to each front seat occupant.
The Restraints Control Module (RCM) controls the state of the PAD indicator through a direct hardwire connection, based on information provided by the OCSM. The PAD indicator is lit to indicate the passenger air bag module is deactivated (off). Some exceptions to this are made in certain scenarios such as 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 cases, the PAD indicator is unlit when the passenger air bag module is activated (on).
When the ignition switch is in the RUN position, the PAD indicator prove-out period is initiated by the RCM. The RCM briefly activates the PAD indicator to verify operation.
When an Occupant Classification Sensor (OCS) system fault is present, the Supplemental Restraint System (SRS) defaults the passenger air bag module to on (activated) regardless of the size of the occupant in the front passenger seat. The PAD indicator will be unlit.
The following table indicates the passenger air bag status and the PAD indicator status based the size of the front 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.
- will deploy upon receiving a flow of current from the Restraints Control Module (RCM).
- is installed as an assembly.
- is mounted in the right side of the instrument panel.
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) module, it is necessary to upload module configuration information to the scan tool. This information needs to be downloaded into the new RCM module once installed. Refer to Information Bus.
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.
NOTE: When a new PCM is installed, the air bag warning indicator will illuminate when the ignition switch is ON. The warning indicator will remain on until PCM configuration is restored. Clear the Restraints Control Module (RCM) DTCs.
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 limiting retractor to control tension on the safety belt in the event of a deployable collision.
- monitors the Supplemental Restraint System (SRS) for faults.
- sends a message to the Instrument Cluster (IC) module to flash/illuminate the air bag warning indicator if a fault is detected.
- communicates through the Data Link Connector (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 the 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 CMDTCs (historical) 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
As part of the Supplemental Restraint System (SRS), 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 Restraints Control Module (RCM) when the module detects a collision event force exceeding a programmed limit.
Safety Belt Buckle Switches
As part of the Supplemental Restraint System (SRS), the front safety belt buckles are equipped with 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 Restraints Control Module (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), 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 limiting retractors. Adaptive load limiting retractors are pyrotechnic devices integrated to the driver and passenger safety belt retractor assemblies. Adaptive load limiting 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 Restraints Control Module (RCM) monitors the readiness of the adaptive load limiting retractors. The RCM uses this information and all other information provided by the restraints system to determine what action is to be taken.
Belt Tension Sensor (BTS)
The Belt Tension Sensor (BTS):
- 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 Occupant Classification Sensor (OCS) system.
- is a 3-wire Hall-effect sensor that is part of the front passenger safety belt and retractor assembly.
The safety BTS is used by the OCS system to identify the presence of a child safety seat on the front passenger seat. The BTS senses the tension on the safety belt assembly then provides an output to the Occupant Classification System Module (OCSM), indicating that the safety belt assembly is cinched. After sensing the weight applied to the seat by the occupant and using the BTS input, the OCSM determines how the occupant should be classified and communicates this information to the Restraints Control Module (RCM). If the occupant is classified as a child, the RCM will then automatically deactivate the passenger air bag module and illuminate the Passenger Air Bag Deactivation (PAD) indicator.
Safety Canopy 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 module:
- will deploy upon receiving a flow of current from the Restraints Control Module (RCM) initiated by the side impact sensors and internal RCM circuitry when a side impact or vehicle rollover condition is detected.
- is installed as an assembly.
- is mounted above the headliner.
- attaches from the A-pillar frame to the D-pillar frame (Taurus X).
- attaches from the A-pillar frame to the C-pillar frame (Taurus and Sable).
- cannot be interchanged from side to side.
Seat Track Position Sensor
As part of the Supplemental Restraint System (SRS), the driver and front passenger seats are equipped with a seat track position sensor. The seat track position sensor is comprised of integrated circuits called Hall-effect switch. The seat track position sensor indicate to the Restraints Control Module (RCM) the position of the seat, forward or rearward. The RCM uses this information in determining the deployment rate of the dual-stage driver and passenger 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 and passenger 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 controlled by the Instrument Cluster (IC). 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 Restraints Control Module (RCM) that a Supplemental Restraint System (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.
Side Air Bag Module
A seat 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 module.
The seat side air bag module:
- will deploy upon receiving a flow of current from the Restraints Control Module (RCM), initiated by the side impact sensor and internal RCM circuitry.
- is installed as an assembly.
- is mounted in the driver or passenger seat backrest.
- is used in conjunction with a safety canopy module.