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:
- Front impact severity sensor
- Driver and passenger front door side impact sensors (if equipped)
- Driver and passenger C-pillar side impact sensors (if equipped)
- Safety belt buckle switch (driver side only)
- Safing and rollover sensors internal to the RCM (if equipped)
If the RCM detects sudden vehicle deceleration and/or lateral deceleration based on information received from sensors and switches and determines that deployment is required, the RCM sends voltage and current to deploy the appropriate SRS components.
The RCM contains an internal sensor that detects vehicle rollover angles. If the RCM determines that a rollover condition exists and deployment is required, the RCM deploys the applicable SRS components.
During a frontal or side crash, the RCM may deploy the following SRS components, based on crash severity and sensor input.
- Driver and passenger safety belt retractor pretensioners
- Driver and passenger single-stage air bags (if equipped)
- Safety Canopy(R) (if equipped)
- Driver and passenger seat side air bags (if equipped)
The fact that the safety belt retractor pretensioner or air bags did not activate for both front seat occupants in a crash does not mean that something is wrong with the SRS system.
The RCM performs a self-test of the complete SRS during each startup. If an SRS 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 continuously monitors all of its SRS 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 lighting for 6 seconds and then turns off.
- flashes and/or illuminates based on the message the IPC receives from the RCM.
- illuminates if the IPC module does not receive a message from the RCM.
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 single-stage air bag, deploying upon receipt of a flow of current from the RCM.
Event Notification Signal (Gas vehicles only)
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 and fuel pump control module allows the PCM to initiate fuel cut-off to disable the fuel system in the event of a crash.
The RCM does not monitor the event notification signal circuit faults and will not set a DTC if a fault occurs.
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 Module Communications Network Testing and Inspection for information about the HS-CAN.
Impact Sensors
For this vehicle, the SRS uses as many as 5 satellite sensors in addition to the RCM, depending upon cab configuration. The RCM is mounted to the center tunnel beneath the floor console or 20 percent seat, depending on seating configuration. All vehicles have 1 front impact severity sensor located in the front of the vehicle. The first row impact sensors (if equipped) are pressure sensors mounted to each front door behind the trim panel. The second row sensors (if equipped, SuperCab and Crew Cab vehicles only) are acceleration-based sensors located on each C-pillar. Mounting orientation is critical for correct operation of all impact sensors.
Vehicles that are not equipped with seat side air bags and the Safety Canopy(R) do not have any side-impact sensors in the front door or C-pillar.
Passenger Air Bag Deactivation (PAD) Switch and Indicator (Regular cab and SuperCab vehicles only)
The Passenger Air Bag Deactivation (PAD) switch allows the passenger air bag deployment circuit to be disabled using the ignition key. The RCM then controls the state of the PAD indicator based on information provided by the PAD switch. The PAD indicator illuminates to indicate the passenger air bag module is disabled, and is off when the passenger air bag module is enabled.
The RCM briefly activates the PAD indicator to prove-out the indicator function and verify correct functional operation of the PAD indicator.
Passenger Air Bag Module
The passenger air bag module is a single-stage air bag, deploying upon receipt of a flow of current from the RCM.
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.
The RCM carries out the following functions:
- Deploys the air bag(s)/Safety Canopy(R) in the event of a deployable collision
- Activates the retractor pretensioners to control the tension of the safety belts in the event of a crash
- Monitors the SRS for faults
- Sends a message to the IPC to illuminate the air bag warning indicator if a fault is detected
The RCM monitors the SRS for possible faults. If a fault is detected, the RCM requests the IPC to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IPC proves out the air bag warning indicator by lighting for 6 seconds. If no faults are detected by the RCM, the IPC turns the air bag warning indicator off and it remains off. If the RCM detects a fault, it sends a message to the IPC to turn the air bag warning indicator on and it remains on for the rest of the ignition cycle. If the RCM requests illumination of the air bag warning indicator and the air bag warning indicator does not function, the IPC automatically activates an audible chime.
The RCM 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.
If a new RCM is installed on vehicles equipped with Roll Stability Control (RSC(R)) or trailer sway control, the IVD initialization sequence must be carried out using the scan tool. Failure to carry out the IVD initialization sequence will result in DTCs being set in the ABS module.
Driver Safety Belt Buckle Switch
The driver safety belt buckle switch indicates to the RCM whether the safety belts are buckled or unbuckled.
The RCM also communicates the driver safety belt buckle switch status to the IPC, which monitors the information to control the safety belt warning indicator. For information on the safety belt warning indicator, refer to Instrumentation, Message Center, and Warning Chimes Testing and Inspection.
Safety Belt Retractor Pretensioner
The safety belt retractor pretensioner removes excess slack from the safety belt webbing. The pretensioner is activated by the RCM when the module detects a crash event force exceeding a programmed limit.
Safety Canopy(R) Module (if equipped)
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:
- deploys upon receiving a flow of current from the RCM, initiated by the RCM.
- is mounted above the headliner.
- attaches from the A-pillar frame to the B- or C-pillar frame, depending upon cab configuration.
Seat Side Air Bag Module (if equipped)
The side air bag module:
- deploys upon receiving a flow of current from the RCM, initiated by the RCM.
- is mounted in the seat backrest.
- is used in conjunction with a Safety Canopy(R) module.
Secondary Air Bag Warning (Chime)
The secondary air bag warning chime is an audible chime located in and controlled by the IPC. If a fault is detected with the air bag warning indicator, a DTC is stored in memory of the IPC. Upon receiving the message from the RCM that a SRS fault has been detected, the IPC sounds the secondary air bag warning chime in a pattern of 5 sets of 5 beeps.