Principles of Operation
Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
Refer to Wiring Diagram Set 46, Air Bag for schematic and connector information Diagrams By Number.
Principles of Operation
The Restraints Control Module (RCM) continuously receives/monitors inputs from the following Supplemental Restraint System (SRS) components.
- Front impact severity sensor
- Driver safety belt buckle switch
- Passenger Air Bag Deactivation (PAD) switch
If the RCM detects sudden vehicle deceleration and/or lateral deceleration based on all the information received from all sensors and switches and determines that deployment is required, the RCM sends voltage and current to deploy the appropriate SRS components.
During a frontal crash, the RCM may deploy the following SRS components, based on crash severity and sensor input.
- Safety belt buckle pretensioner(s)
- Driver and passenger single-stage air bags
The fact that the safety belt buckle pretensioners or air bags did not activate for both front seat occupants in a crash does not mean that something is wrong with the system.
The RCM performs a self-test of the complete 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:
- located in the Instrument Panel Cluster (IPC) module will prove out by lighting for 6 seconds and then turn off.
- will flash and/or illuminate based on the message the IPC module receives from the RCM.
- will illuminate 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 and will deploy depending on vehicle impact severity and sensor input.
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 information about the HS-CAN.
Passenger Air Bag Module
The passenger air bag module:
- is a single stage air bag and will deploy depending on vehicle impact severity and sensor input.
Restraints Control Module (RCM)
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 supports the 911 assist option. Refer to the Owner's Literature.
The RCM carries out the following functions:
- Activates the driver/passenger air bag modules depending upon vehicle impact severity and sensor input, in the event of a deployable collision
- Activates the safety belt buckle pretensioners to remove slack from the safety belt in the event of a deployable collision
- Monitors the SRS for faults
- Sends a message to the Instrument Panel Cluster (IPC) module to illuminate the air bag warning indicator if a fault is detected
- Communicates through the Data Link Connector (DLC) the current and/or historical DTCs
The RCM monitors the SRS for possible faults. If a fault is detected, the RCM will request the IPC module to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IPC module will prove out the air bag warning indicator by lighting for 6 seconds. If no faults are detected by the RCM the IPC module will turn the air bag warning indicator off and it will remain off. If the RCM detects a fault, it will send a message to the IPC module to turn the air bag warning indicator on and it will remain on for the rest of the key cycle. If the RCM requests illumination of the air bag warning indicator and the air bag warning indicator does not function, the IPC 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. The backup power supply will deploy the SRS components 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. The backup power supply will deplete its stored energy approximately one minute after the battery ground cable is disconnected.
The RCM will also communicate the on-demand (current) and continuous (historical) DTCs through the DLC to the scan tool.
Safety Belt Buckle Switches
The driver safety belt buckle is comprised of integrated circuits called a Hall-effect switch. The safety belt buckle switch indicates to the RCM whether the safety belt are buckled or unbuckled.
The RCM also communicates the driver safety belt buckle switch status to the IPC 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 Buckle 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 crash event force exceeding a programmed limit.
Secondary Air Bag Warning (Chime)
The secondary air bag warning chime is an audible chime located in and controlled by the IPC module. If a fault is detected with the air bags warning indicator a DTC will be stored in memory of the IPC module. Upon receiving the message from the RCM that a SRS fault has been detected, the IPC module will sound the secondary air bag warning chime in a pattern of 5 sets of 5 beeps.
Impact Sensors (Restraints Sensor)
For this vehicle line, the SRS uses one satellite sensor in addition to the RCM. The RCM is mounted beneath the driver seat. All vehicles have one front impact severity sensor located in the front-center area of the vehicle, behind the grille mounted on the radiator support. Mounting orientation is critical for correct operation of all impact sensors.
The air bag warning indicator may not illuminate to indicate a fault is present until approximately 30 seconds after the ignition switch has been turned from the OFF to the ON position. This is the time required for the RCM to complete the testing of the SRS. If the air bag warning indicator is inoperative and an SRS fault exists, a chime will sound in a pattern of 5 sets of 5 beeps. If this occurs, the air bag warning indicator will need to be repaired before diagnosis can continue.