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 sensor
- Safety belt buckle switch
- Passenger Air Bag Deactivation (PAD) switch
- PAD indicator
If the RCM detects sudden vehicle 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 retractor pretensioner(s)
- Driver/passenger air bag
The fact that the safety belt retractor pretensioners or air bags did not deploy for both front seat occupants in a collision does not mean that there is a fault in the SRS.
The RCM performs a self-test of the SRS during each startup. If a SRS fault is detected, the RCM sends a message to the Instrument Cluster (IC) module to flash a coded sequence which is called a Lamp Fault Code (LFC) on the air bag warning indicator. The air bag warning indicator will flash the LFC and remain illuminated for the rest of the ignition cycle until the fault is no longer detected. In addition to the self-test at start up, the RCM continuously monitors all of its SRS components and circuitry for correct operation. If a fault is detected during continuous monitor, the air bag warning indicator will illuminate and remain illuminated until the fault is corrected.
Air Bag Warning Indicator
The air bag warning indicator:
- located in the IC module, will prove out by lighting for 6 seconds and then turn off.
- will flash and/or illuminate based on the message the IC module receives from the RCM.
- will illuminate if the IC 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 single stage.
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.
Passenger Air Bag Deactivation (PAD) Switch
The PAD switch:
- is present on regular cab and SuperCab vehicles only.
- is located on the instrument panel to the right of the climate controls.
- contains a PAD indicator that indicates when the PAD switch is activated (passenger air bag disabled).
- allows the passenger air bag deployment circuit to be disabled using the ignition key.
Passenger Air Bag Module
The passenger air bag module is single stage.
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 may be equipped with the SYNC(R) V2 feature which contains the 911 assist option. Refer to the Owner's Literature.
The RCM carries out the following functions:
- Deploys the air bag(s) in the event of a deployable collision
- Activates the safety belt 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 IC module 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 will request the IC module to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IC module will prove out the air bag warning indicator by lighting for 6 seconds. If no faults are detected by the RCM the IC 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 IC 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 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. 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 Data Link Connector (DLC) to the scan tool.
Safety Belt Buckle Switch
The safety belt buckle switch indicates to the RCM whether the driver safety belt is buckled or unbuckled.
Safety Belt Pretensioners
The safety belt retractor pretensioners remove excess slack from the safety belt webbing. The pretensioners are activated by the RCM when the module detects a collision event force exceeding a programmed limit.
Sensors, Impact
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.
For this vehicle line, the SRS uses one satellite sensor in addition to the RCM. The RCM is mounted to the center tunnel beneath the console. All vehicles have one front impact severity sensor located in the front-center area of the vehicle, behind the grille mounted on the lower radiator support. Mounting orientation is critical for correct operation of all impact sensors.
A DTC can indicate several concerns. The DTCs are to assist in system diagnosis and are not to be considered definitive. Always refer to the pinpoint test corresponding to the DTC to determine where the concern lies and to repair the concern correctly.
Lamp Fault Codes (LFCs)
When the RCM detects a system fault, it will send a message to the IC module to illuminate the air bag warning indicator and to flash a coded sequence which is called a LFC. The code is 2 digits. The first digit is flashed with a 0.5-second interval between pulses. There is a 2-second pause before the second digit is flashed, which also has a 0.5-second interval between pulses. There is a 5-second pause between each display of an LFC.
Each LFC is flashed 3 times after which the air bag indictor will remain lit for the remainder of the key-on cycle. If there are multiple LFCs, each LFC will flash in order of priority.
Secondary Air Bag Warning (Chime)
The secondary air bag warning chime is an audible chime located in and controlled by the IC module. If a fault is detected with the air bag warning indicator, a DTC will be stored in memory of the IC module. Upon receiving a message from the RCM that a 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.