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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 air bag module(s) and/or safety belt retractor pretensioner(s).

During a frontal, the RCM may deploy the following SRS components, based on crash severity and conditions.

- 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 an 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 is located in the IC module.

- The IC module will prove out the air bag warning indicator by illuminating it 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.
- The air bag warning indicator will illuminate and/or flash based on the message the IC module receives from the RCM.
- The air bag warning indicator 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 RCM when the steering wheel is turned.


Driver Air Bag Module

The driver air bag module:

- is single stage.
- is mounted in the center of the steering wheel.


High Speed Controller Area Network (HS-CAN)

This vehicle utilizes a communication system called a 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 lamp (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 installed as an assembly.
- is single stage.
- is mounted in the passenger side of the instrument panel.


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.

NOTICE: Prior to removal of the Restraints Control Module (RCM), 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. Programming and Relearning

The RCM carries out the following functions:

- Deploys the air bag(s) 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 Cluster (IC) module to illuminate the air bag warning indicator if a fault is detected
- Communicates through the DLC the current or historical DTCs

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 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.

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