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 (frontal restraints sensor)
- First row side impact sensor (mounted on inner rocker panel) (left/right side restraints sensor 1)
- Safety belt buckle switches (driver and passenger)
- Driver seat track position sensor
- Occupant Classification System Module (OCSM)

If the RCM detects sudden vehicle deceleration and/or lateral deceleration based on 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 or side crash, the RCM may deploy the following SRS components, based on crash severity and sensor input.

- Safety belt retractor pretensioner(s)
- Seat side air bag(s)
- Driver/passenger dual-stage air bag (one or both stages)

The fact that the safety belt retractor pretensioner(s) 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 Cluster (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.

Air Bag Module Second Stage Deployment Check

Because the driver and passenger front air bags each have 2 deployment stages, it is possible that Stage 1 has deployed and Stage 2 has not.

If a front air bag module has deployed, it is mandatory that the front air bag module be remotely deployed using the appropriate air bag disposal procedure.

- For information on driver air bag module and/or passenger air bag module remote deployment, refer to Pyrotechnic Device Disposal Service and Repair.

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 dual-stage air bag, upon receiving a flow of current from the RCM, deploying at 1 of 2 different rates depending upon vehicle impact severity and sensor input.

Event Notification Signal

In the event of a crash, the RCM provides an event notification signal to the fuel pump driver module(s) to disable the fuel system.

The RCM does not monitor the event notification signal circuit for 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 Description and Operation for information about the HS-CAN.


Impact Sensor

The SRS uses 3 satellite sensors in addition to the RCM. The RCM is mounted to the center tunnel beneath the console. The front impact severity sensor (frontal restraint sensor) is located in the front of the vehicle, behind the grille mounted on the radiator support. The side impact sensors are mounted on the inner rocker panels. Mounting orientation is critical for correct operation of all impact sensors.


Occupant Classification System (OCS) System

The Occupant Classification System (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 between the seat cushion foam and pan, a pressure sensor that is mounted to the seat frame and an OCSM which is also mounted to the seat frame. Pressure is applied to the OCS system 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 system pressure sensor, then electronically communicated to the OCSM. Based on pre-programmed set points, the OCSM will inform the RCM, via the 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 crash. The RCM also uses this information to illuminate/not illuminate the Passenger Air Bag Deactivation (PAD) indicator.

The OCSM monitors the OCS system for faults.

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 Safety Belt System Description and Operation. To deactivate or reactivate the passenger Belt Minder(R) feature, refer to Instrumentation, Message Center, and Warning Chimes Service and Repair or the Owner's Literature.


Belt Tension Sensor (BTS)

The Belt Tension Sensor (BTS):

- is a 3-wire Hall-effect sensor located at the safety belt anchor point and is part of the front passenger safety belt and retractor assembly.
- is used in conjunction with the OCS system.

The 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 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 RCM. If the occupant is classified as a child, the RCM will then automatically deactivate the passenger air bag module and illuminate the PAD indicator.

Passenger Air Bag Deactivation (PAD) Indicator

The Restraints Control Module (RCM) controls the state of the Passenger Air Bag Deactivation (PAD) indicator through a direct hard-wire connection, based on information provided by the OCS system. An exemption to this is 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 other cases, the PAD indicator is off when the passenger air bag module is enabled.

When the ignition is ON, the RCM briefly activates the PAD indicator to prove out the indicator function and verify to the front occupants correct functional operation of the PAD indicator.

The following table indicates the passenger air bag status and the PAD indicator status based on the size of the front passenger occupant.

Passenger Air Bag and 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 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: Carrying out Programmable Module Installation (PMI) will not enable the 911 assist option that is disabled.

The RCM carries out the following functions:

- Activates the driver, passenger and/or side air bag modules depending upon vehicle impact severity and the sensor inputs.
- Activates the driver and passenger retractor pretensioner(s) to control the tension of the driver and passenger safety belts in the event of a deployable crash
- Monitors the SRS for faults
- Sends a message to the IC module to 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 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 ignition 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. 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 Switches

The safety belt buckles are comprised of integrated circuits called Hall-effect switches. The safety belt buckle switches indicate to the 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, approximately 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 also communicates the driver safety belt buckle switch status to the IC module, 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

Safety belt retractor pretensioners are pyrotechnic devices integrated to the safety belt retractor assemblies. Safety belt retractor pretensioners control the tension of the driver and passenger safety belts in the event of a deployable crash.


Seat Track Position Sensor

The seat track position sensors are comprised of integrated circuits called Hall-effect switches. The seat track position sensors indicate to the RCM the position of the driver and passenger seat. The RCM uses this information in determining the deployment rate of the dual-stage air bag modules.


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 the 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.


Seat Side Air Bag Module

The side air bag module is mounted in the seat backrest and will deploy upon receiving a flow of current from the RCM.