Air Bag Systems: Description and Operation

AIR BAG AND SAFETY BELT PRETENSIONER SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS) Components (Illustration 1 Of 2):

Air Bag and Safety Belf Pretensioner Supplemental Restraint System (SRS) Components (Illustration 2 Of 2):

The air bag supplemental restraint system (SRS) is designed to provide increased collision protection for front seat occupants in addition to that provided by the 3-point safety belt system. The SRS will also provide increased collision protection for the rear occupants when equipped with optional safety canopy modules. Safety belt use is necessary to obtain the best occupant protection and to receive the full advantage of the SRS.

This vehicle line contains dual-stage deployment (advanced restraint system) driver and front passenger air bag modules. These vehicles are also equipped with optional safety canopy modules.

Vehicles equipped with safety canopy modules are also equipped with seat side air bag modules. Safety canopy modules deploy from the headliner, protecting the first and second row outboard occupants during a side impact or if a rollover condition is detected. Seat side air bag modules deploy from the outboard front seat backrest upon a side impact.

Driver Air Bag Module

NOTE: References to the driver air bag module must not be confused with the driver seat side air bag components of the supplemental restraint system (SRS).

The driver air bag module:
- is steering wheel mounted.
- will deploy upon receiving a flow of current from the restraints control module (RCM).
- has no sub-assemblies.

Clockspring
The clockspring:
- is mounted on the steering column, behind the steering wheel.
- provides a continuous electrical path from the restraints control module (RCM) to the driver air bag module.
- the turn signal cancel-cam is part of the clockspring assembly.

Seat Side Air Bag Modules

NOTE: When installing a new seat side air bag module after deployment, refer to Seats for additional information.

When installing a new seat side air bag module without deployment, refer to Side Air Bag Module. Side Air Bag Module

A seat side air bag module provides protection of the thorax area (between the neck and abdomen) of the body, working in conjunction with the head protection provided by a safety canopy module. Vehicles equipped with seat side air bag modules will also be equipped with safety canopy modules.

The seat side air bag module:
- will deploy upon receiving a flow of current from the restraints control module (RCM) initiated by the side impact sensors and internal RCM circuitry.
- is installed as an assembly.
- is mounted in the front seat backrests.
- is used in conjunction with a safety canopy module.

Safety Canopy Module

WARNING: Anytime the safety canopy module has deployed, the headliner and all A-, B-, C- and D-pillar upper trim panels and attaching hardware must be replaced along with any other damaged components and hardware. Failure to do so can result in personal injury in the event of a safety canopy module deployment.

NOTE: If the headliner has the word "AIR BAG" embossed on it near each B-pillar, the vehicle is equipped with safety canopy modules.

The safety canopy module:
- will deploy upon receiving a flow of current from the RCM initiated by the side impact sensors and internal RCM circuitry when a side impact or vehicle rollover condition is detected.
- is installed as an assembly.
- is mounted above the headliner.
- attaches from the A-pillar frame to the D-pillar frame.
- cannot be interchanged from side to side.

Bridge Resistors
Safety canopy bridge resistors and seat side air bag bridge resistors are not used on this vehicle.

Occupant Classification Sensor

CAUTION:
- There are 3 occupant classification sensor (OCS) system service kits available for this vehicle (base seat, heated seat and climate controlled seat). Always make sure the correct OCS service kit is installed.
- It is necessary to carry out the OCS system reset when a front passenger seat cushion is disassembled, a new trim cover installed, a seat side shield removed or an OCS service kit is installed. A scan tool is used to trigger the active command to carry out the OCS system reset.
- Make sure the seat is completely assembled before carrying out the OCS system reset.
- The following precautions must be taken before carrying out the OCS system reset:
- Make sure the OCS system components are connected and no faults are present.
- Make sure the OCS system is not at a temperature below 0°C (32°F) or above 45°C (113°F) when initiating the OCS system reset process. If the vehicle has been exposed to extreme cold or hot temperatures, the vehicle must be exposed and kept at a temperature within the limits, 0°C to 45°C (32°F to 113°F) for a minimum of 30 minutes.
- Make sure nothing is present on the passenger seat before carrying out the OCS system reset and nothing is placed on the seat during the OCS system reset process.
- Make sure a minimum 8-second time period has passed after cycling the ignition switch ON before the process.

NOTE:
- For best results, the OCS system should be at or near room temperature, 10°C to 29°C (50°F to 85°F).
- If the first attempt to carry out the OCS system reset is unsuccessful, a second attempt must be made.

The 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 in the seat cushion, a pressure sensor that is mounted to the seat frame and an electronic control unit 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 OCS system electronic control unit (ECU). Based on programmed limits, the OCS electronic control module will inform the restraints control module (RCM), via a high-speed controller area network (CAN), of the necessary information. The RCM uses this information in determining if the passenger air bag module or passenger safety belt pretensioner are to be deployed in the event of a deployable collision. The RCM may also use this information to illuminate/not illuminate the passenger air bag deactivation (PAD) indicator.

When an OCS system fault is present, the air bag indicator lamp will illuminate or the air bag warning chime will be activated (if an air bag indicator fault is present). The SRS then defaults the passenger air bag module to ON (activated) regardless of the size of the occupant in the front outboard passenger seat.

The OCS system components (seat cushion foam pad, bladder with pressure sensor and electronic control unit) are calibrated to each other and are serviced as an assembly. OCS system components are not to be installed separately. If installing a new OCS system, OCS system component or seat cushion foam pad, a new OCS system service kit (seat cushion foam pad, bladder with pressure sensor and electronic control unit) must be installed as an assembly.

The OCS system also interprets a variable voltage signal provided by the safety belt tension sensor to identify the presence of a child safety seat in the front outboard passenger seat. The OCS system then communicates with the restraints control module (RCM), automatically deactivating the passenger air bag module and passenger safety belt pretensioner. Refer to Safety Belt Tension Sensor.

The OCS system is also used for operation of the passenger Belt Minder. To deactivate or reactivate the passenger Belt Minder feature, refer to Instrument Panel, Gauges and Warning Indicators or the owner's literature.

Passenger Air Bag Deactivation (pad) Indicator
The passenger air bag deactivation (PAD) indicator is a visual indicator used to inform the front seat occupants of the passenger air bag deactivation state. The PAD indicator is a stand-alone lamp installed into the vehicle instrument panel in a position visible to each front seat occupant.

The RCM controls the state of the PAD indicator through a direct hard-wire connection, based on information provided by the OCS system. The PAD indicator is ON to indicate the passenger air bag module is deactivated (OFF). Some exemptions to this are made in certain scenarios such as 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 cases the PAD indicator is OFF when the passenger air bag module is activated (ON).

When the ignition switch is in the ON position, the PAD indicator prove-out period is initiated by the RCM. The RCM briefly activates the PAD indicator to prove-out the indicator function and verify to the front occupants proper functional operation of the PAD indicator.

The PAD indicator will illuminate/not illuminate within 1.0 to 1.5 seconds of a change of state from the OCS system.

When an OCS system fault is present the SRS defaults the passenger air bag module to ON (activated) regardless of the size of the occupant in the front outboard passenger seat. The PAD indicator will be OFF.

Passenger Air Bag and PAD Indicator Status:

The table indicate the passenger air bag status and the PAD indicator status based the size of the front outboard passenger occupant.

Passenger Air Bag Module

NOTE: References to the passenger air bag module must not be confused with the passenger seat side air bag components of the supplemental restraint system (SRS).

The passenger air bag module:
- will deploy upon receiving a flow of current from the RCM initiated by the front impact severity sensor and internal RCM circuitry.
- is installed as an assembly.
- is mounted in the passenger side of the instrument panel.

Safety Belt Buckle Pretensioners
As part of the SRS, the safety belt buckles are equipped with 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 frontal impact event exceeding a programmed limit.

Safety Belt Switch

NOTE: When installing a new safety belt buckle, always make sure the correct safety belt buckle is being installed. The safety belt buckle switch connectors are keyed differently for seats with side air bags than for seats without side air bags.

As part of the SRS, the driver and passenger safety belt buckles are equipped with Hall-effect sensors. The safety belt switches indicate to the RCM whether the safety belt buckles are buckled or unbuckled. The RCM uses this information in determining the deployment rate of the dual-stage driver and passenger air bag modules.

The safety belt switches are also used for the driver safety belt warning system and the driver and passenger belt minder. Refer to Seat Belt Systems.

Safety Belt Tension Sensor
The safety belt tension sensor:
- is located at the safety belt anchor point.
- is used in conjunction with the OCS system.
- is a 3-wire Hall-effect sensor that is part of the front passenger safety belt and retractor assembly.

The safety belt tension sensor is used by the OCS system to identify the presence of a child safety seat on the front outboard passenger seat. The safety belt tension sensor senses the tension on the safety belt assembly then provides an output to the OCS system electronic control unit (ECU), indicating that the safety belt assembly is cinched. After sensing the weight applied to the seat by the occupant and using the safety belt tension sensor input, the OCS system determines how the occupant should be classified and communicates this information to the RCM. If the occupant is classified to be a child, the RCM will then automatically deactivate the passenger air bag module and passenger safety belt pretensioner.

Restraints Control Module (RCM)

WARNING:
- The restraints control module (RCM) orientation is critical for correct air bag supplemental restraint system (SRS) operation. If a vehicle equipped with an SRS system has been involved in a collision in which the center tunnel area has been damaged, inspect the mounting and bracket for deformation. If damaged, a new RCM must be installed whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting is restored to its original condition.
- 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 these instructions may result in the inadvertent deployment of the safety canopy and risk of personal injury.

CAUTION: When installing a new restraints control module (RCM), always make sure the correct RCM is being installed. The RCM 40-pin connector is keyed differently for vehicles with safety canopies and side air bags than the 40-pin connector for vehicles without safety canopies and side air bags. Do not force the 40-pin connector onto the RCM. If the connector is forced onto the RCM, damage to the RCM and/or connector will occur.

NOTE: When installing a new RCM, always make sure the correct RCM is being installed. If an incorrect RCM is installed, erroneous DTCs will result.

The RCM is mounted on the center tunnel under the instrument panel. The RCM carries out the following functions:
- supplies current flow to the inflators to deploy the air bags in the event of a deployable crash.
- supplies current flow to the inflators to deploy the safety canopies in the event of a deployable crash.
- activates the safety belt retractor pretensioners to remove slack from the safety belt.
- monitors the air bag SRS for faults.
- illuminates the air bag indicator if a fault is detected.
- flashes the air bag indicator to indicate the lamp fault code (LFC) detected.
- communicates through the data link connector (DLC) the current or historical diagnostic trouble codes (DTCs).
- signals the instrument cluster module to activate a chime if the air bag indicator is not available and another SRS fault exists.
- contains an internal safing sensor which is not serviced separately.
- records deployment event data.

The RCM monitors the SRS for possible faults. If a fault is detected while the ignition switch is in the RUN position, the RCM will illuminate the air bag indicator located in the instrument cluster.

When the ignition is cycled (turned OFF and then ON), the air bag indicator will remain lit for 6 seconds and then go out. If an SRS fault exists, the air bag indicator will then flash the LFC. The air bag indicator will flash the LFC 3 times, then it will remain illuminated for the rest of the key cycle. The RCM will also communicate the current and historical DTCs through the DLC, using a scan tool. If the air bag indicator does not function, and the system detects a fault condition, the RCM will signal the instrument cluster module to 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 indicator require repair.

LFCs are prioritized. If 2 or more faults occur at the same time, the fault having the highest priority will be displayed first. After that fault has been corrected, the next highest priority fault will be displayed.

The RCM includes a backup power supply. This feature provides sufficient current to deploy the front air bags and safety belt pretensioners in the event that the ignition circuit is damaged or lost in a collision before the RCM determines that air bag deployment is required. The backup power supply will deplete its stored energy approximately one minute after the battery ground cable is disconnected.

Electrical System
The electrical system that supports the air bag SRS:
- receives power from the battery through the ignition circuit.
- provides the electrical path from the RCM to the SRS components.
- provides the electrical ground path for the air bag indicator.
- provides the electrical path from the RCM to the DLC.
- provides the electrical ground path from the instrument cluster to the RCM.

Impact Sensors

WARNING: The restraints control module (RCM) orientation is critical for correct system operation. If a vehicle equipped with an air bag supplemental restraint system (SRS) has been involved in a collision in which the vehicle center tunnel area has been damaged, inspect the RCM mounting and bracket for deformation. If damaged, a new RCM must be installed whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting is restored to its original condition.

All vehicles will have a front impact severity sensor located behind the front radiator grille under the hood latch assembly. There are 2 side impact sensors located on each B-pillar. In addition there are 2 side impact sensors mounted near the driver and passenger C-pillars when the vehicle is equipped with driver and passenger safety canopy modules/seat side air bags. The RCM is mounted on the center tunnel under the instrument panel. Mounting orientation is critical for correct operation of all impact sensors.