Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)

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

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. Safety belt use is necessary to obtain the best occupant protection and to receive the full advantage of the SRS.

Before servicing the SRS, the system must be depowered.

The SRS deployable components are shown in the illustration.

Air Bag And Safety Belt Pretensioner Supplemental Restraint System (SRS) Deployable Components:

The SRS sensor components are shown in the illustration.

Air Bag And Safety Belt Pretensioner Supplemental Restraint System (SRS) Sensor Components:

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.
- is a dual-stage air bag, deploying at 1 of 2 different rates depending upon impact severity, safety belt usage and driver seat position.
- will deploy upon receiving a signal from the restraints control module (RCM).
- has no subassemblies.

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

Driver Seat Side Air Bag Module

NOTE:
- References to side air bag modules refer to the seat-mounted and not to the steering wheel- or instrument panel-mounted air bag components of the supplemental restraint system (SRS).
- When installing a new driver seat side air bag module after deployment.

The driver seat side air bag module:
- will deploy upon receiving a signal from the restraints control module (RCM) initiated by the driver side impact sensor.
- is installed as an assembly.
- is mounted in the driver seat back.

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:
- is a dual-stage air bag, deploying at 1 of 2 different rates depending upon impact severity, safety belt usage and passenger seat occupant classification (if equipped).
- is installed as an assembly.
- is mounted in the passenger side of the instrument panel.

Passenger Seat Side Air Bag Module

NOTE:
- References to side air bag modules refer to the seat-mounted and not to the steering wheel- or instrument panel-mounted air bag components of the supplemental restraint system (SRS).
- When installing a new passenger seat side air bag module after deployment.

The passenger seat side air bag module:
- will deploy upon receiving a signal from the restraints control module (RCM) initiated by the passenger side impact sensor.
- is installed as an assembly.
- is mounted in the passenger seat back.

Safety Belt Pretensioners
As part of the supplemental restraint system (SRS), the safety belt retractors are equipped with pretensioners. The belt retractor pretensioners rotate the safety belt retractors to remove excess slack from the safety belt webbing. The pretensioners are activated by the restraints control module (RCM) when the module detects a frontal impact force exceeding a programmed limit.

Deployable Steering Column
This vehicle is equipped with a deployable steering column. The deployable steering column includes a deployable device that, once deployed, reduces the amount of force necessary to collapse the steering column during a crash event. The deployable device is activated by the restraints control module (RCM) depending on when the module detects a crash event force exceeding a programmed limit and the position of the driver seat. After deployment, a new steering column must be installed.

Safety Belt Buckle Switches
The safety belt buckle switches are comprised of integrated circuits called Hall-effect sensors. The safety belt buckle switches (Hall-effect sensors) are located in the driver and passenger safety belt buckles. Safety belt buckle switches are used to indicate to the restraints control module (RCM) whether the safety belts are buckled or unbuckled. The RCM uses this information in determining the deployment rate of the dual-stage driver and passenger air bag modules.

Seat Track Position Sensor
The seat track position sensor is a Hall-effect sensor located on the driver seat track. Based on programmed limits the seat track position sensor will inform the restraints control module (RCM) of the driver seat position. The RCM uses this information in determining the deployment rate of the dual-stage driver air bag module.

Occupant Classification Sensor

CAUTION:
- It is necessary to rezero the OCS system when a front passenger seat cushion is disassembled, a new trim cover installed or an OCS service kit is installed. A diagnostic tool is used to trigger the active command to carry out rezeroing of the OCS system.
- Make sure the seat is completely assembled before rezeroing.
- The following precautions must be taken before rezeroing the OCS system:
- 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 rezeroing 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 rezeroing and nothing is placed on the seat during the rezeroing process.
- Make sure a minimum 8-second time period has passed after cycling the ignition switch ON before the rezeroing process.

NOTE:
- For best results in rezeroing, 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 rezero the OCS system is unsuccessful, a second attempt must be made.
- Occupant classification sensor (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. The OCS system components are not to be installed separately. If a new OCS system, OCS system component or seat cushion foam pad are needed, a new OCS system service kit (seat cushion foam pad, bladder with pressure sensor and electronic control unit) must be installed as an assembly.
- To identify between a production OCS system and a service OCS system (OCS service kit), inspect the electronic control unit (ECU) electrical connector. A production OCS system allows the disconnection of the ECU electrical connector. A service OCS system (OCS service kit) has the ECU electrical connector glued to the ECU, it cannot and should not be disconnected or altered. An OCS system service kit also has an in-line 18-pin connector between the OCS ECU and the seat wiring harness.
- The heated seat element on the front passenger seat cushion is not serviceable separately. If a new heated seat element is needed on the front passenger seat cushion a new occupant classification sensor (OCS) service kit and a new heated seat element must be installed.

The seat occupant classification sensor (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 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 preprogrammed set points the OCS system ECU will inform the restraints control module (RCM), via a high-speed controller area network (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 collision. The RCM also uses this information to illuminate/not illuminate the passenger air bag deactivation (PAD) indicator.

When an OCS system fault is present, the air bag warning 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 cinched child safety seat in the front outboard passenger seat installed according to manufacturer instructions. The OCS system then communicates with the restraints control module (RCM), automatically deactivating the passenger air bag module.

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.

Safety Belt Tension Sensor (BTS)
The safety belt tension sensor:
- is part of the front outboard passenger safety belt buckle assembly.
- is located on the front passenger seat track safety belt buckle mounting bracket.
- is used in conjunction with the occupant classification sensor (OCS) system.
- is a 3-wire Hall-effect sensor that is incorporated into the mounting anchor of the front outboard passenger safety belt buckle 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, when the child safety seat is installed according to manufacturer instructions. 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 restraints control module (RCM). If the occupant is classified to be a child, the RCM will then automatically deactivate the passenger air bag module.

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 restraints control module (RCM) controls the state of the PAD indicator through a direct hardwire connection, based on information provided by the occupant classification sensor (OCS) system. The PAD indicator is lit to indicate the passenger air bag module is disabled. 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 unlit when the passenger air bag module is enabled.

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 correct functional operation of the PAD indicator.

The PAD indicator will be lit/unlit 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 enabled regardless of the size of the occupant in the front outboard passenger seat. The PAD indicator will be unlit.

Passenger Air Bag And PAD Indicator Status:

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

Restraints Control Module (RCM)

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 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.

NOTE: When a new RCM is first installed in the vehicle, module configuration must be carried out. The diagnostic trouble code (DTC) B2477 will be stored in the RCM memory (continuous fault) and will flash lamp fault code (LFC) 54 (or higher priority code if one exists) on the air bag indicator. The DTC B2477 cannot be cleared from memory until RCM configuration has been carried out.

The restraints control module (RCM) is mounted on the center tunnel under the instrument panel. The RCM carries out the following functions:
- Signals the inflators to deploy the air bags 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.
- Receives information from the front and side impact sensors.
- Sends safety belt buckle status to the instrument cluster for safety belt lamp and belt-minder.
- 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 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.

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 2-digit LFC. The air bag indicator will flash the LFC 5 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 data link connector (DLC), using the diagnostic tool. If the air bag indicator does not function, and the system detects a fault condition, the RCM will signal the instrument cluster 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 backup power to deploy the air bags in the event that the ignition circuit is damaged in a collision before air bag deployment is activated. The backup power supply will deplete its stored energy approximately one minute after ignition power is removed from the RCM.

Electrical System
The electrical system that supports the air bag supplemental restraint system (SRS):
- is powered by the battery through the ignition circuit.
- provides the electrical path from the restraints control module (RCM) to the SRS components.
- provides the electrical path from the RCM to the air bag indicator.
- provides the electrical path from the RCM to the data link connector (DLC).
- provides the electrical path from the RCM to the instrument cluster.

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 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.
- Vehicle sensor orientation is critical for correct system operation. If a vehicle equipped with an air bag supplemental restraint system (SRS) is involved in a collision, inspect the sensor mounting bracket and wiring pigtail for deformation. Install and correctly position a new sensor or any other damaged supplemental restraint system (SRS) components whether or not the air bag is deployed.

For these vehicles, the SRS employs 5 impact sensors. One of the sensors is integral to the RCM and is not separately serviceable. The RCM is mounted on the center tunnel under the instrument panel. There are 2 front impact severity sensors located in the front-center of the vehicle, behind the grille. In addition there are 2 side impact sensors. The side impact sensors are located at the base of each B-pillar safety belt retractor and pretensioner. Mounting orientation is critical for correct operation of all impact sensors.