Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
AIR BAG AND SAFETY BELT PRETENSIONER SUPPLEMENTAL RESTRAINT SYSTEM (SRS)Air Bag And Safety Belt Pretensioner Supplemental Restraint System (SRS) Components:
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.
This vehicle line contains dual-stage deployment (advanced restraint system) driver and front passenger air bag modules.
Driver Air Bag Module
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 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).
Passenger Air Bag Module
The passenger air bag module:
- will deploy upon receiving a flow of current from the restraints control module (RCM).
- is installed as an assembly.
- is mounted in the passenger side of the instrument panel.
Safety Belt Pretensioners
As part of the supplemental restraints system (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 restraints control module (RCM) when the module detects a frontal or side impact event exceeding a programmed limit and the safety belt is latched (buckled). The passenger safety belt pretensioner can deploy regardless of the presence of an occupant if the front outboard passenger safety belt is latched (buckled).
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 (11°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).
- To identify between a production OCS system and a OCS system service kit, inspect the OCS ECU electrical connector.
A production OCS system allows the disconnect of the electrical connector from the OCS ECU.
An OCS system service kit has the OCS ECU electrical connector glued to the ECU. It cannot and should not be disconnected or altered.
- If the first attempt to rezero the OCS system is unsuccessful, a second attempt must be made.
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 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 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 wiring harness, seat cushion frame, 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 the operation of the passenger Belt Minder.
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 proper 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 tables indicate the passenger air bag status and the PAD indicator status based on the size of the front outboard passenger occupant and the passenger safety belt buckle switch status.
Safety Belt Buckle Switch
As part of the supplemental restraint system (SRS), the driver and front outboard passenger safety belt buckles are equipped with a Hall-effect switch. The safety belt switches indicate to the restraints control module (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 Belt Minder and passenger Belt Minder (if equipped).
Safety Belt Tension Sensor
The safety belt tension sensor:
- is part of the front outboard passenger safety belt and retractor assembly.
- is located at the safety belt anchor point.
- is used in conjunction with the occupant classification sensor (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, 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.
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 area for deformation. If damaged, the RCM must be replaced 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 installing a new restraints control module (RCM), always make sure the correct RCM is being installed. If an incorrect RCM is installed, erroneous DTCs will result.
The restraints control module (RCM) is mounted on the center tunnel between the front seats. The RCM:
- supplies current flow to the inflators to deploy the air bags in the event of a deployable crash.
- activates the safety belt buckle pretensioners to remove slack from the safety belt.
- monitors the air bag supplemental restraint system (SRS) for faults.
- illuminates the air bag indicator if a fault is detected.
- illuminates the passenger air bag deactivation (PAD) indicator when conditions warrant illumination.
- 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 ON 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 DLC, using a diagnostic 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 energy to deploy the front air bags and safety belt buckle 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 supplemental restraint system (SRS):
- receives power from the battery through the ignition circuit.
- provides the electrical path from the restraints control module (RCM) to the SRS components.
- provides the electrical ground path for the air bag indicator.
- provides the electrical path from the RCM to the data link connector (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 area for deformation. If damaged, the RCM must be replaced 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 proper 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. Replace and properly position the sensor or any other damaged supplemental restraint system (SRS) components whether or not the air bag is deployed.
The RCM incorporates integral sensors that are not separately serviceable. All vehicles will have a front impact severity sensor located on the hood latch support bracket. The RCM is mounted on the center tunnel between the front seats. Mounting orientation is critical for correct operation of all impact sensors.