The supplemental inflatable restraint (SIR) system supplements the protection offered by the occupants seat belt system. The SIR system contains several inflator modules located throughout the vehicle, i.e. steering wheel module, instrument panel (I/P) module, side impact modules and roof rail modules. In addition to inflator modules, the vehicle contains seat belt pretensioners that tighten the seat belt in the event of a collision, thus reducing the distance between the occupant and the seat belt when an inflator module is deployed. Each inflator module has a deployment loop that is controlled by the sensing and diagnostic module (SDM) mounted inside the vehicle. The SDM determines the severity of a collision with inputs from various sensor inputs located at strategic points on the vehicle. When the SDM detects a collision of sufficient force it will process the information provided by the sensors to further support air bag deployment. The SDM performs continuous diagnostic monitoring of the SIR system electrical components. Upon detection of a circuit malfunction, the SDM will set a diagnostic trouble code (DTC) and inform the driver by turning the AIR BAG indicator ON. The steering column and knee bolsters are designed to absorb energy and compress during frontal collisions in order to limit leg movement and decrease the chance of injury to the driver and passenger. After an air bag deployment, the SDM will send out a post-air message to the body control module (BCM). The BCM will unlock the doors and turn ON the emergency flashers, then turn ON the interior lights 15 seconds after receipt of this message.

An integral part of the SIR system is the passenger presence system (PPS). The PPS includes a module and several sensors for the purpose of assisting the SIR system in determining the presence and classification of an occupant in the passenger seat, and therefor the need to enable or disable the I/P inflator module.

The frontal SIR System consists of the following components:

A frontal collision of sufficient force will deploy the frontal air bags. The SDM contains a sensing device that converts vehicle velocity changes to an electrical signal. In the event of a frontal collision, the SDM receives a signal from the front sensors which assist the SDM in determining the severity of the collision. The SDM compares these signals to a value stored in memory. When the generated signals exceed the stored value, the SDM will cause current to flow through the deployment loops deploying the steering wheel inflator module, seat belt retractor pretensioners and depending on the PPS information simultaneously deploying the I/P inflator module. The SDM, I/P module, steering wheel module, steering wheel module coil, seat belt retractor pretensioner and the connecting wires makeup the frontal deployment loops. The SDM continuously monitors the deployment loops for malfunctions and turns the AIR BAG indicator ON if a fault is detected.

The inflatable restraint sensing and diagnostic module (SDM) is a microprocessor and the control center for the SIR System. The SDM has 2 fused power inputs. One fuse is for the battery voltage and the other fuse is for the ignition voltage. The SDM uses vehicle battery voltage as its main power input. The SDM then uses the vehicles serial data communication system and the ignition voltage input for enabling or disabling the SIR systems. The SDM contains internal sensors and uses multiple external sensors mounted at strategic locations on the vehicle to determine the severity of a collision. In the event of a collision, the SDM compares the signals from the internal and external sensors to a value stored in memory. When the generated signals exceed the stored value, the SDM will cause current to flow through the appropriate deployment loops to deploy the inflator modules or seat belt pretensioners. If the force of the impact is not sufficient to warrant inflator module deployment, the SDM may still deploy the seat belt pretensioners. The SDM records the SIR system status when a deployment occurs and turns the AIR BAG indicator located in the instrument panel cluster (IPC) ON. As soon as 3 distinct deployment commands (representing different events) have been issued to any seat belt pretensioner, or the SDM commands any inflator module to deploy once, the SDM needs to be replaced. The SDM performs continuous diagnostic monitoring of the SIR system electrical components and circuitry when the ignition is turned ON. If the SDM detects a malfunction, a DTC will be stored and the SDM will command the AIR BAG indicator ON, notifying the driver that a malfunction exist. In the event that ignition positive voltage is lost during a collision, the SDM maintains a 23-volt loop reserve (23 VLR) for deployment of the air bags. It is important when disabling the SIR system for servicing or rescue operations to allow the 23 VLR to dissipate, which could take up to 1 minute.

Important: The Passenger Presence System (PPS), heated seat element (if equipped), and the seat bottom foam cushion is a calibrated unit and cannot be service separately. After repairing or replacing the PPS, the system must be rezeroed in order to function properly. The seat belt tension sensor, part of the PPS, is serviced separate from the PPS and is integral to the seat belt buckle.

The PPS is used to monitor the weight of an occupant on the front outboard passenger seat and communicate the status to the sensing and diagnostic module (SDM) whether to enable or suppress the deployment of the instrument panel (I/P) module and the right front side impact module. The PPS consist of an electronic control module, silicone filled sensor pad, pressure sensor, seat belt tension sensor, wiring harness, and PASSENGER AIR BAG ON/OFF indicators. The silicone filled sensor pad is located under the passenger seat foam cushion and is connected by a hose clamped to the pressure sensor. The weight of the occupant sitting in the front passenger seat is measured as a pressure change within the bladder by the pressure sensor. The pressure sensor sends a voltage signal to the PPS module. If the pressure from the occupants weight is less than a specified value, the PPS module will send a suppress signal to the SDM to disable the I/P and the right front side impact modules. If the pressure from the occupants weight is higher than a specified value, the PPS module will send an enable signal to the SDM to enable the I/P and the right front side impact modules. The inflatable restraint seat belt tension sensor is mounted within the buckle of the passenger seat belt and provides an input to the PPS. When an infant car seat is properly restrained on the front passenger seat, the seat belt is tightly secured through the car seat. The seat belt pulls on the tension sensor and changes the voltage signal to the PPS module. When the PPS determines a child safety seat is present, it will request that the SDM suppress the deployment of the I/P module and turn the passenger air bag OFF indicator ON. In addition, the SDM may also disable the passenger side and roof rail air bags. The PPS monitors itself, including it sensors for faults and will set a DTC if a fault is detected. Using serial data communications, the PPS will notify the SDM of a fault and the SDM will suppress the deployment of the I/P module and request the instrument panel cluster (IPC) to turn ON the AIR BAG indicator located on the IPC and the passenger air bag OFF indicator. By turning ON either the ON or OFF indicators, the customer is notified of the enable/disable status.

The PASSENGER AIR BAG ON/OFF indicators is used to notify the driver and passenger when the instrument panel (I/P) and the right front air bag is enabled or disabled.

The AIR BAG indicator, located in the instrument panel cluster (IPC), is used to notify the driver of SIR malfunctions and to verify that the inflatable restraint sensing and diagnostic module (SDM) is communicating with the IPC. When the ignition is turned ON, the SDM is supplied with ignition positive voltage. The SDM requests the IPC to flash the AIR BAG indicator 7 times. While flashing the indicator, the SDM conducts tests on all SIR system components and circuits. If no malfunctions are detected, the SDM will communicate with the IPC through serial data communications to command the AIR BAG indicator OFF. The SDM provides continuous monitoring of the air bag circuits by conducting a sequence of checks. If a malfunction is detected the SDM will store a DTC and command the IPC to turn the AIR BAG indicator ON via serial data communication. The presence of a SIR system malfunction could result in non-deployment of the air bags or deployment in conditions less severe than intended. The AIR BAG indicator will remain ON until the malfunction has been repaired.

Dual stage inflator modules contain a housing, inflatable air bag, 2 initiating devices, canister of gas generating material and, in some cases, stored compressed gas. The 2 initiators are part of the frontal deployment loop. The function of the frontal deployment loops are to supply current through the steering wheel and instrument panel (I/P) modules to deploy the air bags. The steering wheel and instrument panel (I/P) modules have 2 stages of deployment which varies the amount of restraint to the occupant according to the collision severity. The inflatable restraints sensing and diagnostic module (SDM) determines whether to initiate stage 1 only or both stage 1 and stage 2 deployment. For moderate frontal collisions, the inflator modules deploy at less than full deployment (low deployment) which consists of stage 1 of the inflator module. For more severe frontal collisions, a full deployment is initiated which consists of stage 1 and stage 2 of the inflator module. The current passing through the initiators ignites the material in the canister producing a rapid generation of gas and is some cases, the release of compressed gas. The gas produced from this reaction rapidly inflates the air bag. Once the air bag is inflated, it quickly deflates through the air bag vent holes and/or the bag fabric.

Each dual stage inflator module is equipped with a shorting bar located in the connectors of the module. The shorting bar shorts the inflator module deployment loop circuitry to prevent unwanted deployment of the air bag when it is disconnected.

The steering wheel module coil is attached to the steering column and is located under the steering wheel. The steering wheel module coil consists of 2 or more current-carrying coils. The coils allow the rotation of the steering wheel while maintaining continuous electrical contact between the steering wheel module deployment loop and the steering wheel module. Two coil wires are used for each steering wheel module deployment loop. Additional coil wires are used for accessories that are attached to the steering wheel, depending on the vehicle content. The steering wheel module coil connector is located near the base of the steering column. The connector contains a shorting bar that shorts the steering wheel module coil deployment loop circuitry to prevent unwanted deployment of the steering wheel module when the connector is disconnected.

The steering wheel and column are designed to absorb energy when driver contact is made with steering wheel or inflated module. In a collision, the driver may contact the steering wheel directly or load the steering wheel and column through the inflated module. When the driver applies load to the inflator module or the steering wheel, the column will compress downward, absorbing some of the impact and helping to reduce bodily injuries to the driver. The steering wheel and column must be inspected for damages after a collision.

The front end sensor is equipped on vehicles to supplement the SIR performance. The front end sensor is an electronic sensor and is not part of the deployment loops, but instead provides an input to the inflatable restraint sensing and diagnostic module (SDM). The front end sensor can assist in determining the severity of some frontal collisions. The SDM contains a microprocessor which performs calculations using the measured accelerations and compares these calculations to a value stored in memory. When the generated calculations exceed the stored value, the SDM will cause current to flow through the deployment loops deploying the necessary air bags or pretensioners.

The seat belt retractor pretensioners contain a housing, a seat belt retractor, the seat belt webbing, an initiating device, and a canister of gas generating material. The initiator is part of the seat belt pretensioner deployment loop. When the vehicle is involved in a collision of sufficient force, the inflatable restraint sensing and diagnostic module (SDM) will cause current to flow through the deployment loops to the initiator. Current passing through the initiator ignites the material in the canister producing a rapid generation of gas and the release of compressed gas, if present. The gas produced from this reaction deploys the seat belt pretensioner and retracts the seat belt webbing, which removes slack in the seat belt.

Depending on the severity of the collision, the seat belt retractor pretensioner may deploy without the frontal inflator modules deploying, or they will deploy immediately before the frontal inflator modules deploy. As soon as 3 distinct deployment commands, representing different events, have been issued to any belt pretensioner, the SDM shall be considered to not be reusable.

Each seat belt retractor pretensioner is equipped with a shorting bar located on the connector of the pretensioner. The shorting bar shorts the seat belt pretensioner deployment loop circuitry to prevent unwanted deployment of the pretensioner when servicing the seat belt pretensioner.

The inflatable restraint wiring harness connects the inflator modules, inflatable restraint sensing and diagnostic module (SDM), sensors, deployment loops, and the serial data communication circuit together using weather-packed connectors. SIR connectors are yellow for easy identification. When repairing SIR wiring harnesses, follow the proper testing and repair procedures listed in the service manual.

The knee bolsters are designed to help restrain the lower torso of front seat occupants by absorbing the energy through the front seat occupants upper legs. In a collision, the front seat occupants legs may come in contact with the knee bolsters. The knee bolsters are designed to crush and deform, absorbing some of the impact and helping to reduce bodily injuries. The driver and passenger knee bolsters are located in the lower part of the instrument panel and must be inspected for damages after a collision.

The side SIR system consists of the following components:

The side impact modules are located in the outside portion of the front seat backs and the roof rail modules are located under the headliner extending from the front windshield pillar to the rear window pillar. The side impact modules and the roof rail modules contain a housing, inflatable air bag, initiating device, and a canister of gas generating material. The initiator is part of the side impact and roof rail module deployment loop. When a side impact of sufficient force occurs the SIS detects the impact and sends a signal to the SDM. The SDM compares the signal received from the SIS to a value stored in memory. When the generated signal exceeds the stored value, the SDM will cause current to flow through the side deployment loop deploying the side and the roof rail air bags. The SDM, side impact modules, roof rail modules and the connecting wires makeup the side deployment loops. The SDM continuously monitors the deployment loops for malfunctions and turns the AIR BAG indicator ON if a fault is present.

Each side impact and roof rail module is equipped with a shorting bar located on the connector of the module. The shorting bar shorts the side impact and roof rail modules deployment loop circuitry to prevent unwanted deployment of the air bag when servicing the inflator module.

The side impact sensor (SIS) contains a sensing device which monitors vehicle acceleration and velocity changes to detect side collisions that are severe enough to warrant air bag deployment. The SIS is not part of the deployment loop, but instead provides an input to the inflatable restraint sensing and diagnostic module (SDM). The SDM contains a microprocessor that performs calculations using the measured accelerations and compares these calculations to a value stored in memory. When the generated calculations exceed the stored value, the SDM will cause current to flow through the deployment loops deploying the side and the roof rail air bags.