Supplemental Inflatable Restraint System Description and Operation

The supplemental inflatable restraint system supplements the protection offered by the seat belts. The inflatable restraint sensing and diagnostic module determines the severity of a collision with the assistance of impact sensors located at strategic points on the vehicle. When the inflatable restraint sensing and diagnostic module detects a collision, the inflatable restraint sensing and diagnostic module will process the information provided by the sensors to further support air bag or pretensioner deployment. The inflatable restraint sensing and diagnostic module will deploy the air bags and pretensioners if it detects a collision of sufficient force. If the force of the impact is not sufficient to warrant air bag deployment, the inflatable restraint sensing and diagnostic module may still deploy the seat belt pretensioners. The inflatable restraint sensing and diagnostic module contains a sensing device that converts vehicle velocity changes to an electrical signal. The inflatable restraint sensing and diagnostic module compares these signals to values stored in memory. If the signals exceed a stored value, the inflatable restraint sensing and diagnostic module will determine the severity of the impact and either cause current to flow through the frontal deployment loops deploying the frontal air bags and pretensioners, or it will deploy the pretensioners only. The inflatable restraint sensing and diagnostic module continuously monitors the deployment loops for malfunctions and illuminates the supplemental inflatable restraint system air bag indicator if a fault is detected. The inflatable restraint sensing and diagnostic module performs continuous diagnostic monitoring of the supplemental inflatable restraint system electrical components. Upon detection of a circuit malfunction, the inflatable restraint sensing and diagnostic module will set a DTC and inform the driver by illuminating the supplemental inflatable restraint system air bag indicator. 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.

The supplemental inflatable restraint system utilizes the following components:

• Inflatable Restraint Sensing and Diagnostic Module
• Air Bag Indicator
• Air Bags
• Seat Belt Pretensioners
• Impact Sensors
• Passenger Presence Sensor
• Passenger Air Bag Indicator
• Seat Belt Indicators

Inflatable Restraint Sensing and Diagnostic Module 

The inflatable restraint sensing and diagnostic module is a microprocessor and the control center for the supplemental inflatable restraint system. The inflatable restraint sensing and diagnostic module contains internal sensors along with external impact sensors, mounted at strategic locations on the vehicle. In the event of a collision, the inflatable restraint sensing and diagnostic module compares the signals from the internal and external impact sensors to a value stored in memory. When the generated signals exceed the stored value, the inflatable restraint sensing and diagnostic module will cause current to flow through the appropriate deployment loops to deploy the air bags. The inflatable restraint sensing and diagnostic module records the supplemental inflatable restraint system status when a deployment occurs and illuminates the supplemental inflatable restraint system air bag indicator located in the instrument cluster. The inflatable restraint sensing and diagnostic module performs continuous diagnostic monitoring of the supplemental inflatable restraint system electrical components and circuitry when the ignition is turned ON. If the inflatable restraint sensing and diagnostic module detects a malfunction, a DTC will be stored and the inflatable restraint sensing and diagnostic module will request the instrument cluster to illuminate the supplemental inflatable restraint system air bag indicator, notifying the driver that a malfunction exists. In the event that ignition positive voltage is lost during a collision, the inflatable restraint sensing and diagnostic module maintains a 23 volt loop reserve for deployment of the air bags. It is important when disabling the supplemental inflatable restraint system for servicing or rescue operations to allow the 23 volt loop reserve to dissipate, which could take up to 1 minute.

Air Bag Indicator 

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

Air Bags 

The vehicle will contain a number of air bags, depending on vehicle available and optional equipment:

• Steering wheel
• Instrument panel
• Driver side (seat)
• Passenger side (seat)
• Driver side (B-pillar)
• Passenger side (B-pillar)
• Driver side (C-pillar)
• Passenger side (C-pillar)
• Driver knee
• Passenger knee
• Left roof rail
• Right roof rail

To view the locations of the air bags refer to: Master Electrical Component List .

Air bags contain a housing, inflatable air bag, an initiating device, a canister of gas generating material and, in some cases, stored compressed gas. Each air bag has a discrete deployment loop to supply current and deploy the air bag. The current passing through the air bags ignite 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 deflates through the air bag vent holes and/or the bag fabric. A shorting bar (if equipped) is located in the connector.

For the steering wheel and instrument panel air bag, it may be a single-stage or a dual-stage design. A single-stage design utilizes a single initiating device and will deploy at the same restraint regardless of impact severity. A dual-stage design uses two stages of deployment, which varies the amount of restraint to the occupant according to the collision severity. For moderate frontal collisions, the air bag deploys at less than full deployment which consists of stage 1 of the air bag. During a more severe frontal collision, a full deployment is initiated which consists of stage 1 and stage 2 of the air bag.

Seat Belt Pretensioners 

The vehicle will contain a number of seat belt pretensioners, depending on vehicle available and optional equipment:

• Driver - Seat belt anchor
• Driver - Seat belt retractor
• Passenger - Seat belt anchor
• Passenger - Seat belt retractor

To view the locations of the seat belt pretensioners refer to: Master Electrical Component List .

The seat belt pretensioner consists of a housing, seat belt retractor or anchor, seat belt webbing, an initiator, and a canister of gas generating materials. 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 causes current to flow through the seat belt deployment loops to the initiator. Current passing through the initiator ignites the material in the canister producing a rapid generation of gas. The gas produced from this reaction deploys the seat belt pretensioners which removes all of the slack in the seat belts. Depending on the severity of the collision, the seat belt pretensioners may deploy without the frontal air bags deploying, or they will deploy immediately before the frontal air bags deploy. A shorting bar (if equipped) is located in the connector.

Impact Sensors 

The vehicle will contain a number of impact sensors, depending on vehicle available and optional equipment:

• Front
• Door
• B-pillar
• C-pillar

To view the locations of the impact sensors refer to: Master Electrical Component List .

The impact sensors contain a sensing device which monitors vehicle acceleration to detect collisions that are severe enough to warrant air bag deployment. The front door impact sensors contain a sensing device which monitors the door cavity air pressure change to detect side collisions that are severe enough to warrant air bag deployment. It is important when working on components in the door to make sure any items which have a sealing impact on the door (water deflector, exterior door handle, speaker, door harness grommet, or sealing strip) are securely fastened when reinstalled. The impact sensors are not part of the deployment loop, but instead provide input to the inflatable restraint sensing and diagnostic module. The Inflatable Restraint Sensing and Diagnostic Module contains a microprocessor that performs calculations using the measured inputs from acceleration and pressure sensors. When the generated calculations exceed the stored value, the Inflatable Restraint Sensing and Diagnostic Module will cause current to flow through the deployment loops deploying the appropriate air bags.

Passenger Presence Sensor 

The passenger presence system is used to monitor the type of occupant that is sitting in the front passenger seat and communicate the status to the inflatable restraint sensing and diagnostic module. The inflatable restraint sensing and diagnostic module then uses this information to determine whether to enable or suppress the deployment of the passenger instrument panel air bag. The passenger presence system consists of an electronic control module, a sensor mat in the seat, a harness, and passenger air bag ON/OFF indicators.

The passenger presence sensor may be of a different type, depending on vehicle available and optional equipment:

• Capacitance mat - Transmits and receives a low-level electric field. The measured capacitance value of this field is used to determine the type of occupant sitting in the front passenger seat.
• Electrical pressure mat - A number of electrical pressure sensors determine the type of occupant sitting in the front passenger seat.
• Fluid pressure mat - A fluid-filled mat exerts pressure on a remote pressure sensor to determine the type of occupant sitting in the front passenger seat.
• Pressure switch - A pressure sensor determines if an occupant is sitting in the front passenger seat.

The passenger presence system utilizes the passenger presence sensor to determine the type of occupant sitting in the front passenger seat. In some lower featured systems, the passenger presence sensor only determines if an occupant is in the passenger seat, not the occupant type. If an occupant is not detected or the occupant type is not suitable for air bag deployment, the passenger presence sensor will send a serial data signal to the inflatable restraint sensing and diagnostic module to disable the passenger instrument panel air bag. If a suitable occupant is detected, the passenger presence sensor will send a serial data signal to the inflatable restraint sensing and diagnostic module to enable the passenger instrument panel air bag. The inflatable restraint sensing and diagnostic module will notify the customer of the enable/disable status by illuminating one of the passenger air bag ON/OFF indicator. The passenger presence system monitors itself for faults and will displays diagnostic trouble codes (DTCs) on the scan tool. When a fault is detected, the passenger presence module sends out a message to the inflatable restraint sensing and diagnostic module. The inflatable restraint sensing and diagnostic module responds by sending a command message to the instrument cluster to illuminate the supplemental inflatable restraint system air bag indicator.

Passenger Air Bag Indicator 

The passenger air bag indicator identifies the status of the instrument panel air bag. If an occupant is not detected in the passenger seat or the occupant type is not suitable for air bag deployment, the inflatable restraint sensing and diagnostic module will illuminate the passenger air bag OFF indicator. If an occupant is detected in the passenger seat, the inflatable restraint sensing and diagnostic module will illuminate the passenger air bag ON indicator.

Seat Belt Indicators 

The seat belt indicators are controlled by the inflatable restraint sensing and diagnostic module. For further information on seat belt indicators refer to: Seat Belt System Description and Operation .