Chevrolet Equinox Service Manual: Supplemental Inflatable Restraint System Description and Operation Restraints Control

SIR System Overview

The supplemental inflatable restraint (SIR) system supplements the protection offeredby the seat belts. The SIR system contains an inflatable restraint sensing and diagnosticmodule (SDM), air bags, seat belt pretensioners (anchor and retractor), and impactsensors. The inflatable restraint sensing and diagnostic module determines the severityof a collision with the assistance of impact sensors located at strategic points onthe vehicle.When the inflatable restraint sensing and diagnostic module detects a collision, theinflatable restraint sensing and diagnostic module will process the information providedby the sensors to further support air bag or pretensioner deployment. The inflatablerestraint sensing and diagnostic module will deploy the air bags and pretensionersif it detects a collision of sufficient force. If the force of the impact is not sufficientto warrantair bag deployment, the inflatable restraint sensing and diagnostic module may stilldeploy the seat belt pretensioners. The inflatable restraint sensing and diagnosticmodule contains a sensing device that converts vehicle velocity changes to an electricalsignal. The inflatable restraint sensing and diagnostic module compares these signalsto values stored in memory. If the signals exceed a stored value, the inflatable restraintsensing anddiagnostic module will determine the severity of the impact and either cause currentto 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 diagnosticmodule continuously monitors the deployment loops for malfunctions and illuminatesthe SIR system AIR BAG indicator if a fault is detected.The inflatable restraint sensinganddiagnostic module performs continuous diagnostic monitoring of the SIR system electricalcomponents. Upon detection of a circuit malfunction, the inflatable restraint sensingand diagnostic module will set a DTC and inform the driver by illuminating the SIRsystem AIR BAG indicator. The steering column and knee bolsters are designed to absorbenergy and compress during frontal collisions in order to limit leg movement and decreasethe chanceof injury to the driver and passenger.

SIR System AIR BAG Indicator

The SIR system AIR BAG indicator, located in the instrument cluster, is used to notifythe driver of SIR system malfunctions and to verify that the inflatable restraintsensing and diagnostic module is communicating with the instrument cluster. When theignition is turned ON, the inflatable restraint sensing and diagnostic module is suppliedwith ignition positive voltage. The instrument cluster will momentarily turn on theSIR systemAIR BAG indicator. While the indicator is on, the inflatable restraint sensing anddiagnostic module conducts tests on all SIR system components and circuits. If nomalfunctions are detected the inflatable restraint sensing and diagnostic module willcommunicate with the instrument cluster through the serial data circuit and commandthe SIR system AIR BAG indicator OFF. The inflatable restraint sensing and diagnosticmodule provides continuousmonitoring of the air bag circuits by conducting a sequence of checks. If a malfunctionis detected the inflatable restraint sensing and diagnostic module will store a diagnostictrouble code (DTC) and command the instrument cluster to illuminate the SIR systemAIR BAG indicator via serial data. The presence of a SIR system malfunction couldresult in non-deployment of the air bags or deployment in conditions less severe thanintended. TheSIR system AIR BAG indicator will remain ON until the malfunction has been repaired.

Inflatable Restraint Sensing and Diagnostic Module (SDM)

The inflatable restraint sensing and diagnostic module (SDM) is a microprocessor andthe control center for the supplemental inflatable restraint (SIR) system. The inflatablerestraint sensing and diagnostic module contains internal sensors along with externalimpact 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 theinternal and external impact sensors to a value stored in memory. When the generatedsignals exceed the stored value, the inflatable restraint sensing and diagnostic modulewill cause current to flow through the appropriate deployment loops to deploy theair bags. The inflatable restraint sensing and diagnostic module records the SIR systemstatus when a deployment occurs and illuminates the SIR system AIR BAG indicator locatedin the instrumentcluster. The inflatable restraint sensing and diagnostic module performs continuousdiagnostic monitoring of the SIR system electrical components and circuitry when theignition is turned ON. If the inflatable restraint sensing and diagnostic module detectsa malfunction, a DTC will be stored and the inflatable restraint sensing and diagnosticmodule will request the instrument cluster to illuminate the SIR system AIR BAG indicator,notifyingthe driver that a malfunction exists. In the event that ignition positive voltageis lost during a collision, the inflatable restraint sensing and diagnostic modulemaintains a 23-volt loop reserve for deployment of the air bags. It is important whendisabling the SIR system for servicing or rescue operations to allow the 23-volt loopreserve to dissipate, which could take up to 1-minute.

Air Bags

This vehicle contains 6 air bags. The 6 air bags are located in the steering wheel(dual air bags), instrument panel (passenger side) (dual air bags), driver side (B-pillar),passenger side (B-pillar), left roof rail, and right roof rail. To view the locationsof the air bags refer toSIR Identification Views. Air bags contain a housing, inflatable air bag, two initiating devices (if dualair bags),canister of gas generating material and, in some cases, stored compressed gas. Thedeployment loops supply current to deploy the air bags. The steering wheel and passengerinstrument panel air bag have two stages of deployment, which varies the amount ofrestraint to the occupant according to the collision severity. For moderate frontalcollisions the air bags deploy at less than full deployment which consists of stage-1of the air bag.For more severe frontal collisions a full deployment is initiated which consists ofstage-1 and stage-2 of the air bag. The current passing through the air bags ignitethe 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 inflatesthe air bag. Once the air bag is inflated it quickly deflates through the air bagvent holes and/orthe bag fabric. A shorting bar (if equipped) is located in the connector.

Seat Belt Pretensioners (Anchor and Retractor)

The seat belt pretensioners (driver and passenger) consist of a housing, seat beltretractor (located in the B-pillar), seat belt anchor (located on the floor), seatbelt webbing, an initiator, and a canister of gas generating materials. To view thelocations of the seat belt pretentioners refer toSIR Identification Views. The initiator is part of the seat belt pretensioner deployment loop. Whenthe vehicle is involved in a collision of sufficient force, the inflatable restraintsensing and diagnostic module causes current to flow through the seat belt deploymentloops to the initiator. Current passing through the initiator ignites the materialin the canister producing a rapid generation of gas. The gas produced from this reactiondeploys the seat belt pretensioners which removes all of the slack in the seat belts.Depending on theseverity of the collision, the seat belt pretensioners may deploy without the frontalair 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

This vehicle contains 6 impact sensors. The 6 impact sensors are located in the frontof the vehicle (2, left and right), and the 4 doors. To view the locations of theimpact sensors refer toSIR Identification Views. The impact sensors contain a sensing device which monitors vehicle accelerationand velocity changes to detect side collisions that are severe enough to warrant airbag deployment.The impact sensors are not part of the deployment loop, but instead provide inputto the inflatable restraint sensing and diagnostic module. The inflatable restraintsensing and diagnostic module contains a microprocessor that performs calculationsusing the measured accelerations and compares these calculations to a value storedin memory. When the generated calculations exceed the stored value, the inflatablerestraint sensing and diagnosticmodule will cause current to flow through the deployment loops deploying the appropriateair bags.

Passenger Presence Detection System and Passenger Air Bag Indicator

Note:The passenger presence system (PPS) is a calibrated unit. When replacing the assemblyall parts in the service kit must remain together. Do not mix any of the old partswith the new parts. After repairing or replacing the passenger presence system, thepreload test must be performed in order to function properly.

The passenger presence detection system (PPS) is used to monitor the type of occupantthat is sitting in the front passenger seat and communicate the status to the inflatablerestraint sensing and diagnostic module (SDM). The inflatable restraint sensing anddiagnostic module then uses this information to determine whether to enable or suppressthe deployment of the passenger instrument panel air bag. The passenger presence detectionsystem consists of an electronic control module, a sensor mat in the seat, a harness,and PASSENGER AIR BAG ON/OFF indicators. The passenger presence detection system transmitsand receives a low-level electric field. The measured capacitance value of this fieldis used to determine the type of occupant sitting in the front passenger seat. Ifthe measured capacitance is less than a calibrated value, then the passenger presencemodule will senda hard wire signal to the inflatable restraint sensing and diagnostic module to disablethe passenger instrument panel air bag. If the measured capacitance is greater thana calibrated value, then the passenger presence module will send a serial data signalto the inflatable restraint sensing and diagnostic module to enable the passengerinstrument panel air bag. The passenger presence detection system module will notifythe customer of theenable/disable status by illuminating one of the PASSENGER AIR BAG ON/OFF indicator.The passenger presence detection system monitors itself for faults and will displaysdiagnostic trouble codes (DTCs) on the scan tool. When a fault is detected, the passengerpresence module sends out a message to the inflatable restraint sensing and diagnosticmodule. The inflatable restraint sensing and diagnostic module responds by sendinga command messageto the instrument panel cluster to illuminate the SIR system AIR BAG indicator.

Seat Belt Indicators

The seat belt indicators are controlled through the inflatable restraint sensing anddiagnostic module (SDM). For further information on seat belt indicators refer toSeat Belt System Description and Operation.