Air Bag Restraint System GMC Suburban I

IDENTIFICATION

Note. This article has been updated per General Motors Technical Service Bulletin 56-32-01, dated March 27, 1995.

All models equipped with a Supplemental Inflatable Restraint (SIR) system have a number "2" (driver and passenger-side air bags) or "3" (driver-side air bag only) in the seventh position of the Vehicle Identification Number (VIN). Some vehicles have the words Supplemental Inflatable Restraint or SIR on the inflator module. Steering wheel hub is slightly larger in order to accommodate the driver-side air bag.

SUPPLEMENTAL INFLATABLE RESTRAINT (SIR) SYSTEM

The Supplemental Inflatable Restraint (SIR) system is designed to protect the driver and passenger (if equipped) in a frontal collision. The air bag(s) will deploy only upon frontal or near frontal impact of no more than 30 degrees off the center line of vehicle. System is not designed to deploy in rear impacts, side impacts, or rollovers. A frontal impact of sufficient severity (comparable to a collision into a solid wall at approximately 14 MPH or more) will cause sensors in vehicle to detect this sudden deceleration. These sensors, in turn, trigger the inflator module(s).

Note. Following SIR components are not necessarily installed on all vehicles.

DIAGNOSTIC ENERGY RESERVE MODULE (DERM)

Vehicles not equipped with a Sensing and Diagnostic Module (SDM) are equipped with a DERM. DERM performs diagnostic monitoring of all system components, stores both current and past SIR system fault code information, warns driver of SIR system faults by controlling AIR BAG warning light, and records SIR system status during a vehicle accident. In addition, DERM maintains a 36-Volt Loop Reserve (36VLR) energy supply to provide sufficient deployment energy for about 2 minutes if vehicle system voltage is low or is lost in an accident.

A 24-pin connector connects DERM to SIR harness. Harness connector uses gold-plated terminals and shorting bar in terminal contact area. DERM connector also has a gold-plated shorting bar that connects AIR BAG warning input to ground when the DERM connector is disconnected. With DERM disconnected, AIR BAG warning light remains on when ignition switch is in RUN, BULB TEST, or START positions. DERM is located under or behind instrument panel.

AIR BAG RESTRAINT WARNING LIGHT

Note. Some vehicles have an INFLATABLE RESTRAINT warning light as opposed to an AIR BAG warning light.

When ignition switch is in RUN, BULB TEST, or START positions, battery voltage is applied to AIR BAG warning light. DERM/SDM illuminates this light by providing a ground to a lamp driver. Some vehicles are equipped with a Serial Data Controlled Warning Lamp (SDCWL). An SDCWL equipped vehicle utilizes a smart cluster which communicates via the serial data line, so in this case, DERM/SDM transmits a request to turn on AIR BAG warning light. When ignition is first turned on, AIR BAG warning light verifies light and DERM/SDM operation by flashing 7-9 times. Light is also used to warn driver of SIR electrical system faults which could potentially affect SIR system operation. AIR BAG warning light is the key to driver notification of SIR system faults.

In addition, the light provides diagnostic information by flashing Diagnostic Trouble Codes (DTCs) when the flash code diagnostic mode is entered on models without on-board diagnosis. INFLATABLE RESTRAINT indicator light notifies driver of SIR system faults.

ARMING SENSOR/DUAL POLE ARMING SENSOR

Arming sensor/dual pole arming sensor is a protective switch located in power feed side (positive side) of deployment loop. It is calibrated to close at low-level velocity changes (lower than discriminating sensors). This assures that each inflator module is connected directly to 36VLR output of DERM or ignition voltage when either of the discriminating sensors close.

Arming sensor/dual pole arming sensor consists of a sensing element, normally open switch contacts, a diagnostic resistor, and 2 diodes. Sensing element closes switch contacts when velocity of vehicle changes at a rate indicating potential need for deployment. A diagnostic resistor is connected in parallel with normally open switch contacts and allows for a small amount of current flow through deployment loop during normal undeployed conditions. This small current flow results in voltage drops across each component within loop.

DERM monitors these voltage drops to detect circuit or component faults. The 2 diodes provide isolation between 36VLR output of DERM and ignition voltage. In some vehicles, arming sensor is combined with passenger compartment discriminating sensor.

DISCRIMINATING SENSORS

Most SIR systems have 2 discriminating sensors. Some vehicles have 2 forward discriminating sensors, while other vehicles have one forward discriminating sensor and a passenger compartment discriminating sensor, or 2 mid-rail discriminating sensors. Forward discriminating sensor is located on radiator support brace or tie bar. Passenger compartment discriminating sensor is located under center of instrument panel/console area or under front passenger seat. Mid-rail discriminating sensors are located on side mid-rails in engine compartment.

In some vehicles, the passenger compartment discriminating sensor is combined with arming sensor. Discriminating sensors are wired in parallel on the ground side of deployment loop. These sensors are calibrated to close when deceleration velocity changes are severe enough to warrant deployment.

Sensors consist of a sensing element, normally open switch contacts, and a diagnostic resistor. Sensing element closes the normally open switch contacts when vehicle velocity changes are severe enough to warrant deployment.

A diagnostic resistor is connected in parallel with the normally open switch contacts within each of the sensors. These parallel resistors supply the ground path for current passing through the deployment loop during normal undeployed conditions. This small current flow results in a voltage drop across each component within loop. DERM monitors these voltage drops to detect circuit or component faults.

SIR COIL ASSEMBLY

SIR coil assembly consists of 2 current-carrying coils. It is installed in steering column and allows rotation of steering wheel while maintaining continuous (directly wired) contact of deployment loop through steering wheel inflator module. Slip rings are not used in SIR system to transmit current from column to steering wheel.

Gold-plated terminals and a shorting bar are used on coil assembly lower steering column Yellow connector. Shorting bar shorts the circuits to main coil and steering wheel inflator module when lower steering column connector is disconnected. This shorts the circuit to the inflator module(s), preventing unwanted deployment of the air bag(s) when servicing the steering column or other SIR components.

INFLATOR MODULE

When the vehicle is in an accident of sufficient force to simultaneously close the arming sensor and at least one discriminating sensor, nitrogen gas inflates the cloth bag packed inside the steering wheel hub and in passenger-side instrument panel, (if equipped). The bag(s) inflate in less than 1/20 of a second. As air bag is contacted by driver or passenger, the gas is vented through openings in the bag, which deflates almost as soon as it is completely deployed.

RESISTOR MODULE

Resistor module is located in SIR harness between inflator module and DERM. Resistor module allows DERM to monitor deployment loop for faults and to detect when a deployment has occurred.

Resistors in resistor module are balanced with resistors on arming and discriminating sensors to allow DERM to monitor voltage drops across the components of the deployment loop. Faults are detected during normal undeployed conditions by monitoring these voltages. On some vehicles, resistor module is mounted on DERM.

SYSTEM OPERATION CHECK

If system is functioning normally, air bag warning light flashes 7-9 times when ignition switch is turned to ON position and goes out.

Four possible warning light conditions can indicate a system failure

1. Light does not illuminate at all.
2. Light comes on while vehicle is driven.
3. Light flashes 7-9 times, and remains on.
4. Light does not flash but remains lit when ignition is turned on.

SIR system faults are usually due to a disconnected/loose electrical connector caused by previous service on vehicle. Always check Yellow SIR connector at base of steering column for loose or damaged wiring.

POST-COLLISION INSPECTION

When a vehicle has been involved in a collision, certain components of the passive restraint system must be inspected or replaced. See PASSIVE RESTRAINT SYSTEM INSPECTION article in the GENERAL INFORMATION section for post-collision inspection information.

INTERMITTENTS & POOR CONNECTIONS

Most intermittents are caused by faulty electrical connections or wiring, or a sticking relay or solenoid. Items to check are

1. Poor mating or connector halves, or terminals not fully seated in connector
2. Dirt or corrosion on terminals. Terminals must be clean and free of any foreign material which could impede proper terminal contact.
3. Damaged connector, exposing the terminals to dirt and moisture, as well as not maintaining proper terminal orientation with the component or mating connector.
4. Improperly formed or damaged terminals. All connector terminals in problem circuit(s) should be checked carefully to ensure good contact.
5. Connector Test Adapter Kit (J-35616-A) must be used whenever a diagnostic procedure requests checking or probing a terminal. Using adapter will ensure that no damage to terminals will occur, as well as giving an idea whether contact is sufficient.
6. Poor terminal-to-wire connections. some conditions which fall under this description are poor crimps, poor solder joints, crimping over wire insulation rather than the wire itself, or corrosion in the wire-to-terminal contact area.
7. Wire Insulation which is rubbed through, causing an intermittent short as the bare area touches other wiring or parts of vehicle.
8. Broken wires inside insulation. Perform continuity check while flexing wiring harness to find location of broken wires.

SERVICE PRECAUTIONS

SYSTEM REPAIR

Before any repairs are performed, disconnect and shield battery ground. Because system has ability to retain voltage, remove SIR or AIRBAG fuse, and disconnect Yellow SIR connector at base of steering column, and, on vehicles with passenger-side air bags, disconnect Yellow SIR connector at base of right instrument panel (behind knee bolster).

Wait 2 minutes before working on vehicle. All connectors used on SIR system use Connector Position Assurance (CPA) clips to ensure connector retention. Even if system is disconnected, always use caution when working near inflator modules.

SENSOR HANDLING

Use special care when handling a sensor. DO NOT strike or jar a sensor, as air bag deployment, personal injury or improper operation of SIR system could result. A sensor must be replaced if dropped 3 feet or more. Sensors and mounting bracket bolts must be carefully torqued to ensure correct operation. Never power up SIR system when any sensor is not rigidly attached to vehicle, since sensor is easily activated and could cause air bag deployment.

LIVE INFLATOR MODULE HANDLING

When carrying a live inflator module, ensure bag and trim cover are pointed away from body. If an accidental deployment occurs, bag will then deploy with reduced chance of injury. When placing a live inflator module on a bench or other surface, always face bag and trim cover up and away from surface so space is provided to allow air bag to expand in case of deployment. In addition, never carry any SIR component by wires or connector.

SPECIAL TOOLS

To avoid deployment when working on SIR system, DO NOT use electrical test equipment such as test lights, battery or A/C-powered volt/ohmmeter, or any type of electrical equipment other than those specified by manufacturer. See SIR RECOMMENDED TOOLS table.

SIR RECOMMENDED TOOLS

DISABLING & ACTIVATING AIR BAG SYSTEM

DISABLING SYSTEM

Note. With AIR BAG fuse removed and ignition switch ON the SIR warning lamp will be lit. This is normal operation and does not indicate a fault.

1. Turn steering wheel to place vehicle wheels in straight-ahead position. Turn ignition switch to LOCK position.
2. Remove SIR or AIR BAG fuse. Remove knee bolster. Remove CPA clip and disconnect Yellow SIR connector at base of steering column (it may be necessary to remove left sound insulator). If equipped with passenger-side air bag, disconnect Yellow SIR connector under right instrument panel or behind glove box door assembly. Some models have access to connector through a trap door in glove box.
3. Wait 2 minutes before beginning service. All connectors in SIR system use CPA clips to ensure connector retention. Even if system is disconnected, use caution when working near air bags.

ACTIVATING SYSTEM

Connect Yellow SIR connector at base of steering column, and under right side instrument panel, if equipped. Install CPA clips and fuse. Install knee bolster. Turn ignition switch to RUN position and ensure AIR BAG warning light flashes 7-9 times and then goes out.

Scheme 1

1. If coil assembly has been removed from steering column and is being reinstalled, go to next step. New coil assemblies are provided pre-centered and include a Blue plastic tab that is snapped off once coil is installed. (Scheme 1)
2. Ensure front wheels face straight ahead when installing or removing a coil assembly. If coil is removed without wheels in straight-ahead position and steering wheel has not been moved, same coil can be reinstalled if coil hub has not been rotated.
3. Hold coil assembly with clear bottom upward to see coil ribbon. Note there are 2 different styles of coil assemblies: one rotates clockwise and other counterclockwise.
4. While holding coil assembly housing, depress spring lock and rotate hub in direction of arrow until it stops. Coil assembly should now be wound up snug against center hub. Rotate coil assembly hub in opposite direction approximately 2 1/2 turns. Release spring lock between locking tabs in front of arrow.

DISPOSAL PROCEDURES

DEPLOYED AIR BAG

Once an inflator module has been deployed, surface of air bag may contain a small amount of sodium hydroxide dust, combined with a White packing powder. Sodium hydroxide dust can be irritating to skin if left on for an extended period of time. Always wear gloves and safety glasses when handling a deployed inflator module. Wash hands with mild soap and water afterward. Deployed air bag modules can be disposed of as would any other part. Handle air bag module with gloves, and wear safety glasses.

UNDEPLOYED AIR BAG

Undeployed air bag modules must not be disposed of at normal refuse locations. Undeployed air bag modules contain substances which can cause illness or injury if handled improperly. Disposal of air bag module in any manner inconsistent with proper procedures may be a violation of federal, state and/or local laws. If possible, deploy air bag module in vehicle. See SCRAPPED VEHICLE .

Transportation of undeployed inflator modules is regulated by hazardous materials regulations of U.S. Government Department of Transportation and most state governments. Special shipping procedures must be followed. Check with hazardous material section of state government for applicable shipping requirements.

SCRAPPED VEHICLE

Some vehicles which have to be scrapped may have undeployed SIR systems. When scrapping a vehicle with an undeployed module

1. Turn ignition switch to OFF position. Remove SIR fuse. Disconnect Yellow 2-pin connector at base of steering column. Cut harness side of SIR wiring approximately 3-6" from Yellow 2-pin connector.
2. Splice 2 wires at least 20 feet long to wiring cut from SIR harness. Connect Yellow 2-pin connector.
3. Ensure inflator module is secured to steering wheel. Remove all loose objects from front seat, and ensure no one is in vehicle. Stretch wires away from car as far as possible.
4. Connect wires to a 12-volt battery. Air bag should deploy. DO NOT touch inflator module area for 20 minutes due to heat generated during deployment. Wear gloves and safety glasses before handling deployed air bag. Wash hands with mild soap and water afterward.
5. On vehicles with passenger-side air bags, repeat deployment procedure for passenger-side. Access Yellow 2-pin connector at base of right instrument panel (behind knee bolster) or behind glove box door assembly.

REMOVAL & INSTALLATION

Removal

1. Before proceeding, follow air bag service precautions. See SERVICE PRECAUTIONS. Disable air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM.
2. DERM is located behind left-center of instrument panel. Remove DERM from mounting bracket and then remove CPA clip and disconnect electrical connector. (Scheme 2)

Scheme 2

Installation

To install, reverse removal procedure. Reactivate air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM . Check AIR BAG warning light to ensure system is functioning correctly. See SYSTEM OPERATION CHECK.

1. Before proceeding, follow air bag service precautions. See SERVICE PRECAUTIONS. Disable air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM.
2. Arming sensor is located next to center crossmember, under driver seat. Raise and support vehicle. Remove connector from retainer. Remove CPA clip. Unplug electrical connector. Unbolt sensor and remove. (Scheme 3)

Scheme 3

To install, reverse removal procedure. Torque sensor bolts to 10.7 Ft. Lbs. (14.5 N.m), after verifying arrow on sensor points toward front of vehicle. See DISABLING & ACTIVATING AIR BAG SYSTEM . Check AIR BAG warning light to ensure system is functioning correctly. See SYSTEM OPERATION CHECK .

1. Before proceeding, follow air bag service precautions. See SERVICE PRECAUTIONS. Disable air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM.
2. Forward discriminating sensors are located on forward sides of both frame rails. Lifting of vehicle may be necessary. If so, support securely after jacking. Remove bolts from sensor and unclip connector from retainer on frame. Remove CPA clip and unplug electrical connector. (Scheme 4)and (Scheme 5).

Scheme 4

Scheme 5

1. Align sensor to vehicle, ensuring arrow on sensor body is facing toward front of vehicle. Install fasteners, CPA clip and electrical connector and reinstall connector to retainer clip. Torque fasteners to 10.7 Ft. Lbs. (14.5 N.m).
2. Reactivate air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM. Check AIR BAG warning light to ensure system is functioning properly. See «SYSTEM OPERATION CHECK»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__system-operation-check) .

1. Before proceeding, follow air bag service precautions. See SERVICE PRECAUTIONS. Disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system) .
2. Remove inflator module. See INFLATOR MODULE under REMOVAL & INSTALLATION. Remove horn contact wire from steering column. Remove steering wheel hexagonal locking nut. Using appropriate puller, remove steering wheel. See STEERING WHEEL PULLER SPECIFICATIONS table.

STEERING WHEEL PULLER SPECIFICATIONS

Note. Front wheels of vehicle must be turned to straight-ahead position before beginning service. Failure to do so can result in coil assembly being removed without being centered. Reinstalling coil assembly under such circumstances causes ribbon in coil assembly to break when steering wheel is turned fully in one direction. Ensure key is always in LOCK position to prevent wheel from turning and uncentering coil assembly. To re-center coil assembly, see CENTERING COIL ASSEMBLY under ADJUSTMENTS.

1. Before proceeding, follow air bag service precautions. See SERVICE PRECAUTIONS. Disable air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM.
2. Remove inflator module. See «INFLATOR MODULE»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system) under REMOVAL & INSTALLATION. Remove horn contact wire from steering column. Remove steering wheel. See «STEERING WHEEL»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system) under REMOVAL & INSTALLATION. DO NOT install puller bolts too far, as damage to coil assembly can result.
3. Remove coil assembly retaining ring from steering shaft. Grasp clear plastic wire protector shield on underside of steering column, and slide downward. Partially remove coil assembly from end of steering wheel shaft and allow coil to hang freely. Note orientation to steering column housing before removal.
4. Remove wave washer from steering shaft. Using Lock Plate Compressor (J-23653-C), depress shaft lock and remove shaft lock retaining ring. Remove shaft lock plate and upper bearing spring. Remove turn signal canceling cam.
5. Remove hazard knob and attaching screw. Remove turn signal switch arm. Remove 3 turn signal switch screws and partially withdraw switch. Disconnect any remaining electrical connectors. Attach mechanics wire to coil assembly lower connector at base of steering column and carefully pull wire through gear shift lever bowl, column housing and lock housing cover.

1. Carefully feed coil assembly wire and lower connector through lock housing cover, column housing, and gear shift lever bowl. Allow coil assembly to hang freely. NOTE: Use care not to pinch wires when installing components. After wire is fed through, attach CAUTION tag to wire near connector at base of steering column. Tag is included in coil assembly repair kit.
2. Install turn signal switch and torque screws to 30 INCH Lbs. (3.4 N.m). Install turn signal switch arm and torque attaching screw to 20 INCH Lbs. (2.3 N.m).
3. Install hazard knob and attaching screw. Install turn signal canceling cam and shaft lock plate. Install shaft lock retaining ring. Using lock plate compressor, align block tooth on shaft, and depress shaft lock plate. Install wave washer.
4. Ensure coil assembly hub and steering shaft are centered. Coil assembly will become uncentered if column is separated from steering gear and is allowed to rotate, or if centering spring is depressed, allowing hub to rotate while coil assembly is removed from column.
5. Install coil assembly, using horn tower on canceling cam to align hole on inner ring of coil and projections on steering column housing with projections on outer ring of coil. To complete installation, reverse removal procedure.
6. Reactivate air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM. Check AIR BAG warning light to ensure system is functioning properly. See SYSTEM OPERATION CHECK.

Removal (Driver-Side) - Leaf Spring & Notched Pin-Type

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__service-precautions). Disable air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system). Disconnect negative battery cable.
2. Turn steering wheel 90 degrees to access rear shroud holes to inflator module. Using a screwdriver, push leaf spring to release pin. (Scheme 6) Turn steering wheel 180 degrees to access remaining shroud holes. Using a screwdriver, push leaf spring to release pin.
3. Tilt inflator module rearward from the top to access SIR wiring. Disconnect SIR lead wire from clip on inflator module. Disconnect SIR lead wire from clip on steering wheel. Remove Connector Position Assurance (CPA) clip and retainer from inflator module.

Scheme 6

Installation (Driver-Side) - Leaf Spring & Notched Pin-Type

1. Install Connector Position Assurance (CPA) clip and retainer to inflator module. Connect SIR lead wire to clip on steering wheel. Connect SIR lead wire to clip on inflator module. Install inflator module to steering wheel by firmly pressing module onto steering wheel and engaging notched pins in leaf spring. Ensure that wires are NOT pinched.
2. Install inflator module to steering wheel by firmly pressing module onto steering wheel enough to engage and latch all 4 notched pins in leaf spring. Ensure that wires are NOT pinched.
3. To complete installation, reverse removal procedure. Reactivate air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system) . Check AIR BAG warning light to ensure system is functioning properly. See «SYSTEM OPERATION CHECK»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__system-operation-check) .

Removal (Driver-Side) - Ball Lock Fastener-Type

1. Before proceeding, follow air bag service precautions. See «SERVICE PRECAUTIONS»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__service-precautions). Disable air bag system. See DISABLING & ACTIVATING AIR BAG SYSTEM. Disconnect negative battery cable.
2. Turn steering wheel 90 degrees to access rear shroud holes to inflator module. Using a ball-point pen or similar device, release 4 ball lock fasteners by pushing into the end of each fastener through holes in steering shroud. (Scheme 7)
3. Tilt inflator module rearward from the top to access SIR wiring. Disconnect SIR lead wire from clip on inflator module. Disconnect SIR lead wire from clip on steering wheel. Remove Connector Position Assurance (CPA) clip and retainer from inflator module.

Scheme 7

Installation (Driver-Side) - Ball Lock Fastener-Type

1. Install Connector Position Assurance (CPA) clip and retainer to inflator module. Connect SIR lead wire to clip on steering wheel. Connect SIR lead wire to clip on inflator module.
2. Install inflator module to steering wheel by firmly pressing module onto steering wheel enough to engage ball lock fasteners. Ensure that wires are NOT pinched.
3. To complete installation, reverse removal procedure. Reactivate air bag system. See «DISABLING & ACTIVATING AIR BAG SYSTEM»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__disabling-activating-air-bag-system) . Check AIR BAG warning light to ensure system is functioning properly. See «SYSTEM OPERATION CHECK»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system__system-operation-check) .

DIAGNOSIS & TESTING

Diagnostic Trouble Codes (DTCs)

Diagnostic Energy Reserve Module (DERM) provides a record of DTCs stored according to type. Current DTCs are faults presently being detected. Current DTCs are stored in Random Access Memory (RAM) and are erased when fault is corrected. Current DTCs can be read using a scan tester such as Tech 1, or on-board diagnostics on Cadillac vehicles.

Scan Tester Diagnostics

A scan tester will read and clear current codes and history codes. Ensure scan tester contains correct cartridge for SIR diagnostics. To use scan tester, connect it to DLC connector, plug in power source and turn ignition switch to ON position. Follow scan tester manufacturer instructions for communication with SIR system. Scan tester reads serial data from DERM data link output to DLC connector.

On-Board Diagnostics

On-board diagnostics can only be used on Cadillac models which have an on-board diagnostics panel. Enter diagnostics by depressing WARMER and OFF buttons on diagnostics panel. Service mode and codes will appear in display area. Current Code 51 (accident detected) cannot be cleared using on-board diagnostics; a scan tester is necessary to clear current Code 51. Current Code 34 will remain current after fault is repaired unless ignition is off long enough to allow 36-Volt Loop Reserve (36VLR) to fully discharge.

Note. Failure to follow diagnostic procedures may result in extended diagnostic time and incorrect diagnosis and parts replacement.

Diagnostic Procedure

1. «SIR DIAGNOSTIC SYSTEM CHECK»(/gmc/suburban/i-1992-1999/remont/airbag/#air-bag-restraint-system) should always be starting point of SIR diagnostics. See appropriate SIR DIAGNOSTIC SYSTEM CHECK under DIAGNOSTIC CHARTS. SIR DIAGNOSTIC SYSTEM CHECK checks for proper INFLATABLE RESTRAINT indicator light operation and SIR trouble codes using flash code and scan tester methods.
2. SIR DIAGNOSTIC SYSTEM CHECK will lead to correct diagnostic chart to diagnose SIR problems. Always perform SIR DIAGNOSTIC SYSTEM CHECK after repair or diagnostic procedures to ensure repair is correct and no other problems are present.

Description

Diagnostic procedures used in this section are designed to find and repair SIR problems. For best results, utilize diagnostic charts and follow sequence listed below

1. Perform SIR DIAGNOSTIC SYSTEM CHECK. SIR DIAGNOSTIC SYSTEM CHECK should be start of any SIR diagnosis. SIR DIAGNOSTIC SYSTEM CHECK checks for proper AIR BAG indicator operation and SIR trouble codes.
2. Refer to appropriate diagnostic chart as directed by SIR DIAGNOSTIC SYSTEM CHECK. SIR DIAGNOSTIC SYSTEM CHECK will lead to correct chart to diagnose any SIR problems. By-passing these procedures may result in extended diagnostic time.
3. Repeat SIR DIAGNOSTIC SYSTEM CHECK after any repair or diagnostic procedures are performed. Repeating SIR DIAGNOSTIC SYSTEM CHECK will ensure repair was made correctly and no other conditions exist. When ignition is first turned on, system voltage is applied from AIR BAG fuse to Diagnostic Energy Reserve Module (DERM) at IGNITION 1 input terminals A9 and A10, and from GAUGES fuse to DERM at REDUNDANT INDICATOR IGNITION 1 input terminal B2. DERM responds by flashing AIR BAG indicator 7-9 times. When engine is cranked, system voltage is applied to DERM at CRANK input. DERM grounds light circuit until system voltage is removed from CRANK input. This results in a steady AIR BAG indicator during cranking. After engine is cranked, DERM will again flash AIR BAG indicator 6 times.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. AIR BAG indicator should flash 7 times as ignition is just turned on.
2. As engine is cranked, AIR BAG indicator should remain on.
3. After cranking, AIR BAG indicator should flash 6 times and go off.
4. Checks for proper operation of SERIAL DATA circuit. This test also determines whether history DTCs are stored and, if they are, identify them.
5. Checks DERM's ability to communicate through SERIAL DATA LINE.
6. Test will refer to proper DTC chart to diagnose history DTCs stored in DERM memory.
7. Flashing of AIR BAG warning light 4 times during BULB CHECK indicates a malfunction in redundant lamp driver circuit. These malfunctions are diagnosed by DTC 62 chart.
8. Checks for proper operation of AIR BAG warning light and separates a "lamp on constantly" warning light fault from a "lamp never comes on" fault.
9. Checks for proper operation of SERIAL DATA circuit. Also identifies DTCs and determines if DTCs are current or history.
10. Requests technician to record all DTCs on repair order and refers technician to appropriate DTC chart.

Diagnostic Aids

Order in which DTCs are diagnosed is important. Failure to diagnose DTCs in order specified may result in extended diagnostic time, incorrect diagnosis, and incorrect parts replacement.

Scheme 8

When DERM recognizes IGNITION 1 voltage, applied to terminals A9 and A10, is in normal operating voltage range, AIR BAG warning light is flashed 7 times to verity operation. At this time, DERM performs TURN-ON tests followed by CONTINUOUS MONITORING tests. When no malfunctions are detected, DERM proceeds to INITIATOR ASSEMBLY RESISTANCE TEST. When a malfunction is detected, DERM sets a current diagnostic trouble code and illuminates AIR BAG warning light. DERM will clear current diagnostic trouble codes and move them to a history file when malfunction is no longer detected and/or ignition switch is cycled, except for DTC 51. DTC 51 can only be cleared using a scan tool CLEAR CODES command.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first if SIR system failure is suspected.
2. Confirms a current malfunction. If not-current malfunction is occurring, DIAGNOSTIC AIDS for appropriate DTC should be referenced. DERM should not be replaced for a history DTC.
3. Checks for malfunction introduced into SIR system during diagnostic process. It is unlikely a malfunctioning DERM would cause a new malfunction to occur during diagnostic process.
4. When circuit outside DERM has been found to operate properly, as indicated by appropriate diagnostic chart, then and only then should DERM be replaced.
5. DTC or symptom is no longer present. Malfunction may be intermittent, or may have been repaired during diagnosis of SIR system. Check system thoroughly for loose connections and other possible intermittent faults.

Scheme 9

When ignition is first turned on, IGNITION 1 voltage is applied from GAUGES fuse to REDUNDANT INDICATOR IGNITION 1, terminal B2, and to AIR BAG warning light which is connected to SIR INDICATOR, terminal B1. SIR fuse applies system voltage to IGNITION 1 inputs, terminals A9 and A10. DERM responds by flashing AIR BAG warning light 7 times. If IGNITION 1 is outside of normal operating voltage range, AIR BAG warning light will come on with no DTCs set. When engine is being cranked, IGNITION 1 voltage is applied from SIR CRANK SENSE fuse to DERM at CRANK input. DERM responds by grounding SIR INDICATOR output until IGNITION 1 voltage is removed from CRANK input. This results in AIR BAG warning light being on during cranking. After cranking, DERM will flash AIR BAG warning light 6 times.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS . Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 10

Scheme 11

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Open AIR BAG fuse will cause warning light to come on steady.
3. A disconnected DERM harness will cause warning light to come on steady via shorting bar from terminals A1 to B1.
4. Refer to note at top of Chart.
5. Refer to note at top of Chart. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
6. Checks for an open in IGNITION 1 circuit to DERM.
7. Checks for a short from SIR INDICATOR circuit to ground.
8. Checks for a short from CRANK input to voltage.
9. Checks if a short from CRANK input circuit to ground caused AIR BAG fuse to open. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
10. Checks if short to ground is due to malfunctioning arming sensor or short in wiring.

Scheme 12

When ignition is first turned on, system voltage is applied from GAUGES fuse to REDUNDANT INDICATOR IGNITION 1 terminal B2. SIR fuse applies system voltage to IGNITION 1 inputs, terminals A9 and A10. DERM responds by flashing AIR BAG warning light 7 times. When engine is being cranked, IGNITION 1 voltage is applied from SIR CRANK SENSE fuse to DERM at CRANK input. DERM responds by grounding SIR INDICATOR output until IGNITION 1 voltage is removed from CRANK input. This results in AIR BAG warning light being on during cranking. After cranking, DERM will flash AIR BAG warning light 6 times.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 13

Scheme 14

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether malfunction is in DERM or instrument cluster power feed circuit.
3. Refer to note at top of Chart.
4. Refer to note at top of Chart.
5. Refer to note at top of Chart. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
6. Refer to note at top of Chart.
7. Checks for an open in SIR INDICATOR circuit, instrument cluster circuit, and AIR BAG warning light bulb.
8. Checks whether malfunction is a short from SIR INDICATOR circuit to voltage.
9. Refer to note at top of Chart.
10. Refer to note at top of Chart.
11. Checks whether malfunction is a bad indicator bulb.
12. Checks whether malfunction is an open in SIR INDICATOR circuit or an open in instrument cluster. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
13. Checks for power in instrument cluster power feed circuit.
14. Checks for a short from instrument cluster power feed circuit to ground.
15. Checks if short to ground is fault in wiring harness or a malfunctioning DERM.
16. Refer to note at top of Chart.
17. Refer to note at top of Chart.
18. Checks whether malfunction is due to an open feed circuit from GAUGES fuse to instrument cluster, or an open power feed to GAUGES fuse.

Scheme 15

Scheme 16

When ignition is first turned on, system voltage is applied from GAUGES fuse to REDUNDANT INDICATOR IGNITION 1 terminal B2, and to AIR BAG warning light which is connected to SIR INDICATOR, terminal B1. SIR fuse applies system voltage to IGNITION 1 inputs, terminals A9 and A10. DERM responds by flashing AIR BAG warning light 7 times. When engine is being cranked, IGNITION 1 voltage is applied from SIR CRANK SENSE fuse to DERM at CRANK input. DERM responds by grounding SIR INDICATOR output until IGNITION 1 voltage is removed from CRANK input. This results in AIR BAG warning light being on during cranking. After cranking, DERM will flash AIR BAG warning light 6 times.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 17

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether malfunction is caused by an open CRANK fuse.
3. Refer to note at top of Chart.
4. Refer to note at top of Chart.
5. Refer to note at top of Chart. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions. NOTE: Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.
6. Checks for signal to CRANK input during cranking.
7. Checks whether lack of a proper crank signal is due to an open CRANK input circuit or an open power feed to CRANK fuse.
8. Checks whether CRANK fuse is open due to a short to ground in CRANK input circuit.
9. Checks whether short to ground is in wiring harness.

Scheme 18

When DERM recognizes IGNITION 1 voltage, applied to terminal A9 and A10, is in normal operating voltage range, AIR BAG warning light is flashed 7 times to verify operation. At this time DERM performs TURN-ON tests followed by CONTINUOUS MONITORING tests. When no malfunctions are detected, DERM proceeds to INITIATOR ASSEMBLY RESISTANCE TEST. When a malfunction is detected, DERM sets a current DTC and illuminates AIR BAG warning light. DERM will clear current DTCs and move them to a history file when malfunction is no longer detected and/or ignition switch is cycled, except for DTC 51. DTC 51 can only be cleared using a scan tool CLEAR CODES command.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 19

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Confirms proper operation of scan tool.
3. Incorrect connection to data link connector will prevent communications from being established.
4. Checks for general SERIAL DATA line malfunction. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions. NOTE: Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.
5. Refer to note at top of Chart.
6. Refer to note at top of Chart.
7. Refer to note at top of Chart.
8. Checks if malfunction is open in SERIAL DATA line or malfunction in DERM.
9. Checks for a short to ground in SERIAL DATA line.
10. Checks for a short to voltage in SERIAL DATA line.
11. Checks if malfunction is open in SERIAL DATA line or malfunction in DERM.

Scheme 20

Scheme 21

DERM monitors voltage at DRIVER SOURCE SENSE terminal A5, DRIVER-SIDE HIGH terminal B9, and DRIVER-SIDE LOW terminal B8 during CONTINUOUS MONITORING tests. When all voltages are simultaneously below a specified value for 500 milliseconds, DTC 14 sets.

Action Taken

DERM turns on AIR BAG warning light and sets DTC.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks for proper connection of arming sensor jumper harness electrical connector.
3. Checks for proper connection of arming sensor to SIR wiring harness.

It is unlikely an intermittent condition has set this DTC as this would require a poor connection at terminals "A" and "B", or at terminals "C" and "D".

Scheme 22

During initiator assembly resistance tests, DERM grounds DRIVER-SIDE LOW terminal B8, turns on driver current source at DRIVER-SIDE HIGH terminal B9, and injects a known amount of current into circuit.

Failure Conditions

Combined resistance of driver inflator module, SIR coil, harness wiring, circuits No. 347A and 348A, and connector terminal contact is greater than a specified value.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 23

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks for terminal deformation or contamination.
3. Checks whether malfunction is in driver inflator module circuit or in DERM wiring harness circuit.
4. Checks whether malfunction is in driver inflator module or in SIR coil assembly. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
5. Checks for high resistance in DRIVER-SIDE LOW circuit.
6. Checks for high resistance in DRIVER-SIDE HIGH circuit.

An intermittent condition is likely to be caused by a poor connection at Yellow 2-pin connector near base of steering column, DERM terminals B8 or B9, or connection at top of steering column to driver inflator module.

Scheme 24

During initiator assembly resistance tests, DERM grounds DRIVER-SIDE LOW terminal B8, turns on driver current source at DRIVER-SIDE HIGH terminal B9, and injects a known amount of current into circuit.

Combined resistance of driver inflator module, SIR coil, harness wiring, circuits No. 347A and 348A, and connector terminal contact is greater than a specified value.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether malfunction is in driver inflator module or in DERM or wiring harness.
3. Checks for short from DRIVER-SIDE HIGH to DRIVER-SIDE LOW circuit.
4. Checks whether malfunction is in driver inflator module or in SIR coil assembly.

An intermittent condition is likely to be caused by a short between circuit No. 347 and circuit No. 348, or a malfunctioning shorting clip at base of steering column. Test for diagnostic trouble code is only run while AIR BAG warning light is performing bulb check. When a scan tool CLEAR CODES command is issued and malfunction is still present, DTC will not reappear until next ignition cycle.

Scheme 25

During normal non-deployment operation of SIR system, small amount of current flows through driver deployment loop. Diagnostic resistors within arming sensor and discriminating sensors, along with resistance of inflator module, cause voltage drops within deployment loop.

Voltage at DRIVER-SIDE LOW terminal B8 is greater than a specified amount of DRIVER 36VLR for 500 milliseconds and DTC 35 is not set.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 26

Scheme 27

Scheme 28

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Determines whether malfunction is due to a component or wiring.
3. Checks for a short from DRIVER 36VLR circuit to DRIVER-SIDE LOW circuit.
4. Checks for a short from DRIVER 36VLR circuit to DRIVER-SIDE HIGH circuit.
5. Determines location of short from DRIVER 36VLR TO DRIVER-SIDE HIGH. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
6. Checks for an open between driver inflator module and discriminating sensor network.
7. Determines location of open in circuit No. 348.
8. Checks for an open in right forward discriminating sensor between terminal `"A"' and splice.
9. Checks for a short inside arming sensor. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
10. Checks for a short from DRIVER-SIDE HIGH circuit to DRIVER SOURCE SENSE circuit.
11. Determines location of short from DRIVER-SIDE HIGH circuit to DRIVER SOURCE SENSE circuit.
12. Checks for a partial short inside arming sensor.
13. Checks for increased resistance of left forward discriminating sensor and/or discriminating sensor jumper harness. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
14. Checks for increased resistance in left forward discriminating sensor.
15. Checks for increased resistance of right forward discriminating sensor and/or discriminating sensor jumper harness.
16. Checks for increased resistance in right forward discriminating sensor.

Intermittent condition is likely to be caused by backed out/shorted terminals on arming sensor harness connector or arming sensor jumper harness connector, poor connection at any of the discriminating sensor terminals, a short from circuit No. 236 to 347 or 348, a short from circuit No. 347 to 1400, or an open or high resistance in circuit No. 348B.

Scheme 29

Scheme 30

During normal non-deployment operation of SIR system, small amount of current flows through driver deployment loop. Diagnostic resistors within arming sensor and discriminating sensors, along with resistance of inflator module, cause voltage drops within deployment loop.

Voltage at DRIVER-SIDE LOW terminal B8 is less than a specified percentage of DRIVER 35VLR for 500 milliseconds during CONTINUOUS MONITORING.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 31

Scheme 32

Scheme 33

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether malfunction is occurring in steering column circuit.
3. Checks whether malfunction is due to a component or wiring. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
4. Checks for increased resistance in arming sensor.
5. Checks for partial short inside left forward discriminating sensor.
6. Checks for a partial short inside right forward discriminating sensor. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
7. Checks for an open in circuit No. 347.
8. Determines where open in circuit No. 347 is located.
9. Checks for a short from DRIVER-SIDE HIGH circuit to ground.
10. Checks for a short from DRIVER-SIDE LOW circuit to ground.
11. Checks for a short from discriminating sensor interconnect harness to ground. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
12. Checks for a short inside right forward discriminating sensor.
13. Checks for a short inside left forward discriminating sensor.

An intermittent condition is likely to be caused by a poor connection at DERM terminal A4 or arming sensor terminals "B" or "D", water intrusion in either discriminating sensor, an open in circuit No. 347B or a short to ground in circuits No. 347, 348 or 354.

If failure of discriminating sensor is suspected, perform following tests. Disconnect but do not unbolt discriminating sensor. Double check resistance values across terminals are within specification. Check resistance from each terminal to ground. Resistance should be greater than 2 megohms. If sensor fails either test, replace sensor.

See DTC 25 to diagnose a possible short to voltage. When malfunction occurs during ignition cycle, DTC 24 will set. If malfunction is still present at beginning of next ignition cycle, DTC 25 will set and DTC 24 will be moved to a history file.

Scheme 34

During INITIATOR ASSEMBLY RESISTANCE test, DERM grounds DRIVER-SIDE LOW terminal B8 and measures voltage at DRIVER-SIDE LOW. For a properly operating circuit, the voltage measurement during this test will be less than a specified value. When voltage measured at DRIVER-SIDE LOW is greater than a specified value, DTC 25 is set.

Voltage at DRIVER-SIDE LOW is above a specified value while DERM attempts to ground this terminal.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether fault is occurring in steering column circuit.
3. Checks for a short from DRIVER-SIDE HIGH circuit to voltage.
4. Checks for a short from DRIVER-SIDE LOW circuit to voltage.
5. Checks for a short from discriminating sensor interconnect to voltage.

This DTC can only be set when malfunction is present as ignition switch is turned on. After INITIATOR ASSEMBLY RESISTANCE TEST is completed, a short to voltage in steering column circuits No. 347, 348, or 354 will cause DTC 24 to set.

Scheme 35

When there is an open in driver inflator module or SIR coil assembly, resistance between DRIVER-SIDE HIGH terminal B9 and DRIVER-SIDE LOW terminal B8 increases. This causes a larger voltage drop from DRIVER-SIDE HIGH to DRIVER-SIDE LOW across a resistor inside DERM which connects these 2 terminals together. Increase in voltage difference between DRIVER-SIDE HIGH and DRIVER-SIDE LOW is detected by DERM during the CONTINUOUS MONITORING tests and DTC 26 is set.

Voltage difference between DRIVER-SIDE HIGH terminal B9 and DRIVER-SIDE LOW terminal B8 increases. This causes a larger voltage drop from DRIVER-SIDE HIGH to DRIVER-SIDE LOW across a resistor inside DERM which connects these 2 terminals together. The increase in voltage difference between DRIVER-SIDE HIGH and DRIVER-SIDE LOW is detected by DERM during CONTINUOUS MONITORING tests and DTC 26 is set.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether steering column malfunction is occurring.
3. Checks whether malfunction is in driver inflator module or SIR coil assembly.

DTC will only set when there is an improper connection of either Yellow 2-pin connector near base of steering column or Yellow 2-pin connector at top of steering column, an open SIR coil assembly, or an open inflator module.

Scheme 36

During INITIATOR ASSEMBLY RESISTANCE test, DERM grounds DRIVER-SIDE LOW terminal B8 and turns on DRIVER CURRENT SOURCE at DRIVER-SIDE HIGH terminal B9.

DRIVER-SIDE LOW voltage is less than a specified value while its initiator resistance is in range or when voltage measured at DRIVER-SIDE LOW is above a specified value.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

During INITIATOR ASSEMBLY RESISTANCE TEST, DERM checks for proper resistance of circuit No. 347A, 348A, SIR coil assembly and inflator module.

Scheme 37

During CONTINUOUS MONITORING tests, DERM monitors voltage at DRIVER SOURCE SENSE terminal A5.

Test Conditions

Voltage measured at DRIVER SOURCE SENSE terminal A5 is within a specified range or IGNITION 1 for 500 milliseconds during CONTINUOUS MONITORING.

Voltage at DRIVER SOURCE SENSE terminal A5 is within a specified range of IGNITION 1 for 500 milliseconds.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 38

Scheme 39

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
2. Checks for open in DRIVER 36VLR circuit between DERM and arming sensor jumper electrical connector.
3. Checks for open in DRIVER 36VLR circuit between arming sensor jumper harness connector and arming sensor.
4. Checks for high resistance but not an open in DRIVER SOURCE SENSE circuit between DERM and arming sensor electrical harness connector.
5. Checks for high resistance but not an open in DRIVER SOURCE SENSE circuit between DERM and arming sensor jumper harness electrical connector. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
6. Checks for a short from DRIVER SOURCE SENSE to voltage.

An intermittent condition is likely to be caused by a poor connection at arming sensor or arming sensor jumper harness terminal "B" or "C", poor connection at DERM terminal A4 or A5, an open in circuit No. 236 or 1400, or an open inside arming sensor.

Scheme 40

During TURN-ON tests performed at beginning of each ignition cycle, DERM delays charging of DRIVER 36VLR power supply. While delay is active, DERM measures voltage at DRIVER 36VLR terminal A4 and DRIVER SOURCE SENSE terminal A5.

Voltage at DRIVER SOURCE SENSE terminal A5 is a specified amount less than IGNITION 1 voltage and no higher priority faults are detected.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 41

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether a malfunction is occurring. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
3. Checks for an open in arming sensor ignition feed circuit.
4. Determines location of open in arming sensor ignition feed circuit.
5. Checks whether malfunction is an open in DRIVER SOURCE SENSE circuit or an open in arming sensor.
6. Determines location of open in DRIVER SOURCE SENSE circuit.

An intermittent condition is likely to be caused by an improper connection at arming sensor terminal "A" or "C", improper connection at DERM terminal A5, open ignition feed to arming sensor, open DRIVER SOURCE SENSE circuit, or malfunctioning arming sensor ignition diode. The test for this diagnostic trouble code is only run while AIR BAG warning light is performing bulb check. When a scan tool CLEAR CODES command is issued and malfunction is still present, DTC will not reappear until ignition switch is turned off for at least 2 minutes with entire SIR system connected, and then ignition switch is turned on.

Scheme 42

Scheme 43

During normal non-deployment operation of SIR system, a small amount of current flows through driver deployment loop. Diagnostic resistors within arming sensor and discriminating sensors, along with resistance of inflator module, cause voltage drops within deployment loop.

Voltage at DRIVER-SIDE LOW is within a specified percentage of its respective 36VLR power supply voltage for 500 milliseconds.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 44

Scheme 45

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks for increased resistance of left forward discriminating sensor.
3. Checks for an open in ground feed to left forward discriminating sensor. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
4. Determines location of open in ground feed to left forward discriminating sensor.
5. Checks for increased resistance of right forward discriminating sensor.
6. Checks for open in ground feed to right forward discriminating sensor. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
7. Determines location of open in ground feed to right forward discriminating sensor.
8. Checks for open in discriminating sensor interconnect circuit.
9. Checks for malfunctioning arming sensor.

An intermittent condition is likely to be caused by improper connection at any of the discriminating sensor terminals, an open in either discriminating sensor ground feed, or an open discriminating sensor interconnect circuit. Also, check for increased resistance in either discriminating sensor or decreased resistance of arming sensor.

Scheme 46

During TURN-ON tests performed at beginning of each ignition cycle, DERM delays charging of DRIVER 36VLR terminal A4 power supply. After delay has expired, DRIVER 36VLR power supply is allowed to charge.

Voltage at DRIVER 36VLR does not exceed a specified value within 10 seconds after IGNITION 1 voltage is first applied to DERM or, once having reached specified value, falls below specified value for 500 milliseconds during CONTINUOUS MONITORING.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether DERM has set DTC falsely.
3. Checks whether malfunctioning arming sensor is preventing DRIVER 36VLR from charging. This test will cause DTC 14 to set.
4. Checks whether short to voltage is preventing DRIVER 36VLR from charging.
5. Determines location of short to voltage which is preventing DRIVER 36VLR from charging.
6. Checks whether short to ground is preventing DRIVER 36VLR from charging.
7. Determines location of short to ground which is preventing DRIVER 36VLR from charging.

Scheme 47

Scheme 48

During normal non-deployment operation of SIR system, DERM monitors voltage supplied through arming sensor to high side of driver deployment loop at DRIVER SOURCE SENSE terminal A5.

Voltage at DRIVER-SIDE LOW terminal B8 is within a specified percentage of DRIVER 36VLR while simultaneously voltage measured at DRIVER SOURCE SENSE terminal A5 is a specified amount below DRIVER 36VLR for 500 milliseconds.

DERM turns on AIR BAG warning light and sets a Diagnostic Trouble Code (DTC).

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

Scheme 49

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks for an open in DRIVER SOURCE SENSE circuit. WARNING: To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Under no circumstances should battery powered test equipment or test light be used. Carefully follow all instructions.
3. Determines location of open in DRIVER SOURCE SENSE circuit.
4. Checks for a short from DRIVER SOURCE SENSE circuit to ground.
5. Determines location of short to ground in DRIVER SOURCE SENSE circuit.
6. Checks whether malfunction is caused by increased resistance across DRIVER SOURCE SENSE resistor in arming sensor.

An intermittent condition is likely to be caused by a poor connection to DERM at terminal A5, a poor connection to arming sensor or arming sensor jumper harness connector at terminal "C", an open or short to ground in circuit No. 1400, or a shorted arming sensor.

Scheme 50

Closure of arming sensor is detected when voltage measured at DRIVER-SIDE HIGH terminal B9 is within a specified amount of its deployment loop supply voltage. Closure of either discriminating sensor is detected when voltage measured at DRIVER-SIDE LOW terminal B8 is within a specified amount of ground potential. When both conditions are met simultaneously for not less tan 250 microseconds, CRASH DATA is recorded and DTC is set.

Diagnostic Trouble Code (DTC) sets when closure of arming sensor and at least one discriminating sensor is detected simultaneously for not less than 250 microseconds.

DERM turns on AIR BAG warning light and sets a DTC.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. When DTC 42 and DTC 51 are set simultaneously, perform DTC 42 diagnosis first.
3. If inflator module has not deployed, DTC 51 may have set falsely.
4. If DTC has set with no signs of frontal impact, DTC has set falsely.
5. When a frontal crash has occurred, it is necessary to perform indicated procedures to ensure SIR system is fully functional. See POST-COLLISION INSPECTION.
6. Checks for a DERM malfunction setting DTC.
7. Checks for a DERM malfunction setting DTC.
8. Determines whether DTC was set inadvertently during diagnosis or by DERM malfunction.

Scheme 51

If there is a frontal crash of sufficient force to activate arming sensor and at least one of 2 discriminating sensors simultaneously, DTC 51 is set, and DERM will record information regarding SIR system status and vehicle status in EEPROM.

DERM EEPROM area reserved for accident data is detected to be full.

DERM turns on AIR BAG indicator light and sets a DTC. DTC 52 must be cleared using scan tool CLEAR CODES command.

Scheme 52

During INITIATOR ASSEMBLY RESISTANCE tests, DERM grounds DRIVER-SIDE LOW terminal B8 and turns on driver current source at DRIVER-SIDE HIGH terminal B9.

Diagnostic Trouble Code (DTC) 53 sets when voltage difference between DRIVER-SIDE HIGH terminal B9 and DRIVER-SIDE LOW terminal B8 is greater than a specified value.

DERM turns on AIR BAG indicator light and sets a DTC.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether malfunction is caused by high resistance or open in DRIVER-SIDE LOW circuit.
3. Checks whether malfunction is due to high resistance or open in DRIVER-SIDE HIGH circuit.

An intermittent condition is likely to be caused by a poor connection at DERM terminal B8 or B9 or an open in circuit No. 347A or 348A. Test for this DTC is run only while AIR BAG warning light is performing bulb check. When a scan tool CLEAR CODES command is issued and malfunction is still present, DTC will not reappear until next ignition cycle.

Scheme 53

When IGNITION 1 voltage is first applied to DERM it will perform TURN-ON tests followed by CONTINUOUS MONITORING for one second. DERM also monitors DRIVER-SIDE LOW terminal B8 to ensure voltage is being applied to inflator module and monitors DRIVER SOURCE SENSE terminal A5 to ensure DRIVER 36VLR is supplying voltage to deployment loop. Ground is applied to terminal B7 (passenger-side low for a dual air bag DERM) and voltage is measured at DRIVER-SIDE LOW and terminal A6 (passenger source sense for dual air bag DERM). If grounding terminal B7 grounds DRIVER-SIDE LOW or voltage is measured at terminal A6, DTC 55 will set.

Diagnostic Trouble Code (DTC) 55 will set when no higher priority faults are detected during TURN-ON, no higher priority faults are detected during CONTINUOUS MONITORING for one second, no CRANK signal is present, and IGNITION 1 voltage is greater than a specified value. A dual air bag DERM has been installed in vehicle.

DERM turns on AIR BAG indicator light and sets DTC.

Scheme 54

When ignition switch is first turned on, battery voltage is applied to AIR BAG indicator light and to IGNITION 1 terminals A9 and A10. DERM responds by flashing AIR BAG indicator light 7 times alternating between primary and redundant lamp drivers.

Diagnostic Trouble Code (DTC) 61 will set when IGNITION 1 voltage is above a specified value and output state at SIR INDICATOR terminal B1 does not match commanded state of primary lamp driver for 400 milliseconds.

DERM attempts to turn on AIR BAG indicator light using redundant lamp driver and sets DTC.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. When DERM is configured for a serial data controlled warning light (smart cluster), DTC 61 will set. Clearing SIR diagnostic codes will reset DERM, allowing lamp driver in DERM to control AIR BAG warning light.

See CHART B and CHART C to diagnose warning light circuit malfunctions.

Scheme 55

When ignition switch is first turned on, battery voltage is applied to AIR BAG indicator light and to IGNITION 1 terminals A9 and A10. DERM responds by flashing AIR BAG indicator light 7 times alternating between primary and redundant lamp drivers.

Diagnostic Trouble Code (DTC) 62 will set when IGNITION 1 voltage is greater than a specified value and output state at SIR INDICATOR terminal B1 does not match commanded state of redundant lamp driver for 400 milliseconds.

DERM turns on AIR BAG indicator light using primary lamp driver and sets a DTC.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS. Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks for an open in REDUNDANT INDICATOR GROUND circuit.
3. Checks for an open in REDUNDANT INDICATOR IGNITION 1 circuit.

An intermittent condition is likely to be caused by a poor connection to DERM at terminal A2 or B2, an open in circuit No. 1590, or an open in circuit No. 39A.

Scheme 56

Diagnostic Trouble Code (DTC) 71 and/or 75 is an internal DERM fault. Codes set when DERM power supply reserve voltage charge or discharge time fails for 3 consecutive ignition cycles, DERM is unable to read from or write to EEPROM, DRIVER 36VLR is greater than a specified value for 500 milliseconds, or DERM calculated number for vehicle in which it is installed does not match value stored in EEPROM.

DERM turns on AIR BAG indicator light and sets DTC.

Scheme 57

During TURN-ON tests performed at beginning of each ignition cycle, DERM delays charging of DRIVER 36VLR power supply. While delay is active, DERM measures voltage at DRIVER 36VLR terminal A4 and DRIVER SOURCE SENSE terminal A5. When driver reserve diode is shorted, IGNITION 1 voltage is measured at DRIVER 36VLR from forward biased driver ignition diode. When voltage measured at DRIVER 36VLR is within a specified range of IGNITION 1 voltage for 8 consecutive TURN-ON tests, history Diagnostic Trouble Code (DTC) 83 is set.

DERM turns on AIR BAG indicator light and sets a DTC.

Note. Test numbers refer to test numbers on diagnostic chart. For circuit number identification, see WIRING DIAGRAMS . Breaks in numbering may occur throughout this test procedure. No steps have been omitted.

1. SIR DIAGNOSTIC SYSTEM CHECK should always be performed first.
2. Checks whether malfunction is caused by a shorted driver reserve diode within arming sensor.

DTC will not set as a current DTC. Follow chart to diagnose a history DTC 83.

Scheme 58

WIRE REPAIR

Because of sensitive nature of circuitry, manufacturer has developed special wiring repair procedures. Wire Repair Kit (J-38125-A) contains special sealed splices for use in repairing SIR wiring. Sealed splices are a heat shrink sleeve with sealing adhesive to produce a sealed splice and a cross-hatched core crimp to produce a positive contact for low energy circuits.

If any terminal or connector in SIR wire harness (except pigtails) is damaged, component can be repaired using one of connector repair assembly packs. Terminals in SIR system are manufactured from a special metal to provide necessary contact for low energy circuits. These terminals are only available in wiring kit, and no other terminal should be substituted.

If an SIR wire pigtail is damaged, entire component (including pigtail) should be replaced. Under no circumstances should wire, connector or terminal repair be attempted on arming sensor, passenger compartment discriminating sensor, forward discriminating sensor, inflator module, or SIR coil assembly.

If any wire except a pigtail is damaged, wire can be repaired by splicing in a new section of wire of same gauge. Sealed splices and crimping tool must be used for these splices. To open wiring harness, remove tape as necessary. To avoid wire insulation damage, manufacturer recommends use of a sewing seam ripper. Refer to instructions in kit for wire repair procedure.

CONNECTOR IDENTIFICATION

Note. To identify SIR wiring connector terminals (Scheme 59)-13.

Scheme 59

Scheme 60

Scheme 61

Scheme 62

Scheme 63

Scheme 64

Scheme 65

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

SIR System Wiring Diagram. Scheme 66

See also:
• PASSIVE RESTRAINT SYSTEM INSPECTION
• COMPUTER RELEARN PROCEDURES
• SIR RECOMMENDED TOOLS
• SCRAPPED VEHICLE
• SYSTEM OPERATION CHECK
• DISABLING & ACTIVATING AIR BAG SYSTEM
• SERVICE PRECAUTIONS