You don’t have to be ridingin a vehicle to be smackedin the face with an ex-ploding air bag. A bag candeploy in your service bayas you work on or near it,which is why it’s extremely important totake the proper precautions. If you do,you’ll be taking a big step toward avoid-ing being injured by a device designedto prevent serious injury.

Disconnecting the negative batterycable is the first essential step towardpreventing accidental deploymentwhen working on or near air bag sys-tems. In fact, it’s the primary precau-tion recommended to emergency ser-vice personnel attempting to removeinjured people from crashed cars withundeployed air bags. But that’s by nomeans all you need to know about pre-venting injury while working on oraround air bag systems.

Some air bags can deploy even if thebattery is disconnected. This reserveelectrical energy is built into some sys-tems to enable the air bags to deploy inthe event the battery is destroyed in afront-end collision. Generally, the re-serve energy lasts for about two min-utes. So if you were to disconnect thebattery and immediately go to work onor near an air bag component, youmight get more than you bargained for.You’d be wise to wait 10 minutes ormore before assuming an air bag sys-tem has been deactivated.

And aside from the safety considera-tions, deploying an otherwise good airbag can be a costly error. On some carsit might cost you, in addition to theprice of the air bag inflator module,the price of a windshield and cleanupof the associated mess involved whenair bags deploy.

SRS System ComponentsWorking effectively and safely on airbag systems requires a good knowl-edge of the various parts of such sys-tems, and how they work together.

Seat Belt Pretensioners. Essential-ly, a pretensionser uses a pyrotechnic gasgenerator to propel a piston attached tothe seat belt buckle with a cable. Whenthe air bag is deployed, the same circuit-ry fires this gas generator, which causesthe piston to pull on a cable, which

back-winds, or tightens, the seat belt.In addition to being aware of the

dangers of air bag deployment, you al-so need to be aware of accidentally de-ploying the seat belt pretensioners oncars so equipped. Seat belt pretension-ers should be stored in their originalcontainers on a secured flat surface.Keep them away from sparks, a heatsource or high electrical energy. Neverattempt to disassemble a pretensioner,and never reuse a deployed one.

Crash Sensors. When working onor near a crash sensor, be careful not tostrike or jar it. When installing thesesensors, make sure the brackets aren’tbent, which could lead to distortionwhen the mounting bolts are tighteneddown. Always check and torque crashsensors to specification.

Never power up an air bag system ifa crash sensor isn’t rigidly attached tothe vehicle; just pounding nearby

could trigger it to deploy the bag. Becareful when handling crash sensors;dropping one could damage it. Also, ifa sensor has damaged wiring or a dam-aged connector, don’t try to repair it.The repair could alter critical resis-tance specs and create problems foryou or the driver later on.

Make sure the crash sensor you’reusing to replace a damaged one is theright one for that car. “Looks the same”is not enough; you must be absolutelysure the replacement crash sensor isexactly the same as the damaged one.

Inflator Modules. Whenever youhandle an inflator module, keep inmind that you’re really dealing with aloaded gun. The module contains asmall cylinder which, when activated,triggers an immediate chemical reaction(usually with sodium azide or potassiumnitrate) to produce the nitrogen gasneeded to instantaneously inflate the air

24 March 1999

Whether you’re working on air bag systemsor just around them, following a few gener-al rules goes a long way toward preventinginjuries and incurring unnecessary costs.

BY BOB CERULLO

Living With

AIR BAGS

bag. When you carry an inflator mod-ule, never carry it by its wires; you coulddamage it. Make sure the bag openingpoints face away from you so that thesolid base will not propel toward you inthe event the bag accidentally deploys.

Always wear eye protection whenworking with or around air bag inflatormodules. Even if you aren’t injured bythe unexpected deploying bag poppinginto your face or hurling the metal baseat you, the corn starch or powder usedas a lubricant could irritate your eyes.

Similar precautions should be takenwith side-impact air bag modules, sincethey use essentially the same technolo-gy to inflate as do driver and passenger-side air bags. So before you startpounding or using a torch on a door,make certain you know whether or notthere’s a side air bag system lurking justbehind that area waiting to deploy.

Let’s say you’ve carefully removed a

steering column. You might be tempt-ed to stand it upside down on thesteering wheel away from the vehiclewhile you do other work. While that’s aperfectly safe procedure for steeringcolumns that do not contain an air bag,standing an air bag-equipped columnon the steering wheel is akin to havinga missile in your shop should the airbag accidentally deploy.

Never store an inflator module nearloose objects that could possibly slaminto it and trigger a deployment. Keepinflator modules away from flammableobjects that could, should a fire occur inyour shop, cause a module to deploy ifit ignites. Likewise, avoid storing infla-tor modules near a heat source thatcould produce temperatures higherthan 200°F. Most air bags are designedto deploy in a fire when temperaturesincrease near the steering column.

Let’s say you’re disposing of a

wrecked vehicle whose air bag neverwent off. Never ever discard an unde-ployed air bag module with shopgarbage. The safe thing to do is deploythe bag according to the car manufac-turer’s guidelines, then wait at least tenminutes after deployment before touch-ing or attempting to dispose of the infla-tor module. Remember, the metal sur-faces of a deployed air bag become veryhot and could burn you or cause a fire.Should a fire occur on a sealed inflator,most standard fire extinguishers can beused. If the unit is ruptured, use carbondioxide, dry chemical or foam. Finally,familiarize yourself with local, state andfederal laws regarding the proper dis-posal of deployed inflator modules.

DERMs, SISMs & SDMs. Whilethey don’t contain the rapid chemicalreaction cylinders found in inflatormodules, DERMs (Diagnostic EnergyReserve Modules), SISMs (Side Im-pact Sensing Modules) and SDMs(Sensing and Diagnostic Modules) alsorequire special handling. Essentially,what these and similar control modulesdo is provide diagnostic capability todetect when a system failure occurs. Inthe case of the SDM, both sensing anddiagnostic capabilities are offered.

Clocksprings. Clocksprings aresimilar in function to horn contacts inthe steering column in that they allowthe steering wheel to turn while main-taining electrical continuity betweenthe air bag module and the rest of thesystem. Despite its rugged-looking ex-terior, a clockspring is relatively easy todamage with improper handling. Somecarmakers require that it be replacedonce an air bag is deployed.

When replacing a clockspring, it’sessential to position the steering wheelso the front wheels are in the straight-ahead position. Also, keep the clock-spring in mind when removing thesteering column or replacing compo-nents such as a steering rack or gear.Once again, keep the steering wheellocked in the straight-ahead position toavoid accidental damage.

Fasteners. Exercise extreme cau-tion when removing rivets used to se-cure air bag modules and related com-ponents. Never drill them out. Sparkscreated when drilling could cause theair bag to deploy, or they could enter

Ph

otos

: Bob

Cer

ullo

25March 1999

the inflator module and cause injury topassengers should the bag deploy.

The important thing to rememberwhen working on any air bag-equippedvehicle is where you can expect to findthe various components and how totreat them. Make sure the mountingsurfaces of all components are cleanand free of grease or dirt. When acomponent has an arrow imprinted onit, make a note of which way the arrowis pointing. (Generally, it points towardthe front of the vehicle.) Check themanufacturer’s literature to ascertainexactly how the part is to be installed.

Always use a torque wrench to tight-en all fasteners. Don’t open any air bagcomponent package until you’re readyto do the installation. Before removinga DERM or other module from itspackaging, ground the unit to a known-good ground on the vehicle. This willeliminate any static electricity thatcould damage the module. Even whenhandling or removing these units froma vehicle, it’s a good idea to touch agood ground to remove any staticcharge that may have built up in yourbody. Just sliding across the seat,walking or getting up could create

enough of a charge to set off the air bag.Finally, make sure the adhesive you

use when installing a new windshield isthe type specified by the manufacturerthat will safely hold the windshield inplace when an air bag deploys. An im-properly glued windshield could popout and render the bag ineffective inan accident.

Your Test EquipmentArsenalMake sure you’ve got the proper testgear before you begin checking air bagwiring or probing other circuits thatmay have wiring running through oralongside air bag system wiring. You canaccidentally deploy an air bag if youhappen to hit the wrong wire with a bat-tery-powered test light, an analog volt-meter or ohmmeter, or any other typeof test equipment besides that specifiedas safe for use with air bag systems. Bythe way, don’t assume that just becauseyour test light is unpowered that it’s safeto use with an air bag system.

Scan tools can be very useful in di-agnosing air bag problems. Check withyour scan tool supplier to determine ifand how yours can be used. With somescan tools, you may need to purchaseadditional modules to be able to ex-tract air bag fault codes and data.

When you’ve completed a repair toany air bag system, keep in mind thatsomething could still not be quiteright. So when you turn on the ignitionkey to power up the system for the firsttime, stay out of the way of both thedriver-side and passenger-side bags.Remember, it’s entirely possible for airbags to deploy due to a malfunction,installation error or improperly donerepair, and if you aren’t in the way, youcan’t get pounded by a deploying airbag or sprayed with white powder.

Opinions vary on whether the whitestuff from deployed air bags is harm-ful. As well as the corn starch used tolubricate the bags, there may be asmall amount of sodium hydroxide re-leased, which quickly converts to sodi-um carbonate. These chemicals maycause some irritation, especially ifrubbed into the eyes—another reasonwhy eye protection should be wornalong with rubber gloves whenever

26 March 1999

LIVING WITH AIR BAGS

When an air bag deploys, it creates lots of dust in the passenger compart-ment that can irritate the eyes. A good pair of goggles is essential equipmentwhen working around deployed bags. Before releasing the car to the cus-tomer, always vacuum out the interior, including the heater and a/c ducts.

Air bags deploy with a tremendous amount of force, so be extremely carefulwhen working around any system component. An inadvertent deployment willcost you not only an inflator module but quite possibly a windshield, as well.

you’re handling deployed air bags. Be-fore delivering the car back to the cus-tomer, it would also be wise to vacuumthe interior and clean out any powderthat may have made its way into theheater/air conditioner ducts.

What Else Besidesthe Air Bag?You might assume that when an air bagis deployed, you need only replace theinflator module and maybe a sensor ortwo to get the car back in service. Factis, though, different carmakers makedifferent recommendations. For exam-ple, when an air bag deploys on a 1998Audi A4, in addition to the air bag mod-ule, Audi requires replacement of thecontrol unit and clockspring. For the1998 Acura TL, Acura calls for replace-ment of the diagnostic module and theseat belts in use at the time of the acci-dent. On 1998 BMW M3, 318, 323 and328 models, BMW wants the clock-spring, control module, crash sensors,safing sensor and seat belts replaced.

While these additional items may notseem altogether necessary, and youmight have difficulty convincing someunenlightened insurance adjustor or carowner that they are required, the factthat the carmaker says they’re mandato-ry should be sufficient justification. Plus,ignoring those recommendations couldopen up a whole can of legal worms ifan air bag fails to deploy when it should

after you’ve worked on the system.While all air bags perform essentially

the same function—protecting the driv-er or passenger in a collision—not allwork exactly the same way regardingtriggering and operation. Some Jaguarsand Jeeps, for instance, use mechanicalair bag systems, which are differentfrom the various electrically operatedsystems used by other carmakers.

One sure way to know what the car-maker requires—while at the sametime getting a good idea of how to re-pair each system and how long eachprocedure should take to perform—is

to consult a good manual, such asMOTOR’s Air Bag Manual. It shouldcontain all you need to know about airbags, including diagnosis, safety precau-tions, circuit diagrams, step-by-step re-pairs, flat rate times, component loca-tion and much more. If you do any airbag work, a good manual is a must.

27March 1999

Never discard an undeployed air bag with the normal shop trash. Deploy thebag following the car manufacturer’s specific guidelines, then properly dis-card the inflator module according to state or local regulations.

When installing a new inflator module into a vehicle, you don’t want to be di-rectly in front of the air bag, in case it accidentally goes off. Reaching in fromoutside the vehicle is definitely a much sounder, safer approach.

The inflator module contains the ex-plosive charge that allows the air bagto do its thing. When carrying a newmodule around the shop, make surethe opening points, or cutouts, in thematerial face away from you, just incase of an accidental deployment.

For a free copy of this article, write to: Fulfillment Dept.,

MOTOR Magazine, 5600 CrooksRd., Troy, MI 48098. Additional

copies are $2 each. Send check or money order.