Tires have been subject toflats, punctures andblowouts since the ad-vent of the first pneu-matic tires in the late1880s. Bicyclists and, lat-

er, motorists learned to check tire con-dition and inflation often by squeezingthe tire or eyeballing its profile. Actualpressure gauges were originally so ex-pensive that only professionals could af-ford them. Mass production of laterstick-type gauges rendered them cheapenough that today almost every car hasone—sitting unused—in the glovebox!

The debut of the 1986 Porsche 959heralded the first reported passengercar tire pressure monitoring system(TPMS). It incorporated a hollow tubewithin one spoke of the rim. Otherhigh-end European luxury cars followedsuit, and by 1990, the Renault Lagunahad become the first high-volume mid-size passenger vehicle sporting TPMSas standard equipment.

Fast forward. Beginning with the2008 model year, cars and light truckscarry a mandatory tire pressure moni-toring system, usually consisting of di-rect-reading pressure sensors installedin each road wheel. Some also carrysensors in their spare tires, althoughthese are not specifically required bylaw in the case of temporary (compact)spare tires. By 2014, the share ofTPMS-equipped vehicles on the road isexpected to reach 38%.

As a recent National Highway TrafficSafety Administration (NHTSA) reportnotes, “Proper tire inflation is importantfor several reasons. Underinflated tiresexperience a greater amount of sidewallflexion than properly inflated tires, re-sulting in decreased fuel economy, slug-gish handling, longer stopping dis-tances, increased stress to tire compo-nents and heat buildup that can lead tocatastrophic failure of the tire, such ascracking, component separation orblowout. These catastrophic failures cancause loss of vehicle control and may re-sult in a crash. Overinflated tires may bemore easily damaged by potholes or de-bris. Severe overinflation may increasestopping distance due to reduced areaof road contact and nonoptimal traction,and may also contribute to vehicle insta-bility. As with underinflation, overinfla-

tion may result in uneven tread wearthat reduces the useful life of the tire.”

As you might expect, safety—theirmiddle name!—is of paramount concernto the NHTSA folks. That’s a blessing,because if it were only about the fuelsaved, the same report concludes thatthe average driver of a TPMS-equippedcar would save a whopping 9.32 gallonsof gas in the first eight years of operation.The numbers are slightly more com-pelling for light trucks: 27.89 gallons overthe same eight-year period. Either way,

it’s hard to justify the cost in terms of fuelsavings alone, so you have to factor inboth decreased tire wear and the puta-tive safety benefits to come even close toan economic break-even for TPMS.

Five years ago, accidental breakageaccounted for the vast majority ofTPMS sensor replacements. But now,many of the first-generation sensor bat-teries have begun to fail, accounting forthe majority of current sensor replace-ments. Most sensor batteries cannot besuccessfully replaced independently of

20 June 2013

the sensor, as the batteries are typicallyencased in a moistureproof potting ma-terial. (While it would be theoreticallypossible to melt out the potting materi-al, solder in a new battery and repot thesensor, it would be economically pro-hibitive vs. simple unit replacement.)

With a projected battery life span ofsix to ten years, expect to see an ever-in-creasing number of such failures incoming years as the pool of aging sen-sors increases. To put that concept intoperspective, consider this: Total U.S. car

sales during 2012 totaled around 14.5million units. Projecting future replace-ment needs some six to ten years out,and allowing for some attrition due toaccidents and other factors, last year’svehicles alone will eventually result inthe need for some 50 million TPMSsensor replacements.

What’s your share? There are rough-ly 175,000 automobile service facilitiesin the U.S., some 10% of which arenew-car dealership service depart-ments. If the work were all done and

spread out evenly, every shop in thecountry would expect eventually to re-place around 300 sensors per year. Withwholesale prices ranging from a low ofaround $25 to a high somewhere northof $80 per sensor, this represents a sig-nificant market. A quick survey of retailprices in my local area netted quotesfrom $20 to $50 per tire for labor on topof parts. This included mounting, bal-ancing and any necessary reprogram-ming or relearning services.

Of course, under current law in mostjurisdictions, consumers are not re-quired to repair or replace TPMS sen-sors or systems in the event of failure, sosome percentage of those anticipatedreplacements may never occur (but, see“Legal Issues” on page 26 for an impor-tant caveat). If you think those numbersmake a compelling case for getting seri-ous about TPMS work, consider this:We’re fast approaching a population of100 million TPMS-equipped vehicles.That means that somewhere around aquarter to a third of all vehicles servicedare currently equipped with TPMS.The numbers and percentages will risefrom here.

If one sensor battery quits, are theothers far behind? Given the tight uni-formity of modern manufacturing, oddsare that a battery failure in one sensor islikely to be followed by three more infairly rapid succession. At the very least,group replacement becomes a prudentsuggestion if the tires are nearing theend of their useful life as well.

Some sensors will report current volt-age and/or remaining battery life per-centage in datastream. This information,along with information as to drivinghabits, can allow you to tailor your ser-vice suggestions appropriately. In gener-al, most vehicle manufacturers’ monitor-ing algorithms consume less batterypower per mile or per unit time underhighway driving conditions than duringstop & go driving. A remaining batterylife of, say, 10% might be enough fortwo years of mostly highway driving, butperhaps only a half or even a quarter ofthat time in city driving conditions.

State of the ArtDirect-reading sensor systems (dTPMS)are those that rely on integral batteries,sensors, transmitters and associated cir-

21June 2013

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TPMS SENSORS REACH

RETIREMENT AGE

TPMS SENSORS REACH

RETIREMENT AGEBY SAM BELL

Many first-generationTPMS sensors are begin-ning to ‘retire,’ or simplydie of old age. This shouldlead to an uptick in con-sumer awareness ofthese systems, and anincrease in related servicework for your shop.

cuitry. While the role of the main com-ponents is clear, the “associated circuit-ry” may hold a few surprises. Most suchTPMS sensors incorporate circuitryspecifically designed to preserve and ex-tend battery life. Using motion-sensingcircuitry allows the pressure sensingand transmitting circuits to be switchedoff when the vehicle is stationary. Addi-tionally, since federal regulations re-quire that the system update at leastevery 20 minutes, each wheel sensor ispotentially allowed to sleep for up to 19minutes at a time, if the manufacturerso chooses. In practice, few manufactur-ers stretch the reporting interval thatfar, but it’s not surprising to see updaterates of three to ten minutes.

The earliest indirect-reading TPMSsystems (iTPMS) relied on ABS wheel-speed sensors to detect any wheel con-sistently spinning faster than the others.Since an underinflated tire has a slightlyshorter running circumference, it has togo more revolutions to cover the sameroad distance. However, these early sys-tems were not good at noticing when allthe tires were equally low, as typicallyhappens when colder weather sets in(see “Shrinkage! The Combined GasLaw of the Temperature/Pressure Rela-tionship” above). This shortcoming ledmost vehicle manufacturers to abandonthis technology in favor of the more ex-pensive direct-reading type.

Further research has revealed, how-ever, that certain wheel-speed signalcharacteristics are highly sensitive to

tire pressure. This allows some newerindirect-reading systems to incorporatethe ability to analyze certain frequen-cies, spectra and other features of thewheel speed sensor’s signals with suffi-cient certainty to detect reduced infla-tion in as many as all four tires. In suchcases, the TPMS function is handled bythe ABS/VSC control module.

Most such second-generation iTPMSapplications rely on a push-button ormenu-selected manual reset procedureto reinitialize system response to varia-tions due to tire brand/replacement,construction and wear, as well as individ-

ual driving styles and speeds. The resetprocedure may require data acquisitionover time periods as long as an hour be-fore the system has fully learned the sig-nal characteristics. In many cases, even asimple tire rotation will require a reset,as the signal characteristics for a giventire and wheel may vary, depending onmounted position.

Direct-reading sensors incorporatebatteries and other toxic materialswhich should not be disposed of in thenormal waste stream. Incineration re-leases toxic fumes, while heavy metalsand rare-earth minerals will eventually

TPMS SENSORS REACH RETIREMENT AGE

22 June 2013

Shrinkage is a cold-temperature factof life. For a given amount of a gas(like air in a balloon), the pressure

increases proportionately with the tem-perature and decreases proportionatelywith the volume. This means that if youheat or squeeze a balloon, its internalpressure will increase. If you cool it, thepressure drops and the balloon shrinksalong with it.

Why does it matter? You’re just get-ting to a car that’s been sitting in yourlot for several hours on a sunny autumnafternoon. It’s 68° outside and your in-frared temp gun confirms that the tiresare at that temperature as well. Tonightis forecast to be the start of a cold snap.The cold-tire inflation specification callsfor 32 psi. Part of your job on this car isto winterize it. What inflation pressureshould you select? If you set the tires to

32 psi now, they’ll be down to 29 psi to-morrow morning, and will just get low-er as the weather continues to cool. Abetter choice might be to bump themup to around 36 psi, which should keepthem within 1 psi of their cold target in-flation throughout the coming monthsfor temperatures as low as 16° and ashigh as 44°.

You may also need to calculate an ap-propriate hot-tire inflation pressure ifyou need to adjust a tire after the vehi-cle has been driven. Use your infraredtemp gun to determine the current tiretemperature, then be sure to factor intomorrow’s anticipated cold morningtemperature. Truly hot tires may need tobe set 4 or more psi above the cold specin order to come out right. Getting themath right helps ensure your customer’ssafety.

Shrinkage! The Combined Gas Law of theTemperature/Pressure Relationship

This TPMS icon lights up on a lot of dash-boards. Nine times out of ten, the imme-diate solution is simply to check and ad-just the tire pressures. And, of course,you already know that if the weatherhasn’t recently taken a turn for the cold-er, you should check for a leak that mighthave caused the affected tire to lose air.

The vast majority of direct-readingTPMS sensors are integrated withthe valve stem. When dismounting

a tire equipped with such a sensor, youshould always remove the cap and re-taining nut and allow the sensor to“drop” inward in order to avoid break-ing the sensor. Be sure to replace thevalve stem nut, rubber grommet andnickel-plated valve core itself everytime you move or reinstall the sensor.With some Siemens-type sensors, youmay also have to replace the metal ringat the base of the valve stem. Alwaysuse plastic or rubber caps only, as metalones can quickly corrode and bondwith the aluminum valve stem. Thephoto on page 26 shows the result of a

metal cap having been used during asalty winter’s driving season. Missingcaps should always be replaced, as ex-cessive dirt or moisture can ruin a goodsensor.

A properly calibrated and maintainedtorque wrench is needed to ensureproper sealing with no damage to ex-pensive components. Corroded nuts andpreviously compressed grommets maynot seal correctly, and overtightening inan effort to make them do so could leadto sensor damage. The new grommetand nut allow you to be reasonably con-fident that the specified torque willachieve the desired seal, provided thatyou properly cleaned the sensor mount-ing area.

Care & Feeding

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leach out under landfill conditions, po-tentially contaminating both soils andgroundwaters. Some municipal, county,regional or state agencies accept TPMSsensors for dismantling, recycling andappropriate disposal under the sameprograms governing general electronicwaste, so you should check those op-tions first.

If no other option is available, it’s easyenough to break most sensors apart toremove at least the spent batteries whichcan then be recycled along with all the

other button-cell units you replace incustomer key fobs. Remaining electroniccomponents can be recycled with otherpost-consumer electronic waste materi-als. Customers respond very positively tosuch efforts, so be sure to let them knowthe part you play in the industry that’sthe world’s largest recycler.

State of the LawRecently, the Tire Industry Association(TIA) asked NHTSA for clarificationon several TPMS scenarios. Try your

hand at answering each of these beforereading on:

Already broken. Your customercomplains of a flashing TPMS light, andyou determine that one of the sensors,incorporated into a valve stem, is faulty.The customer declines to replace thefaulty sensor. Is it legal for you to replacethe faulty sensor with a conventionalsnap-in rubber valve stem? Does youranswer change if the sensor in questionalso leaks?

Winter wheels. Your customer pur-

TPMS SENSORS REACH RETIREMENT AGE

The sensor portion is really no different from a MAP sensorcircuit in that it needs power, ground and signal. Some in-corporate temperature sensing as well. The rest of the cir-cuitry simply conserves battery life and power whilebroadcasting the data to a receiver mounted in the vehicle.

24 June 2013

Most direct-reading TPMS sensors rely on a nonreplace-able battery that’s integrally molded into the sensor as-sembly. Many are lithium-based, and many of the oldestones are now reaching the limits of their longevity.

Iwish I could report that there is a singleuniversal system or procedure for reset-ting or retraining TPMS sensors or sys-

tems. Some are quite straightforward: Af-ter setting the inflation of each tire tospec, you push a reset button on the dashor console for a few seconds, the lightgoes out and you’re done. Some, unfortu-nately, require a more complex set of pro-cedures, which can include driving at sev-eral specific speed ranges for specified pe-riods of time. According to Tire Rack, forexample, one Buick Rendezvous requiresdriving in a straight line at specifiedspeeds including 75 mph or above for 10to 20 minutes, all after a lengthy series ofignition key manipulations and buttonpushes!

Of course, professional-level tools canusually cut right to the chase, giving youthe data and resources you need to accu-rately and efficiently diagnose, initializeor retrain sensors safely and profitably.Refer to an authoritative source, such asMOTOR’s Tire Pressure Monitoring Guideor MOTORALLDATA for complete proce-dures and specifications. Bartec, an indus-try leader in TPMS tools, equipment, parts

and supplies, hosts a specialized websiteat www.tpmshub.com that features solidinformation, including tips on some of themore troublesome vehicles and systems.

Reset. Vehicles that report individualinflations for each wheel may need tohave a reset after a tire rotation so thateach wheel can be reported in its new lo-cation. If this info is available on thedashboard or control console, you canquickly check whether a reset is necessaryby letting a few pounds of pressure outfrom one tire while monitoring its dis-play. If the display shows the drop at thecorrect corner, the system probably needsno further reset beyond correcting theinflation you just changed. If the drop isreported as being on another corner, youmay have to reset the system to reflectthe current positioning.

Retrain. Some vehicles will automati-cally acquire and register new TPMS sen-sor identities after replacement when driv -en. Many others will not. New sensorsmay require “registration” via a special-ized TPMS tool, or even via a dealership-level scan tool. In most cases, you can usu-ally “clone” the original sensor with a spe-

cialized cloning tool that writes the origi-nal sensor’s identity to the new compo-nent. Often this will be faster and easierthan any other method, but it may still re-quire clearing any previously set DTCs andperforming any other necessary relearnsteps. (A recent offer from one of my sup-pliers featured an assortment of 12 popu-lar cloneable sensors and a basic cloningtool for $399, so this option may not beout of reach for the average shop.)

Why does this matter? Performing theTPMS relearn procedure after every TPMSservice provides your shop with a set ofbaseline data so you can quickly verifythat any DTCs are based on recent events,not leftovers from the past. This will alsoact as a quality control check and allowyou to catch any problems before theyleave the shop. A consistently executedshop policy in this regard will also helpshield you from future liability and fromcustomer misunderstandings. Like anyvalue-added service, you should chargefor it or, at the very least, highlight it asevidence of an extra level of attention todetail that differentiates your shop fromthe competition.

Resetting & Retraining

chases a set of winter tires and rims forinstallation on his TPMS-equipped vehi-cle. The winter wheels are not equippedwith TPMS sensors. Is it legal for you toinstall them? Does your answer changeif his TPMS light is already flashing withhis regular tires on?

Oops. In the course of other work,you inadvertently damage a previouslyworking TPMS sensor, rendering it in-operative. You cannot procure anothersensor before the close of business. Is itpermissible to put in a standard valvestem and allow the customer to take hisvehicle? Does your answer change if youmake an appointment with the cus-tomer to return for the new sensor onanother day?

Dang. After performing some servicework, you return a car to your customerwith the TPMS light off, but it comes onafter being driven for 15 or 20 minutes.Are you guilty of violating NHTSA regu-lations? Does your answer change if anilluminated TPMS light was the cus-tomer’s original complaint? How about ifthe light was not illuminated previously?

The regulations which require TPMSalso prohibit knowingly making such asystem inoperative. A recent letter fromO. Kevin Vincent, Chief Counsel forNHTSA, addressed each of the scenar-ios above as posed by the TIA. Some ofthe answers may surprise you.

Already broken. Since the sensor isalready inoperative, you may replace itwith a standard valve stem. It doesn’tmatter if the original sensor is leaking or

not. Either way, you will not knowinglybe making the system inoperative; it al-ready is inoperative.

Winter wheels. NHTSA says youmust decline to install the wheels. Itspecifically rejects the argument thatsince the TPMS light would thenceforth

Irecently worked on a car where the cus-tomer’s chief complaint was that theleft front tire consistently reported a

low pressure in spite of being manuallyadjusted to spec. I guess it never occurredto him even to look at, much less tocheck, the rest of the tires, or he wouldhave found the nearly flat left rear.

While that may sound pretty silly, andperhaps says more about this customer’slimitations than he might like, it illus-trates the surprisingly high level of trustmost consumers place in the technologyof their automobiles. It also raises thequestion of how a jury might react in theevent of an accident caused by theblowout of a seriously underinflated butmisidentified tire. Would the technicianwho failed to retrain the tire locations af-ter a routine rotation be found liable?

From the consumer’s point of view,suppose a customer’s vehicle has devel-oped a TPMS problem of some sort thatresults in the TPMS light staying on eventhough the tire inflations are all correct.The situation has persisted for months,perhaps years, and the customer has de-cided to simply ignore the light. Then one

day he suffers a blowout brought on byprolonged driving on a severely underin-flated tire. He loses control of the car, andthe resulting crash leaves the occupantsof another vehicle badly injured.

Is this just a simple case of negligence?Or has the customer’s decision to ignorethe light raised his level of culpability towillful recklessness? And what differencedoes it make?

We’ll start with the criminal side first.While there may be a citation and a mis-demeanor offense conviction in conjunc-tion with a simple traffic accident, thecriminal consequences are usually prettyminor—typically, points on the driver’s li-cense and a fine. Reckless operation, onthe other hand, may result in greaterpenalties, possibly including jail time. Isthe driver’s decision to ignore the TPMSwarning light “reckless”? That’s a ques-tion a jury may someday have to decide.

On the civil side (money damages), inmost jurisdictions, a finding of simple negli-gence will result in an award of damages inan amount designed to put the injured par-ties back on their feet. Such a verdict, whichwould be paid under the driver’s liability in-

surance coverage, may include money forlost wages, medical bills, property damage,pain and suffering. In most states, however,if a jury finds the driver to have been will-fully reckless, the jury may also award addi-tional punitive damages designed to makea public example of the driver’s type of be-havior. Punitive damages are not coveredby any type of insurance. Furthermore,while compensatory damage judgmentsabove the limits of an insurance policy cansometimes be erased by bankruptcy, awardsfor punitive damages generally cannot be.

While I do not know of any such TPMS-based case at the moment, it’s not toofar-fetched to imagine that one will arise,probably sooner rather than later. (A simi-lar case involving continued operation inspite of an illuminated red brake warninglamp, for example, has already occurred.The outcome was a harshly punitive judg-ment against the willfully reckless driver.)

Bottom line: As Scott Holloway, CEOand general manager of Bartec, advises,to avoid a lawsuit, always test before youtouch, service the sensor wear items anddo the TPMS relearn every time! Soundslike good advice.

Legal Issues

TPMS SENSORS REACH RETIREMENT AGE

26 June 2013

Tire pressure specs are always for a coldtire. But you don’t always get to workon cold tires, especially those with snowstill packed inside the wheel spokes!

Yes, the metal valve stem cap did lookway “cooler” than the gray plastic oneit replaced. Unfortunately, it bondedcompletely to the valve stem over thecourse of a single salty winter. Ouch!

be on, the system would still be opera-tive. You would be guilty of making thesystem inoperative. If the system werealready inoperative (TPMS light flash-ing), would you knowingly be making itinoperative by installing the wheelswithout sensors? Looks like their answerwould still be not to get involved, al-though this particular circumstance wasnot discussed.

Oops. The regulation prohibits“knowingly” making the system or a de-vice or element of the system inopera-tive. NHTSA’s general stance is that ac-cidental, negligent or inadvertent dam-age is not included in “knowingly” mak-ing the system inoperative. May you re-turn the vehicle to your customer? Yes,unless you “knowingly” made the sys-tem inoperative. In that event, you mayallow it to be used solely “for testing ora similar purpose during maintenanceor repair.”

Dang. Once again, unless you have“knowingly” made the system or someelement of it inoperative, you’re notguilty of a regulatory infraction. Ofcourse, if an inoperative TPMS was the

customer’s original complaint, you canexpect some unhappy fallout. And if itwasn’t the original complaint, you mayat the very least want to add an inflationcheck to your final inspection routine.

Well, how did you do? I have to admitthat some of the answers surprised me,at least a little. I was pleased to learnthat no one is going to force consumersto make repairs to a system that is, in thefinal analysis, merely a reminder tocheck tire pressures. As to the snow tirequestion, my own experience has shownthat the folks who are most likely tospring for an extra set of winter tires andwheels are also the most likely to keepup with pressure checks in the winter,regardless of whether their cars haveTPMS. So the idea that I shouldn’t in-stall their winter wheels struck me asshowing perhaps more concern for theletter of the law than for the reality ofthe increased driving safety a set of goodsnows can offer. Still, you can’t win theargument, so you might as well acceptthe reality: If the TPMS system is ingood working order when the vehicle ar-rives, it should still be when it leaves.

ConclusionThe TPMS sensor replacement marketis poised for major growth. Most cus-tomers will respond to a lit TPMS light,at least checking with you to see if a sim-ple pressure check and adjustmentwon’t make things right. A light thatstays on or one that flashes is likely tomake most customers uncomfortableenough to spring for a new sensor, atleast the first time around.

The legal issues are fairly straightfor-ward, so play it straight. While NHTSAhas not announced plans for randomchecks or undercover sting operations,these remain within its potential rangeof action should field data indicate thatthey’re needed.

A fairly simple checklist is all youneed to ensure that you stay on theside of the angels. While the technicaldetails vary by year, make and model,the overall principles remain the samefor all vehicles.

TPMS SENSORS REACH RETIREMENT AGE

Circle #15

This article can be found online atwww.motormagazine.com.

28 June 2013