BY MIKE MAVRIGIAN
Busting tires has served as an auto repair intro
for many aspiring techs. Tires have now gone
high-tech, and special tools and techniques are
required to avoid busting something expensive,
even during routine service.
S
hop owners and technicians
may have always considered
tire and wheel service to be the
low-tech aspect of their workday. But there’s some new
technology out there now that may
make you reassess that notion.
Tire Pressure
Monitoring Systems
A tire pressure monitoring system
(TPMS) alerts a vehicle’s driver of lower-than-specified tire inflation pressure.
If a vehicle is equipped with run-flat/zero-pressure tires, a TPMS is absolutely
needed, since most drivers won’t feel
the result of a low-pressure condition
when a run-flat tire loses pressure.
As of 2007, all OEMs will be required to feature a TPMS on their vehicles. This means that the aftermarket
service industry must be able to handle
these systems properly and diagnose
system problems.
Two types of tire pressure monitoring
systems are currently in use—direct
and indirect. A direct tire pressure
monitoring system features an individ-
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July 2006
ual sensor or monitor mounted inside
each wheel’s inner well. This system is
calibrated to alert the driver when one
or more tires have lost at least 20% to
25% of the programmed or recommended inflation pressure. A receiver
mounted in the vehicle receives individual wheel sensor signals, then sends this
information to a central on-board computer (ECU), which in turn alerts the
driver via an in-dash warning signal.
Whenever a low-pressure signal is
processed by the ECU, the in-dash tire
pressure warning light will illuminate.
In most cases, if a tire pressure problem
is indicated, the warning light will remain on constantly. However, if the
warning light blinks, this indicates a system fault that must be diagnosed.
If wheel positions are changed on the
vehicle (during the course of tire rotation, for example), individual sensors
must be reprogrammed. If the sensors
are not reprogrammed, the ECU will
then assign the pressure data to an incorrect wheel location.
Depending on vehicle make, model
and year, one of two direct-type TPM
Photoillustration: Harold A. Perry; photos: Mike Mavrigian and Wieck Media
21st CENTURY
TIRE SERVICE
sensor/transmitters may be present.
These are the banded type and the
stem type. Banded inflation sensors are
attached to the wheel’s inner well area
via both a peel-off positioning adhesive
and a circumferential band clamp.
Stem-type sensors mount at the valve
stem location, with the valve stem an integral part of the sensor.
Most OE tire pressure monitoring
systems are the stem type, partly to aid
in system diagnosis, since the sensor is
much more accessible, in terms of distance, by a diagnostic or relearn tool.
Band-mounted sensors are located
deep inside the wheel, making it more
difficult for the signal to pass to the diagnostic tool, whether the system uses
an RF signal or a magnetic signal.
Stem-type sensors weigh about an
ounce, so this presents no extraordinary
balancing issues.
The OE-favored direct type pressure
sensors are powered by a 10-year lithium battery. The expected battery life is
realistic, since these sensors are designed to operate only during or after a
20-mph speed is reached. When a vehicle is parked, the sensors are designed
to transmit pressure only once per hour
or so.
If a vehicle is equipped with an OE
TPMS and the customer wants a set of
aftermarket alloys, pay attention: Not all
aftermarket wheels will accept the
stem-type sensor. These sensors require
a specific valve hole relief design. Most
aftermarket wheels, which are designed
to accept only standard snap-in rubber
valves, do not allow the addition of the
stem type transmitter. In this case, you’ll
need to find aftermarket wheels that are
designed to accept stem-type sensors.
Instead of incorporating a stem-type
direct system, some vehicles rely on information already monitored by the antilock braking system (ABS). This is referred to as an indirect TPMS. Since
an insufficiently inflated tire will rotate
at a different rate than a properly inflated tire, due to the resulting difference
in rolling tire diameter, the difference in
wheel rotation is sensed by the ABS. A
signal is then sent to alert the driver via
a warning light. It’s then up to the driver
to check all four tires to determine
which one is underinflated.
However, if all four tires are equally
July 2006
39
Photos: Mike Mavrigian
21st CENTURY TIRE SERVICE
This is a typical stem-type tire pressure sensor/transmitter installation. It’s essential that the wheel’s inside well
area is clean to prevent contamination of the sensor.
underinflated, the ABS might not trigger the pressure warning, since all
wheels would rotate at the same speed.
Indirect TPMSs generally are designed
to illuminate the warning light when a
single tire’s pressure has dropped by
about 30% in relation to its official recommended inflation pressure.
Aftermarket Systems. The three
commonly available aftermarket tire
pressure monitoring systems are made
by Doran, Smar Tire and Schrader.
Doran’s PressurePro systems are
available to suit a wide variety of applications, including passenger vehicles, lightto heavy-duty trucks, motorhomes, fifthwheel trailers and tag trailers. The PressurePro installation kits include a dashmounted 12-volt monitor and individual-wheel sensors that thread onto each
wheel’s air valve. An audible alarm alerts
the driver if any tire loses more than
12% of its programmed pressure. A simple programming procedure is outlined
with the kit’s instructions.
Smar Tire’s system includes four
band-mounted wheel-mount pressure
sensors and a dash-mounted receiver/
display unit. Each pressure sensor
weighs a tad under 1.5 oz. These sensors
are said to be accurate to ⫾1.5 psi. Sensor mounting band-straps accommodate
13- to 20-in.-diameter wheels. The band
is clamped to the wheel’s inner well
area. Each sensor features a motion detector that powers the sensor down
when the vehicle is parked, conserving
40
July 2006
Be careful when dismounting or mounting tires on a wheel
that’s equipped with a TPM sensor. Some OEMs recommend
removing the retaining nut and dropping the sensor into the
wheel before attempting bead-breaking or dismounting.
the lithium sensor’s five-year battery life.
The basic receiver display identifies
each tire by a color-coded light. Each
sensor is also color-coded, as is each tirevalve-mounted washer. The sensors are
programmed to alert the driver if tire
pressure drops to 22 psi. If pressure
drops below that, a red LED on the display illuminates above the individual color-coded indicators. As an additional
alert, if air pressure drops to 18 psi, a
second-level warning activates an audible alarm, and the LED will flash red.
Schrader’s Generation II Smart Valve
RF TPMS is a direct system comparable
to OE systems. Individual stem-type
sensors mounted to each wheel transmit
data to individual wheel-well-mounted
detectors, which in turn send signals to
the centrally mounted receiver.
TPMS Initialization/Diagnostic
Tools. A test tool is required to service
any direct TPMS. For aftermarket use,
easy-to-use hand-held testers are commonly available. The two most common
uses for a diagnostic tool are to perform
a system reset and to test system operation. About 75% of the tool’s use will be
for resetting during routine tire or
TPMS service.
There is no industry standard regarding TPMSs. Some systems require resetting if primary vehicle battery power
is interrupted, while this problem is not
an issue in other systems. Depending
on vehicle make, model and year, some
systems’ data may be corrupted if the
ignition key remote control is activated
during a pressure sensor reset procedure. Currently, more than 40 different
testing and resetting protocols are in
use. Some aftermarket initializing and
diagnostic tools are make/model/yearspecific, while others are designed to
communicate universally with a broad
spectrum of OE tire pressure monitoring systems.
Sensor Replacement Caution. Before installing any direct (stem-type)
TPMS sensor, and before mounting a
tire onto a sensor-equipped wheel, you
must note the sensor’s ID code (printed
on the sensor body). This code will be
required when programming or reprogramming the sensor. Remember to
record this number before hiding the
sensor from view.
While specific procedures for initializing an indirect TPMS may vary among
vehicle makes and models, a typical approach involves first adjusting each tire’s
inflation pressure to the recommended
level. With the vehicle stopped, turn the
ignition switch to the ON position. Press
and hold the tire pressure warning reset
switch (typically located under the dash)
until the tire pressure warning light
blinks three times at 1-second intervals.
Next, operate the vehicle at 19 mph or
more to complete the initialization of
the skid control ECU. If the tire pressure warning light blinks at .25-second
intervals while the vehicle is in motion,
the initialization may have failed. If this
Photo: Mike Mavrigian
Photo courtesy SPX/OTC
21st CENTURY TIRE SERVICE
This hand-held initializing tool is being used to reprogram
a sensor for wheel location. This procedure can be accomplished with the tire on or off with stem-type sensors.
occurs, the initialization procedure must
be repeated. After initialization is completed, the skid control ECU monitors
tire pressure by using the ABS/traction
control wheel speed sensors.
The Cool Tools. Bartec, a manufacturer of TPMS tools for both the OE
factory and dealership levels, offers a
variety of hand-held TPMS service tools
that are dedicated to specific makes
and/or systems. In addition to their OE
support, Bartec offers two hand-held
tools specifically designed for the aftermarket—the DBL3 and the DEG.
The DBL3 is an entry-level sensor
“trigger” and test tool. The DEG is a
heavy-duty trigger, test and diagnostic
tool that features a large, easy-to-view
display. These tools are able to test sensor condition (capturing sensor ID number, temperature, pressure and operating data from the sensor’s internal clock,
and decoding this information while determining sensor status). Such higherend tools can “force” a sensor to transmit data, without the need to perform a
driving loop. Bartec also offers three
versions of diagnostic tools for both aftermarket and dealership use.
Diagnostic tool leader OTC offers its
Model 3833 Tire Pressure Monitor, a
convenient hand-held device that provides total and universal monitoring of
all OE stem-type TPMSs. Simply enter
the vehicle make, model and year and
the tool readies itself to diagnose or re-
42
July 2006
The diagnostic/relearn tool is placed adjacent to the tire
pressure sensor, accommodating communications via either an RF or magnetic signal, depending on OE design.
set any system. A comprehensive manual and CD are also available.
When performing troubleshooting
and diagnostics, the tool is able to activate the sensors and inspect all transmitted data, which is displayed on the
monitor screen (ID number, pressure,
last-vehicle history, etc.). The tool is easily updatable by connecting it to a PC
for downloads from OTC.
Also available is the T.I.P.S. (Tire Inflation Positioning Switch) tool from
Spectrum Composites. This universal
LED sensor resetting tool is designed
only to reset/initiate system sensors. According to the maker, the tool is compatible with all current OE tire pressure
sensors. A working relationship between OTC and Spectrum Composites
was announced recently.
TPMS Service Guidelines. Any
good shop should have no trouble servicing a tire pressure monitoring system, so long as the following guidelines
are adhered to:
1. Handle with care. When a system
problem occurs, chances are a damaged
or faulty sensor is the cause.
Because of its location (close to the
bead), the prospect for stem-type sensor damage is high as a result of curb
hits or careless handling during tire
changing. In the case of a band-mounted sensor, damage can easily occur during tire changing, especially if the technician isn’t aware of the sensor’s pres-
ence. While some band-mounted sensor setups feature a color-coded valve
stem washer or cap, some don’t. Play it
safe and ask the customer if the wheels
are equipped with a tire pressure monitor, since a band-type system may have
been retrofitted to the wheels.
The need for caution should be obvious, but we must stress the importance
of exercising care during tire dismounting and mounting. A pressure sensor
can be easily damaged by a tire iron, so
avoid blindly jamming anything into the
bead or well cavity. Most OEMs specify
that the stem-type sensor be dislodged
before attempting bead breaking. Deflate the tire first, then remove the sensor’s retaining nut. Gently allow the sensor to drop into the tire cavity. This
moves the sensor out of danger during
bead breaking and dismounting. As
soon as the sensor is accessible, remove
it from the tire and set it aside.
Note: Before reinstalling a sensor, always record the ID number, as this may
be needed during the initialization procedure (although some sensor tools are
able to recognize the ID number automatically).
Never tighten the retaining nut on a
sensor by guessing at torque value. Take
the time to reference the OE torque
value specification, and follow this value
in every case, since overtightening can
damage the sensor.
2. Not just any replacement part will
do. The advent of the TPMS changes
several service procedures, and valve
core replacement is one of them. Most
stem-type pressure sensors feature alloy
or plastic valve caps and nickel-plated
cores. In many cases, the tip of valve
stem may act as the sensor’s data-transmission antenna. Whenever replacing
valve cores or caps, use only the type
originally featured by the OEM.
3. Use precise pressure. Make sure
your pressure gauges are accurate when
checking inflation on any TPMS. The
OE-level pressure sensors can be surprisingly sensitive (sometimes alerting
the system when the tire is underinflated by only 2 psi or so).
4. Don’t ignore the remote. Depending on the vehicle make and model, the
key fob remote control may be involved
in resetting procedures. Be aware of
this, to avoid inadvertent button-pushing on the remote, which may initiate a
reset.
5. When to reset? Resetting a TPMS
is required if certain procedures are
performed, including tire pressure correction(s), tire/wheel rotation, tire or
wheel replacement, TPMS sensor replacement, receiver antenna replacement, TPMS control unit replacement
or loss of vehicle battery power.
Photo courtesy RTI Technologies, Inc.
21st CENTURY TIRE SERVICE
Depending on how much tire service
your shop does, a nitrogen-generating station may make sense. After
the initial cost of the unit is recovered, extra revenue can be “generated” from premium tire service
that includes a nitrogen fill.
The big news in the tire industry today
seems to involve the use of compressed
nitrogen to inflate tires. This inert,
moisture-free gas has been used for
decades by the racing community (as
well as for aircraft, military and various
industrial applications). The primary
reason for using nitrogen is simple and
twofold: It’s an attempt to maintain a
consistent inflation pressure, because
since a near-pure fill of nitrogen features “fatter” molecules than an air mixture, a nitrogen-filled tire will leak less.
Nitrogen doesn’t contain or carry airborne moisture. Think about it: When
moisture-laden air heats, it expands;
when it cools, it contracts. On a warm
day or when a tire is heated by use at
high speeds, the inflation pressure rises.
When the tire cools, inflation pressure
drops. By using nitrogen instead of air,
the initial inflation pressure is much
more stable. This means that the tire
On the PAX tire system, an inner liner is positioned onto the wheel’s inner well to provide tire-to-wheel integrity under low- or no-pressure
conditions. Servicing this wheel and
tire combination requires special
tools and techniques.
44
July 2006
Photo courtesy Michelin
Nitrogen Tire Filling
contact patch remains more stable in
spite of thermal influences.
Some promotional material regarding nitrogen, while true, seems to exaggerate the issue. For instance, using nitrogen “increases tire life”; yes, because
inflation pressure is more stable. Nitrogen provides “better handling and braking”; yes, because inflation pressure is
more stable. Nitrogen “provides better
fuel economy”; again, yes, because inflation pressure is more stable. Let’s keep
things in perspective: Nitrogen doesn’t
save tires; proper inflation pressure
saves tires. Whether we accomplish this
by the use of nitrogen or regular pressure monitoring is the real issue.
Because, as we said, nitrogen molecules are larger than molecules that
comprise air, nitrogen leakage is about
one-sixth that of compressed air. Also,
nitrogen runs about 20% cooler than
compressed air, theoretically resulting
in diminished tire degradation. Nitrogen is also a poor heat conductor, which
is one of its benefits. It won’t cause inflation pressure changes due to temperature fluctuations. To achieve the maximum benefit of inflating tires with nitrogen, a charge should consist of at
least 95% nitrogen.
Compressed nitrogen is commonly
available at any compressed gas supply
facility. Nitrogen cylinders are available
in five sizes, based on cubic foot capacity. From smallest to largest, these include sizes R, Q, S, K and T. One option
is to visit your local gas supplier and rent
the size and number of nitrogen cylinders you’d like. When the cylinder is depleted, exchange it for a full cylinder.
The only other pieces of equipment
you need are a regulator (which threads
into the cylinder port and allows you to
dial down the outgoing pressure to a
manageable level—say, 100 psi) and
one or more safety devices to prevent
the regulator from being damaged. You
can install a safety cage on the cylinder
top (this houses the regulator, protecting it from damage). You can (and
should) also secure the standing cylinder against a shop wall to prevent it
from being knocked over. Compressed
nitrogen cylinders are charged at 2200
to 2640 psi, so common sense should
tell you that if the regulator is damaged
and an open release is created, a nitrogen cylinder will become a missile that
can shoot across the shop floor.
Nitrogen is an inert gas, and as long as
it’s regulated to a sensible pressure level,
any quality serviceable hose and hose
couplers will work just fine. If you want
to follow the current trend in terms of
color designations, you can buy green
21st CENTURY TIRE SERVICE
Photo courtesy Hunter Engineering
The tire and
PAX inner liner
shown here
are being
installed on a
wheel. Special
tire machine
rollers
prevent liner
damage
during tire
removal and
installation,
and the inner
bead must be
installed by
hand with PAX
bead levers.
hose. Green valve caps are a good idea
as well, for no other reason than to readily identify a tire that has been inflated
with nitrogen. Be aware that while most
nitrogen-generating systems offer green
valve stem washers and caps, some manufacturers may offer their own unique
color. Purigen98, for example, uses blue.
The only reason to color-code the valve
caps is to alert a shop that the tire has
been inflated with nitrogen. If a nitrogen-filled tire is topped off with compressed air, no damage will occur. You’ll
simply diminish or lose the benefits that
a near-pure nitrogen fill provides.
So, you have a choice, depending on
your mood. You can either purchase a
nitrogen-generating system that allows
you to “make” your own never-ending
supply of nitrogen, or you can rent compressed nitrogen cylinders. Remember,
if you rent cylinders and your anticipated use is relatively low, you’ll save money. If you purchase a nitrogen generator,
you won’t need to worry about running
out of the stuff.
The PAX Tire System
The PAX tire system, developed by
Michelin, is a unique so-called run-flat
tire and wheel system consisting of a
special wheel, an inner liner, a specialdesign tire and a TPMS sensor. The intent is to provide tire-to-wheel integrity
under low- or no-pressure conditions.
This is accomplished by two basic features—how the tire “bead” seats and
locks to the wheel rim and the presence
of a reinforced polyurethane inner liner
46
July 2006
Tire Service
Tool Sources
Bartec Auto ID LTD (tools and info)
U.S. Office: 586-685-1300
www.bartecautoid.com
SPX/OTC
800-533-5338
www.otctools.com
Spectrum Composites, Inc.
800-359-9855
www.tipstool.com
that provides support in the event of
pressure loss. This inner liner is positioned onto the wheel’s inner well, but
is not affixed to the wheel. The wheel
front (outboard) diameter is smaller
than the inboard diameter, allowing removal of both the tire and support ring
liner past the smaller-diameter outboard side of the wheel. The liner must
then be removed from the tire in a separate procedure.
The way in which the PAX tire seats
onto the wheel provides a positive lock
that prevents the bead from unseating
even in a zero-pressure condition. Instead of the bead being held captive behind a rim flange (anchored only by relying on internal pressure), the PAX
bead seats into a recessed groove in the
wheel rim. As internal air pressure decreases, the vertical load between the
bead and wheel actually creates a more
secure bead-to-wheel anchor.
The inner liner (also called a support
ring) is somewhat flexible while creating a supportive gap-filler between the
tire and the wheel well. This provides
support and maneuvering control even
after a complete loss of pressure.
This highly advanced run-flat system
is original equipment on late-model
Honda Odysseys and a few high-end
rides in Europe, and is employed on
many high-risk armored/securityequipped executive and government vehicles. More applications are being
added.
To dismount or mount a PAX system
package, specific equipment and procedures are required, involving two
separate service issues—removal/installation of the tire from/to the wheel;
and removal/installation of the inner
liner from/to the tire. In other words,
the PAX system requires two separate
tasks involving either dismounting or
mounting.
Basically, mounting a PAX package is
a four-step procedure:
1. Remove tire assembly from wheel.
2. Remove inner liner from tire.
3. Install inner liner to tire.
4. Mount tire to wheel.
Regarding service equipment needed for dismounting and mounting a
PAX tire/wheel assembly, you have a
choice of buying a dedicated changer
specifically designed for the task or an
accessory kit that adapts your current
changer to handle the PAX system.
Considering the number of PAX jobs
that your shop may encounter, the volume may not justify the price for a
piece of equipment that can’t handle
conventional wheels/tires. The sensible
approach seems to be the adapter kit.
Check with your equipment maker to
see if they offer such kits for your
shop’s tire changer.
Will you see tons of PAX type systems roll into your shop? Probably not,
at least not right now. However, you
need to be aware of the service issues in
order to avoid damaging these wheels
and tires if conventional changer procedures are inadvertently followed.
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