Professional_Tool_And_Equipment_News_March_2020 - 38

Let's talk TPMS
A look at the current state of TPMS and
the components, tools, and knowledge used
to service this important safety system.
By Scott Brown,
Contributing Editor

hile Tire Pressure Monitoring Systems (TPMS) date as far back as the
1980s when they first appeared on higher end European vehicles, their
increased use has been driven by the federal government beginning in
2000 when the Transportation Recall Enhancement, Accountability, and
Documentation (TREAD) Act was enacted. The TREAD Act was a result of investigations
into an abnormal number of tire failures involving Firestone tires installed on Ford
Explorer vehicles following several tragic vehicle events.
The mandate for TPMS in the
systems so that they're able to properly
U.S. came from the Department of
report trouble to the driver.
Transportation (DOT) in 2005. The fedThere are a couple of downsides to
eral regulation requires all 2008 model
using iTPMS, however. First, the system
year vehicles and newer under 10,000
is unable to identify and report which tire
gross vehicle weight rating (GVWR) to
is actually low. Second, if all four tires
be equipped with a tire pressure moniare equally low, the system will be unable
toring system that detects when one or
to alert the vehicle operator. As per the
more of a vehicle's tires is significantly
regulation, all TPMS are required to disunder-inflated and illuminates a low tire
play a driver alert warning when the tire
pressure warning indicator light.
pressure deviates by 25 percent from the
The events leading to the TREAD Act
recommended pressure.
were serious and resulted in brand damTechnicians need to be especially
cognizant of tire size when servicing
age for both Firestone and Ford Motor
Company. They primarily involved vehiiTPMS sensors.
"On iTPMS systems, one needs to be
cles with a high center of gravity that sufaware of the variance in tire diameters,"
fered tire failures that were linked back
says Matt Fanslow, technician and shop
to low tire pressure.
manager at Riverside Automotive in
TPMS SENSORS
Redwing, Minnesota. "We look closely
Today, there are two types of tire pressure
at the tire circumference before diving
monitoring: direct (dTPMS) and indirect
in on diagnosing these systems."
(iTPMS). A direct measurement system
TPMS sensors have their own batmeasures the tire pressure via a wiretery power supply and communications
less pressure transducer mounted inside
are usually handled by the same wirethe tire.
less receiver used for keyless entry. The
Indirect systems make inference to
wireless receiver typically communicates
tire pressure by measuring the rolling
tire pressure data via the CAN so that the
circumference via individual wheel speed
onboard systems can leverage that data
sensors. These are usually part of the
for safe vehicle operation. Sensors generanti-lock brake system (ABS). Basically,
ally transmit information once every 30
when the tire pressure is low, the rollminutes when parked. The update rate
ing circumference shrinks, resulting in
typically increases to about 1 Hz when
a shorter period of time per revolution.
the sensors can identify that the vehicle
is no longer at a standstill. For most sysAlgorithms are used to monitor these

PTEN

MARCH 2020

www.VehicleServicePros.com

tems, this threshold occurs at speeds
greater than 30 mph.
When replacing TPMS sensors that
are damaged, worn, or have low batteries, technicians can choose either OEM
replacements or universal aftermarket
units. There are reasons to consider
each option.
"We use Autel MX sensors unless
they [are not compatible], and then we
go OE," Fanslow says. "I would guess that
the Autel sensors [are compatible] about
95 percent of the time."
On the other hand, Kirk Holland,
owner of Gladney Automotive Solutions
in College Station, Texas, says his shop
uses OEM sensors even though universal
sensors are less expensive. He notes they
have had some sensors fail to learn IDs.
Thanks to the various options available on the market, it's becoming more
common to see older model vehicles
equipped with TPMS that have both
OEM and aftermarket sensors. This can
present a new challenge to technicians
servicing the vehicle.
"Twelve years into TPMS [being
government mandated] the chance
for a vehicle having multiple sensor
types installed is increasing," says Scot
Holloway, CEO and general manager
of Bartec USA. "Vehicles with a combination of OE and aftermarket sensors
present a unique challenge for the service
provider. Do they have the right service
kits or replacement parts to properly
service that car or truck? [For example],
early GM TPMS sensors only 'activate'
with a magnet, not a TPMS tool. The
technician needs to know this, otherwise they could get a false diagnosis of
a TPMS sensor."

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