The Challenge of TPMS

First, a little history: TPMS (Tire Pressure Monitoring System) was introduced in Europe as an option on some luxury vehicles in the 1980s, such as the Porsche 959 in 1986. The Renault Scenic in 1999 used a system developed by Michelin. In

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United States, TPMS was introduced after the passage of the TREAD Act under then-President Bill Clinton. It mandated the use of TPMS systems in all light motor vehicles. The idea was that TPMS would alert drivers to when their vehicles had dangerously under-inflated tires and thereby prevent roll-overs or tire blowouts that could result in fatalities to driver and passengers. By 2008, all new vehicles sold in North America were mandated to have TPMS systems.

At its core, TPMS technology is simple, made up of four key components: a sensor in the wheel, a body control module, a receiver/antenna and a display icon.

Inside each wheel on Direct TPMS (the most common type of TPMS) the wheel sensor measures tire pressure and temperature inside the wheel and then the TPMS sensor transmits the data to a receiver and eventually the body control module, which then transmits that data to the driver through a dashboard display.

From Simple to Complex

Andy Forsberg, OTC Electronics Product Manager, Service Solutions LLC says many TPMS systems can be, in this own terminology, “simple or smart.”

A simple TPMS system would tell the vehicle owner a tire or tires have fallen below an acceptable threshold of pressure, for example, or are dangerously above that threshold, but will not tell the driver which tire or tires are the ones with the problem. The owner has to get out their trusty tire pressure gauge from the glove compartment (which every vehicle owner should have) and test the individual tires until they come across the ones with the problem.

“On the ‘smart’ systems, the technology takes the guesswork out of TPMS,” adds Forsberg. “If there is a sensor reporting, the ‘smart’ system is going to tell the vehicle owner what tire that sensor is on, so the driver or the service technician does not have to go around and make a guess which tire is the problem. A tire that is 10-15 per cent too low in pressure is not obvious visually.”

Now this is where things get a little complicated.

Each sensor emits a unique ID number that it transmits to the vehicle’s electronic TPMS systems. The reason for this is to prevent ‘cross-talk’ amongst the sensors. Try to imagine if the same make and model year of vehicle pulled up beside you at a red light or stop sign. If the TPMS sensors did not have unique ID numbers it is very likely your onboard TPMS would register the other vehicle’s tire pressure and temperature information, say that the other vehicle’s left-front tire is low on pressure. But you would not have a way of knowing that and assume that your vehicle’s tire pressure is low.

It is important to remember this piece of technical information because it is the reason why the TPMS systems have to be programmed or set to re-learn when tires are rotated or TPMS sensors are replaced.

“Each sensor has its own digital ID, frequency and protocol,” adds Scot Holloway, general manager with Bartec USA, LLC, a maker of TPMS tools. “The sensor ID, in particular, must be recorded or programmed to the vehicle in order for the TPMS to work properly. Every time a sensor is replaced, the ID must be programmed/re-learned to the vehicle.”

This is critical for vehicles that have the ‘smart’ TPMS systems that OTC’s Forsberg mentioned earlier. Since these vehicles monitor the tire’s pressure and temperature, along with their locations, the onboard TPMS systems have to re-learn the location of the sensors if the tire positions changed, or that a new sensor has been installed to replace a failed sensor. So what happens if that is not done? Well, the vehicle owner will still be able to drive their vehicle. But when that vehicle registers a problem with a tire, the vehicle owner will be given the wrong information as to where that problem tire is located. It’s not too hard to understand how that would happen.

If the on-board system knows that a particular sensor is located on the front-left tire that is how it will display that senor’s information to the driver on his or her dashboard. But if that tire is moved, the on-board TPMS will still register the tire at being located at the front-left position even if the tire is now located somewhere else on the vehicle. The on-board TPMS uses the sensor ID simply as a means of saying “That unique ID is for the front-left tire,” to the vehicle owner. If it moved, it has to re-learn the location of the sensor’s ID, or it will continue to tell the vehicle owner that the sensor is located on the front-left wheel even though it has moved, say to the passenger side of the car.

Forsberg says one can see this problem with some rental vehicles using TPMS if the tires have been rotated, but the technician did not re-learn the system.

“I will get a notice that there is a low-pressure warning in front-right tire,” he says, “but when I pull into a gas station to fill that tire, it turns out to be 10-15 psi over-inflated. In fact, it is the left-rear tire that is low.

“What has happened is that the vehicle was not taught that the position of the tire and sensor has changed. It still believes that the sensor is reporting a low-pressure situation from the front-right position.

“Drivers will take the wrong information being given to them and add air to an already properly inflated tire, soon making the tire dangerously over inflated.”

Always be Ready to Re-Learn

Just as each sensor has a unique ID, vehicle makes and models have their own re-learn procedures. Bartec USA’s Holloway says there are three common resetting or re-learn types today:

Stationary

— 29 per cent of vehicles uses this method, also known as “On-Board.”A TPMS activation tool is required with the car in “re-learn” mode. New IDs can be programmed without driving the vehicle.

OBDII

— 35 per cent of vehicles uses this method, also known as “scan tool” method. A combination activation and scan tool is required to program new sensor IDs into the vehicle. New ID’s can be programmed without driving the vehicle.

Auto-Learn

— 36 per cent of vehicles uses this method, also known as “drive in” method. A vehicle can learn a single new ID and in some cases multiple new IDs without the use of a tool. It requires driving the car in order to turn off the light.

“Less that 40 per cent of the vehicles can reset themselves,” Holloway adds. “Some ‘Auto-Learns’ can only do one new TPMS sensor at a time, or it takes a lot of driving.”

What that means is that a shop doing tire changes, rotations and sensor replacements will need to invest in a combination of scan tools and activation tools.

Both OTC and Bartec USA offer a combination of TPMS tools and activation tools. OTC offers an activation tool that works with its popular Genisys scan tool, along with a library of easily accessible re-learn procedures for the many vehicle makes and models on the road through the Genisys tool. Bartec USA offers the Tech300SD, an activation tool and the more advanced Tech400SD activation and scan tool combination.

For service shops, the investment in these tools is going to be critical to capture tire business, especially in two areas. One big growth area will come from the simple fact that TPMS sensors have to be replaced when their on-board battery runs down, as the battery cannot alone be replaced.

It is sealed so the whole sensor has to be removed and a new one installed. With many sensors now nearing the end of their battery lives, there is going to be a booming business in service shops replacing these sensors and then having to re-learn the vehicle systems once those new sensors are installed.

Another is the simple fact that sensors can and often are neglected by vehicle owners, so they will have to be replaced. This is going to be where your shop’s technicians patience and training will come in handy.

“The sensors have consumable parts that need to be replaced each time the tire is serviced,” Holloway says. “This will help insure that proper sealing is maintained, and limit the amount of corrosion. Also, using the proper replacement parts is critical. Use only new nickel plated valve cores to prevent galvanic corrosion.

“Always use a plastic dust cap to also limit corrosion. When properly maintained, the sensors should last five to seven years, before battery failure. At which point the entire sensor must be replaced.”