Quite simply, a tire pressure monitoring system (TPMS) is an electronic system designed to monitor the air pressure in a vehicle tire and automatically transmit a warning to the driver in the event of an under- or over-inflated tire.
These systems report real-time tire-pressure information to the driver of the vehicle, either via a gamiuge, a pictogram display or a simple low-pressure warning light.
Due to the TREAD (Transportation Recall Enhancement, Accountability and Documentation) Act, all vehicles manufactured during 2008 or later are required to have a compliant TPMS system on board. The final rule requires that the driver be given a warning when tire pressure is 25% or more below the vehicle manufacturer’s recommended cold tire inflation pressure (placard pressure) for one to four tires.
While law makers and tire makers are quick to sing the praises of TPMS, as a technician or shop owner, you know that this amazing technology comes with its fair share of headaches and problems relative to diagnosis, repair and maintenance of these systems.
The following article will attempt to offer some general guidelines on making buying decisions and provide an overview of what types of products are available to make your life a little easier when working on TPMS.
Without spending too much time talking about evolving technologies, we need to cover “current state” versus “desired state” in terms of TPMS architecture; specifically the sensors and their power supply.
From the beginning, the prevailing design for TPMS sensors has included a sensor and a battery incorporated in a box inside the wheel. The designs vary from supplier to supplier, but the general concept is the same. This design describes 95-98% of the TPMS sensors in use today on passenger cars and light trucks.
The sensor inside the wheel continuously reads tire pressure and reports it back to the vehicle’s on-board diagnostic system. The system constantly compares the pressure values from all four wheels. The system also monitors and evaluates information such as vehicle speed, wheel rotation speed, ambient temperature, tire temperature and chassis height. All of this data is used to evaluate if the tire pressure is within safety margins as prescribed by the OEM and tire manufacturer.
This current design, while fairly rugged and functional, has a few drawbacks. Early on, these sensors caused problems for tire and wheel manufacturers due to clearance issues. Low-profile tires can create nightmares when mounting or demounting. Many a technician has trashed a sensor when “fishing” for the bottom bead during a demount.
Over time the sensors have gotten smaller, wheel service equipment manufacturers have developed new tools and equipment, and technicians have learned new processes to deal with TPMS sensors.
The “desired state” would be a sensor that doesn’t need a battery or one that uses a battery that lasts an extremely long time. Advances in battery technology have allowed sensor manufacturers to come up with a design where the battery resides in the wheel stem on the outside of the wheel. This is fantastic for you as a service provider, as it allows you to diagnose and replace dead batteries without demounting and remounting tires. This means less time chasing ghosts, less chance of wheel damage and more productivity for your shop!
The second design, which sounds a little like make-believe, is sensors that can broadcast a signal to the car’s control system without the need or use of a battery. The good news is that both of these designs are already in some new vehicles or are very close to being released.
The main issue for you as a technician relative to installing and removing TPMS sensors, is to do it quickly without damaging the sensor in the process. One tool that is handy to have in the shop is a “fishing tool.” This tool, also known as an installer or puller, allows the technician to pull the stem of the sensor up through the hole in the rim. This can be an especially difficult job on low-profile tire setups. By screwing the fishing tool into the stem, you are able to get enough leverage to pull the sensor into place.
You will also want to invest in a good quality 1/4” drive “inch-pound” torque wrench. This is used to attach the sensor to the rim with the correct amount of torque. This is critical to avoid damage. It is a good idea to document the torque reading on the work order when replacing sensors. This protects you and makes claims easier with your parts supplier.
You also need to have a selection of specialty sockets for removing the retaining nuts on the sensors’ stems, such as flip sockets with two different sizes on each socket.
The valve cores on TPMS are super critical and easily damaged. You can protect yourself by having a good selection of valve core removal tools. A couple of sizes should cover most stems.
One final tool that is a must-have is a valve core torque wrench. This micro torque wrench assures you install the valve core correctly.
Some of your time as a technician will be taken up “fixing” TPMS units. This includes replacing valve cores and tightening/replacing hardware, as well as replacing sensors. There are many good kits available that include an assortment of repair parts. These kits are a great investment for shops that are doing TPMS repair and service. Many a good-paying job can be sabotaged waiting for the parts store to bring you a $2 valve core! While there is a significant number of different TPMS sensors used on vehicles, there are some common ones that you might consider stocking if your shop plans to do a large volume of wheel and tire service.
There are three basic types of non-mechanical activities you will be doing relative to diagnosing and repairing TPMS. These are: Identification, Teaching (activation) and Scanning.
Identifying the presence and function of a TPMS sensor is accomplished by “reading” or testing for a signal from the wheel(s). Most TPMS tools can perform this function. These tools will verify the signal and report back to you the sensor type and the serial or registration number for that sensor. This data is required to be recorded in most cases when servicing TPMS. Be careful when buying a TPMS tool. Look for a tool that displays the sensor part number. A part of identification is being able to look up sensors by vehicle year/make/model. Make sure the tool’s data can be updated for future model years.
The really good TPMS tools can do a couple of other things that will make your life much easier. One is the ability to ignore non-TPMS signals. There are lots of things in a shop that can “fool” a tester. One common culprit is the keyless key fob. This little modern miracle is the Typhoid Mary of RF signals; causing false signals for some tools. Ask your tool dealer if the tool you’re interested in has signal discrimination. Along this same line of thinking, the really good tools can tell you if you are “talking” to the correct sensor for the car and type of activity (relearn or initializing) you are working on. While I am sure it has never happened to you…I have it on good authority that it is common for technicians to complete a job just to find out they just programmed the TPMS sensor on the vehicle in the next bay…OK, that’s just funny — unless it happens to you!
This is the most common and basic activity. You need to teach or reprogram sensors to tell them where they live. You have to identify the car and wheel position. If you are going to be doing tire rotation and balancing on 2008 and later vehicles, you don’t have a choice about purchasing a TPMS tool.
There are going to be times where you need to communicate directly with the vehicle’s Electronic Control Unit (ECU). In order to do this, you need a tool that includes an OBD connector. This allows you to easily and quickly “hook up” and communicate with the car’s system. Some things to consider are display type, navigation controls, printer capable, cable length, power supply and tool storage.
Display Type — The trick here is to get the biggest little display you can find. What I mean is you want a tool that is easy to handle and hold with one hand, but with the largest and brightest display you can find. Ask your distributor to show you the display. Does it have back lighting? How about adjustable brightness or contrast? Can you read it in bright sunlight as well as low light conditions? If you’re like me, you struggle to see in low light conditions, so make sure you can work with the tool.
Navigation Controls — How do you navigate the tool? Are the buttons hard or soft (on-screen)? Can you operate the tool with one hand? Is it logical to navigate the tool? Can you find the screens you want without a million clicks or moves? Check the tool out closely before saying “I Do.”
Printer/Output — Can you print your results? Does it have a wireless interface to a printer? Does it have a printer port? Can you download results to your PC? All of this is critical to be compliant and also for warranty work. The tool is no good if you can’t use it to get paid!
Cable Length — Is the cable long enough to let you plug into the OBD port and take the tool out to the fender? Can you comfortably sit in the driver’s seat and read the tool without being bent over? Can you use the tool safely on a road test? These are all good reasons to have a longer cable.
Power Supply — This is biggie. Does the tool run on AC, standard batteries or is it rechargeable? Each of these power types has pros and cons. Only you can decide which power supply you want, but make sure you take a look and decide what is right for you.
Tool Storage — This isn’t a deal breaker when purchasing a TPMS tool, but it’s worth knowing what the tool comes with. Some have nice blow-molded cases with room for accessories and sensors. It’s nice to have everything in one kit. This is especially true if the tool is a shop purchase, and you want to make sure you keep everything together.
Hopefully you now know a little more than you previously did. If you’re in the market for a TPMS tool, or will be soon, do your homework before the tool man is standing in front of you. There are some great tools out there to help make your job easier!
For more TPMS information, search for TPMS on www.TechShopMag.com, under Tech Articles, or visit our sister site, www.tirereview.com and click TPMS under the inTires header.