Tire pressure monitoring system (generally referred to as TPMS or TPM) is relatively basic in terms of the number of involved components. The pressure sensor transmitters (one transmitter mounted inside each wheel) monitor inflation data and send a FM radio signal to the system’s antenna and receiver, which then sends a digital signal to an ECU. Note that some vehicles may be equipped with one central antenna, while others feature individual antennas in the wheel wells at each corner.
A “direct” tire pressure monitoring system (where a dedicated system exists that monitors actual tire inflation pressure) is generally calibrated to alert the driver when one or more tires has lost at least 20-25% of the programmed/recommended inflation pressure. An “indirect” system relies on tire diameter changes (via ABS wheel speed sensor readings) to alert the driver of tire pressure changes. The indirect system is long-antiquated.
All new vehicles (2007 and newer) are federally mandated to feature TPMS in vehicles of 10,000 pounds gross vehicle weight (GVW) or lighter.
If a “fault” signal is processed by the ECU, the in-dash tire pressure warning light will illuminate. Generally speaking, if a tire pressure problem is indicated, the warning light will illuminate constantly. If the light blinks (in most OEM systems), this indicates a system fault that must then be diagnosed with the proper diagnostic tool.
It’s important to note that whenever sensors are moved to new locations (during wheel rotation, etc.), the ECU must be reprogrammed (reset/relearn) in order to maintain correct location information for the system ECU. Otherwise, each sensor may transmit correct inflation data, but the ECU will then assign the pressure data to the wrong corner(s) of the vehicle. For example, if a vehicle is equipped with dash information that identifies each specific wheel location, you may see a warning that the left front tire is low, when in fact the low pressure problem may be found at the right rear (because the wheels were rotated and the sensors were never reset). Each sensor has a unique ID embedded in its pulse signal. The ECU receives this pulse signal and assigns — remembers — the sensor’s wheel position.
Depending on the maker’s design, these wireless pressure sensors transmit their data to an ECU using either 315 Mhz or 434 Mhz FM signals, usually in the 125 kilohertz range (Most domestic-brand vehicles will utilize 315 Mhz, while most import-brand vehicles will use 434 Mhz. An exception is Nissan, which uses the 315 Mhz signal.)
Stem-type sensors are light, weighing in the neighborhood of about an ounce, so this won’t be a problem regarding wheel balance compensation.
The direct type pressure sensors are powered by a lithium battery, with an estimated life of five to seven years, depending on your information source (I’ve heard estimates as high as 10 years). However, since the use of these sensors is relatively recent, we really don’t have enough real-world experience to more accurately estimate battery life. The sensors are designed to “wake up” via centrifugal force (once the wheels rotate at about 20 mph or so). In order to help extend battery life, the sensors “go to sleep” when parked. In operation, the sensor produces a pulse signal in timed intervals (depending on the specific system) of every 30 seconds or every 60 seconds, etc. This also aids in extending battery life.
Service and maintenance
Traditional valves (prior to TPMS) are routinely replaced during any tire change. Stem rubber, the grommet area, and valve core seals age and become brittle or weakened. Besides, valves are cheap, so it just makes sense to install a fresh one when the opportunity arises. However, when it comes to TPMS (clamp-on or snap-in styles), many techs may be afraid to tamper with them. As a result they are often ignored. We need to recognize that in terms of sealing rubber components, nothing has changed…grommets, core seals and cap seals are still prone to gradual deterioration and should be replaced when needed. Service kits are available.
For clamp-on styles, this involves replacing the valve core, valve grommet, valve nut and valve cap. TPMS valves require a nickel-plated core. The use of a non-nickel plated core can lead to electrolysis (galvanic corrosion), which can result in the need to replace the entire sensor assembly. The nut used on clamp-on sensors is treated with a bonded lubricant that aids assembly, allowing the proper torque value when tightening the nut (which seats the grommet to the wheel). The valve grommet is subjected to compression force as well as high wheel temperatures. The need for periodic replacement should be obvious. The valve cap provides protection from moisture and other road contaminants, as with any wheel valve.
If the sensor is the snap-in type, the rubber valve body can be un-clipped from the sensor and replaced easily (new rubber body, core and cap).When it comes time to mount another tire, make a point to replace these components.
As we all know, designed torque values are assigned to every threaded fastener, regardless of size, application or location. Well, tire valves and TPMS components are no exception. The valve core should be tightened to a value of 4 in-lbs. Granted, most folks simply snug ‘em down until they “feel” good, but especially with a TPMS, you need to make certain that you’re following the correct procedures (if for no other reason than to protect yourself from a liability standpoint).
Invest in a dedicated core tool that features a preset torque function. Really — this is important.
On clamp-on sensors that feature a Torx screw (securing the valve to the sensor), the torque value will generally be about 11.5 in-lbs (check with a service manual). On clamp-on style sensors, the valve nut tightening value will vary depending on the specific make/model/year application, so check with the service manual (values may range from about 35 to 80 in-lbs).
In order to service any direct TPMS, a testing tool is absolutely required. At the OE level, these calibration/resetting/diagnostic tools range from hefty handheld units to large stationary pieces of equipment. For aftermarket use, easy-to-use hand-held testers are readily available. You don’t have a choice, by the way. If you plan to stay in the tire and wheel business, you must be able to reset and troubleshoot TPMS. If you haven’t purchased a tester yet, you’re wasting valuable time.
Service cautions and tips
Exercise care during tire demounting to avoid sensor damage caused by a tire iron. In other words, don’t blindly dig into the wheel cavity. If the wheels are equipped with OE stem-mounted sensors, these units will be located very close to the wheel, so again, be careful. For tire demounting, some OE service manuals advise first deflating the tire, then removing the sensor’s retaining nut (clamp-on style) and dropping the sensor inside the tire. This keeps the sensor out of harm’s way during bead breaking and demounting.
If the sensor is visible (when replacing a sensor, when a sensor is already in place and a tire is about to be mounted, etc.), be sure to note the ID number on the sensor. This number will be required for input when initiating or resetting. Remember to write the number on a piece of paper before mounting the tire.
Pay strict attention to torque specifications with regard to installing either a clamp-on or snap-in type sensor. Overtightening can damage the sensor and/or the valve core.
Some TPMS share the keyless entry’s receiver. This means that the remote key fob may be needed for specific procedures. Be careful to avoid “playing” with the key fob remote during any TPMS procedures.
Don’t replace wheel sensor parts haphazardly. Some sensors feature aluminum caps and nickel-plated cores. The end of the valve stem may serve as the sensor’s antenna. Only replace cores or caps with the correct originals.
Use only a high quality pressure gauge when filling or checking tire pressure on any TPMS. The sensors found on direct systems are very sensitive and precise. Using a dime-store gauge (or a mis-calibrated air gauge at a service station or car wash location) can lead to slightly over- or under-inflating the tire, which may be enough to cause a system warning light to activate.
Quality pressure gauges have always been necessary, but the use of TPMS creates an even greater need for accurate readings.
Common TPMS sensor problems
Here we present a variety of TPMS service tips provided courtesy of select manufacturers.
The following are tips provided by John Rice at 31 Inc.:
Select the right make, model and model year. It used to be that you could tell the model year of a vehicle from its build date. A fall build date meant a new model. Those days are over. Manufacturers now introduce new models throughout the year. Mid-model year changes cause some of the biggest TPMS headaches. The Vehicle Identification Number (VIN) is the most accurate way to determine the model year of a vehicle. The tenth digit of the VIN corresponds to a specific model year. For example, a tenth digit J indicates the vehicle is a 2018, K a 2019, and so on. The Smart Sensor Elite Tool has a VIN scanner that allows you to accurately scan the barcode on the B pillar to determine the correct make, model and model year of the vehicle you are servicing.
Check the light on the dashboard. It is important to properly diagnose TPMS issues. Technicians should check, and note, the light on the dashboard whenever servicing a vehicle. Note the status of the TPMS light immediately after starting the vehicle. A solid light indicates one, or more, of the tires is significantly underinflated. A blinking light, or the letters TPMS, indicates a system malfunction (most likely something to do with a sensor or relearn). Blinking lights go solid after 60-90 seconds.
Test before you touch. After checking the light on the dashboard, checking the sensors is next on the list. Before performing any tire/wheel service, technicians should check the TPMS sensors. This is done by simply scanning the sensors using your TPMS tool. Here’s where you can identify which sensor(s) is working properly, and which one(s) requires service or replacement. This is where you will also confirm all sensor IDs are unique. Duplicate sensor IDs can also cause a system malfunction (blinking light) and more headaches. Also, always do another quick scan of each sensor after programming a programmable sensor — and do it before doing a relearn to make sure all sensors are programmed properly and there are no duplicate IDs.
Confirm direct or indirect TPMS. Direct style TPMS uses sensors in the wheels/tires. This makes up roughly 90% of all TPMS. Indirect TPMS does not use sensors mounted in the wheels/tires. Instead, indirect systems work through the vehicle’s ABS. Indirect systems are used by Audi, Honda, Mazda, VW and others. Even though they represent a small percentage of total vehicles, with TPMS, it is important to identify these vehicles early on during your initial inspection so you are not pulling your hair out later trying to figure out why the sensors are not responding on a 2018 Volkswagen Passat. The Smart Sensor Elite Tool, for example, lists the indirect vehicles to take the guesswork out of servicing and identifying them.
Scan the programmable sensor before installation. Universal/programmable sensors, like the Smart Sensor One, have made TPMS replacement simple and easy for the shop. One SKU can service 99% of all direct TPMS-equipped vehicles. These sensors are like a “blank sheet of paper” and can be programmed for virtually any vehicle application, but they need to be programmed out of the box. Before installing the sensor, technicians should scan the sensor, as a check, to make sure the sensor was programmed properly and there are no duplicate IDs. Each sensor must have a unique ID (like a Social Security number). This step can save technicians a lot of hassle down the road.
Ford has two relearns. This causes a lot of confusion and headaches for technicians. One is for tire rotations, which uses the hazard switch to initiate the relearn (this procedure is typically listed in the owner’s manual). The other is used when a new sensor has been introduced on a vehicle, and uses a sequence of steps to put the vehicle into learn mode by cycling the ignition switch (this procedure is not listed in the owner’s manual). See the potential for confusion?
Bartec USA offers these tips of what to look for during a TPMS service:
TPMS sensors with aluminum valve stems can corrode over time. Depending on the climate, it can occur very quickly. If the sensor wasn’t properly serviced, or the wrong service kit was used, or the incorrect valve core inserted, the breakdown and corrosion can happen fast. The key to long life for a TPMS sensor is to make sure it gets proper service each time the tire is removed from the wheel. Replace the wear items, seals and valves to help prevent premature damage from corrosion.
Being that we are in our 15th model year of full TPMS fitments, and the average age of a vehicle on the road is at an all-time high, the frequency at which TPMS sensor batteries are dying is on the rise. The issue is knowing it! Test-before-touch — a pre-inspection with a TPMS tool — is the best way to find out if a sensor is not functioning. The TPMS MIL [flashing light] might not always be present, so testing with a tool is the best way. Using a tool to inspect all the sensors prior to work beginning is the key to preventing a missed faulty sensor.
Vehicles are also showing up in service bays with no sensors at all! This presents a unique challenge as it is very likely that the TPMS light is flashing and because the sensors are missing, the system is not operative. As a vehicle service provider your job is convincing the consumer of the critical importance of returning the TPMS to the operational state. Proper installation of replacement sensors and recalibrating the system does just that.
Wrong sensor installed
Like a missing sensor, if the wrong replacement was used, or the replacement wasn’t properly configured, the TPMS MIL might be flashing. A TPMS diagnostic tool is required to determine what fault codes are present and what kind of sensor is fitted to the wheel.
Choosing a replacement sensor
Someone once said the solution can sometimes be worse than the problem. Selecting a TPMS replacement sensor used to be that way! Replacements fall into one of three categories: Direct replacement, multi-protocol and programmable. These categories are based on how the sensors are fit for use and how they operate, and whether TPMS tools are required to use them.
Direct replacement TPMS sensors are typically a “part for part” fitment. One part number cross references to the OE fitted part number. These sensors can be purchased in the form of OE equivalent, factory direct or in aftermarket versions. Whenever a new OE part number is created, an update is required in the direct fit replacement fitment guide. This type of sensor, like the OE sensor, requires a TPMS tool only to complete the TPMS relearn, and not to configure, prep or program the sensor.
Multi-protocol TPMS sensors are direct replacements for the original parts, except that one sensor contains “many protocols.” As the name suggests, one sensor has been created to “house” multiple sensor output protocols which means that fewer part numbers cover a wide range of OE part numbers. The way these sensors work is, with each transmission, a number of different protocols are sent out. When fitted on the proper vehicle, the correct data is received and processed. Today’s multi-protocol sensors often require a TPMS tool to prepare for use.
Finally, there are programmable replacement sensors. Programmable sensors offer the greatest flexibility, ease of use and help keep inventory costs low. These sensors require programming before installation. Programmable sensors offer the greatest flexibility while keeping the SKU count to a minimum.
NOTE: The advantage to programmable sensors is that as new protocols emerge [coverage], the sensor can be updated with the new coverage. This limits new SKUs and obsolete stock. Bartec has developed a unique and exclusive process called Rite-Sync. Rite-Sync combines sensor programming with the vehicle relearn into a single, easy, and fast process. The tool guides the entire process and cuts the typical service time in half, while eliminating common mistakes.
Autel provided these TPMS tips:
TPMS sensors can stop functioning for many reasons including battery failure. Original TPMS sensors have a battery life of about seven years. Deterioration can be caused by weather conditions, the valve stem being snapped either in a road or parking mishap, or it can be damaged during tire removal.
Other issues causing system errors include a mismatch between the sensor IDs registered within the module for the particular wheel location and the actual ID on the sensor installed on the wheel. The reason for this is the sensor IDs have not been correctly “relearned” to the vehicle. This can happen if a new sensor is installed and not relearned, or if the tires have been rotated and the IDs have not been relearned so the actual sensor locations don’t match what is registered.
The at-a-glance status screen on Autel's TPMS tools eliminates the guessing game by identifying the error, whether it's a broken sensor, relearn issue, or if there is something amiss with the module.
Here are seven things to avoid when completing TPMS service, offered by Continental:
Using a scan tool with out-of-date software. Keeping the TPMS scan tool up to date is one of the most important service steps technicians should take because most of the service issues they will encounter can be caused by out-of-date tool software. The ability to diagnose TPMS faults and relearn sensors to the vehicle are the two most notable problems technicians encounter when the scan tool is not up to date. TPMS relearn tool manufacturers update software almost on a monthly basis. Many factors can initiate a software change, such as new vehicle model introductions or older vehicle recalls. Keeping the relearn tool up to date with the latest software will ensure quick and accurate relearns.
Failure to perform the factory relearn. Factory relearn procedures should be performed every time a tire or TPMS sensor is serviced to ensure that the entire TPMS system is fully functional. Because the sensors work in harmony with the vehicle’s receiver, skipping this step can send incorrect information to the vehicle operator and create a safety concern.
Improper vehicle application verification. In order to determine and install the correct replacement TPMS sensor, it is essential to have the exact vehicle year, make and model data. Quite often the vehicle model year is not the same as the vehicle build date. There are a couple of easy ways to identify the correct vehicle data quickly and accurately. One way is to confirm the production year by using the 10th digit of the VIN. Another is to use a relearn tool with a VIN reader feature. Either way, knowing exactly what vehicle is being serviced will help the technician to identify the correct replacement TPMS sensor.
Not replacing the service parts. When a tire service is performed, a service kit should be used to replace the TPMS sensor mounting seals, hex nut and related hardware. This is highly recommended and important. These components are key to providing a leak free seal between the TPMS sensor and the wheel. Technicians should never reuse the old service parts.
TPMS battery confusion. Most TPMS sensors run on batteries that are built into the sensor and not replaceable. Battery life expectancy can range from eight to 10 years, depending on vehicle use, driving habits and environmental conditions. If a TPMS sensor fails because of a dead or weak battery, some technicians will replace the individual sensor. However, as a best practice, technicians should consider replacing the other sensors since it’s likely they are close to failing as well.
Not performing a relearn after a tire rotation. If the tire location on a vehicle is changed, the technician should perform the TPMS relearn procedure. Many vehicles offer a “pressure by location” feature that shows drivers which tire is not at the factory recommended pressure. If the tires are rotated and a relearn is not performed, the TPMS sensors could transmit an incorrect location to the driver.
Not using a torque wrench to install a TPMS sensor. Technicians should always use a torque wrench tool to tighten TPMS sensor hex nuts and other threaded TPMS components to proper specifications. Proper torque on the nut at the base of the valve stem is critical to the TPMS sensor assembly. Excessive torque can damage the sensor and insufficient torque can allow air leaks to develop.
Yanik Leduc, global technical training manager at Schrader, offered this advice:
The most common question we receive from technicians calling our technical support hotline is: “I’ve just ordered a new sensor, but I can’t make it work with my tool.” This call represents almost 25% of all daily calls.
I was recently presenting at ATE (Automotive Training Expo), and a participant asked, “If the main benefit of a programmable sensor is to decrease the number of SKUs I need to keep in stock, can you explain to me why I need two or three different TPMS tools in my shop?”
His concern is totally understandable. To choose the appropriate sensor, technicians not only need to consider vehicle coverage, but also things like sensor fitment, sensor capacity to replicate OE specifications, sensor type, and finally, sensor and tool compatibility.
Programmable vs. OE replacement TPMS sensors
The main benefit of a programmable TPMS sensor is, without a doubt, the fact that it can cover 85% to 99% of vehicles in operation (depending on the brand) and require keeping in stock only one or two part numbers. It is significant inventory savings compared to an OE replacement sensor from which a shop would need to keep in stock more than 90 different part numbers to cover 85% of vehicles in operations. On the other hand, OE replacement TPMS sensors will replicate the OE sensors in their form, fit and function and the sensors are ready to use straight out of the box. Programmable sensors, as the name says, need to be programmed with a compatible TPMS tool to work with a given make, model and year.
Tool and sensor combination
To get the most bang for your buck, many shop owners will choose a programmable sensor and a compatible TPMS programming tool that offers the most vehicle coverage. The good news is that most TPMS companies will offer tool and sensor bundles that allow shops to equip themselves with a brand new TPMS tool and a few sensors at a very good price.
Your shop is now equipped with sensors and tools to service 99% of vehicles in operation. But what about the 1% that remains? What will happen when you need to service a vehicle that is not covered by your tool and sensor combination? Can you program other brands of sensors with that tool you’ve just purchased?
Most tool and sensor bundles available today come with a TPMS programming tool locked to program a specific brand of sensor. Still, many shop owners feel trapped as they can’t program other brands of sensors when they need to and end up buying a second or third bundle with different coverage and a different tool still locked to a different sensor brand.
If you need to service a vehicle that is not covered by your tool and sensor combo, you don’t necessarily need to buy another tool and sensor bundle. Your tool might be locked to one brand of sensor, but it’s only locked to program it. You can still read any sensor on any vehicle. This means that you can order an OE replacement sensor that doesn’t require programming. This allows you to fully service the TPMS of a vehicle even if it’s not covered for programming by the sensor brand. Also keep in mind that some bundles are available with tools that are unlocked to program multiple brands of sensors, such as the Schrader S57 or S56 tools. You just might need to shop a little more thoroughly.
Finally, whenever you’re looking to invest in new TPMS equipment, my recommendation is to not only look for a sensor with great vehicle coverage but to look for a TPMS partner. Search for a supplier that can provide you with programmable sensors with great coverage, as well as a wide variety of OE replacement sensors, technical support and top-notch training.
Ryan Dalton of Hamaton says these are the most common issues technicians face.
Keep TPMS tools updated. Having a valid software subscription and keeping TPMS tools is essential. Software updates provide new features and increased coverage.
Put Ford vehicles into relearn mode. For Ford vehicles with standard ignitions, press and release the brake pedal while the vehicle is off. Then turn the ignition from off to run three times, stopping in the run position. Then press and release the brake pedal once more, then repeat the second step. Please note that all steps must be completed within 10 seconds.
Copy IDs if the OE sensor is dead: With a compatible TPMS tool, technicians can retrieve IDs from the ECU (via an OGDII module) or manually enter the OE sensor ID — it’s often found on the sensor housing.
Reset the TPMS light: The correct time to reset the TPMS light is once the tires are properly inflated or after a successful OBDII relearn. Turn the ignition to on, but do not start the engine. Hold the TPMS reset button until the light blinks three times. Then start the engine and wait 20 minutes for the sensors to refresh.