TPMS tips:Identifying types, applications, functions and service
Every vehicle from 2008 model year to the present is equipped with a tire pressure monitoring system (TPMS). If you service tires, you’ll be forced to deal with TPMS. That means that you must invest in a TPMS tool (preferably a combination tool that allows scanning/diagnostics, activating, programming if needed and relearning).
However, it doesn’t stop there. In addition, you must also have the appropriate mechanical tools that are dedicated specifically to TPMS (calibrated torque wrench for hex nuts, calibrated torque wrench for stem installation and for core installation), and rubber grommet install and remove tools; as well as an assortment of service kits (stems, hex nuts, caps, cores, grommets and seals).
There’s no way around this. Either you’re in the TPMS business or you’re not (and if you sell and/or service tires, you are in the TPMS business).
Pay attention to materials
If you’re dealing with aluminum TPMS valve stems, pay attention to the valve cores and caps. Aluminum stems and cores are nickel plated to avoid galvanic corrosion issues. Don’t just toss any core into an aluminum TPMS stem. The same goes for caps — to avoid corrosion issues, you cannot thread-on just any valve cap that’s lying around the shop onto a tire pressure sensor. Don’t use a metal cap, as this can corrode and in most cases not be removable from the aluminum stem. Some aftermarket caps in particular may be made entirely of steel or stainless steel, or they may have a dissimilar metal (female thread) insert encased in plastic.
Galvanic corrosion can occur when dissimilar metals join, so threading a dissimilar metal cap or metal-insert cap onto the sensor’s stem can result in the cap binding to the stem, making it difficult to remove in the future. If this happens, force may be required to remove the cap that can result in breaking the sensor’s valve stem. This problem is becoming more apparent as the number of vehicles equipped with TPMS increases, and as more owners tend to “enhance” the wheels’ appearance by getting rid of “the ugly plastic caps” and installing chrome-like caps, or when an unwitting DIYer or technician previously installed a non-TPMS cap. If the cap is made of metal and you’re not sure of the base material, don’t use it.
According to Tyson Boyer at Dill Air Controls Products, this is a major concern, but also presents the service provider with an opportunity to educate the customer.
“If you don’t include TPMS in your inspection process and empower your team to properly inspect every vehicle, you are significantly increasing your risk of presenting the unwanted result versus sharing the findings. Corrosion has created technician resistance toward servicing aluminum valve stems. To aid in stronger acceptance and to do what’s right for the customer and your business, we have developed a corrosion-free valve stem. By using an electrolytic process, we were able to chrome-plate a brass cap/stem, which will be available for use with the REDI-Sensor this summer.”
As noted by the TPMS division of JohnDow Industries, there are many different OEM sensors on the market today but there are only two styles of sensors.
- One-piece: A one-piece sensor has the housing and valve molded together. The valve is not removable. The items that should be serviced on this style of sensor are: valve core, hex nut, grommet, cap and washer. If the valve is broken or corrosion has occurred, this sensor is not serviceable and the entire sensor will need to be replaced.
- Two-piece: A two-piece sensor has a removable valve stem that can be separated from the sensor housing. Here is a list of what can be serviced on this style of sensor: replacement valve, valve core, hex nut, grommet and cap. With this type we also have two different valve configurations:
- Snap-in rubber valve, valve core and cap. The OE manufactures recommend replacing the rubber snap-in TPMS valve whenever the sensor is removed from the wheel. The rubber snap-in valve is attached to the sensor module by a hex nut (or Torx screw).
- Clamp-in metal valve, valve core, hex nut, grommet and plastic cap. Whenever aluminum TPMS sensors are removed from a wheel, the sensor should be fitted with a new rubber grommet, aluminum retaining nut, special nickel-plated valve core and valve cap. It is important that all components be torqued to appropriate values to prevent air leaks. Attempting to reuse the original rubber grommet, valve core and retaining nut may result in an air leak.
Test before touching and don’t skip the re-learn
Scot Holloway of Bartec USA Ltd. reminds us of an important tip when servicing any TPM system. He recommends completing a “test before you touch” inspection. Being aware of the system’s condition is critical before you begin servicing the system. Use a TPMS activation tool to check for fault codes and to test the sensors. Instead of blindly installing an original sensor when performing a wheel change, or when installing a new stem to the sensor during a tire change, testing the health of the system will alert you to any problems that must be addressed, to avoid repeating your sensor mounting and tire mounting/balancing chores.
While cloning a sensor and expecting the system to re-learn on its own may work, performing a re-learn helps to verify that the system will function as designed, without the TPMS MIL activating once the vehicle leaves the shop. A re-learn simply involves programming the vehicle’s control module. The three types of re-learn include stationary, OBD and automatic.
Stationary reprogramming is possible in about 25% of applications. This is performed with the vehicle parked and placing the system into its learn mode (depending on the vehicle this may involve a number of key fob on/off steps). A TPMS activation tool is then used to force the sensors to transmit (the horn may sound indicating a successful sensor reprogramming).
OBD re-learn, applicable to about 36% of applications, requires a combination-type TPMS tool, enabling you to retrieve sensor data and connect to an OBD port in order to program the sensors to the module. According to Bartec, new IDs can be programmed without driving the vehicle.
Auto learn applies to about 39% of vehicles and involves driving the vehicle following sensor service, where the new sensor IDs are “learned” and programmed automatically to the control module. This also turns off the TPMS light. No tool is needed.
Performing a relearn using a combination tool allows you to clear any stored TPMS fault codes. If any codes are not cleared, the TPMS MIL may begin flashing once the customer leaves the shop.
Direct replacement sensors
These sensors are direct replacements for sensors that were originally installed by the automaker. Direct replacement sensors are typically a “part for part” fitment. One part number cross references for the OE part. They are available from both OE dealers and aftermarket sources.
These sensors are direct replacements, except that fewer part numbers cover a wide range of OE part numbers. These sensors contain multiple protocols for a range of vehicles. The ECU will filter out the one that applies to the specific vehicle at hand.
This type of sensor requires programming prior to installation. Fewer part numbers cover a wider range of applications. Fully programmable sensors are fully programmable for protocol and ID, using a low frequency signal from a programming tool. ID-programmable sensors feature only ID programming. Typically there are more part numbers listed by OE protocol. A programming tool is needed to program or copy the sensor ID. Contact programmable sensors are fully programmable (ID and protocol) using a programming tool’s contact pins.
Multi-application sensors eliminate the need to clone or to load vehicle software protocols, requiring only the OEM relearn procedure using a TPMS scan tool.
Examples of pre-programmed sensors that already meet specific OE protocols are 31 Inc.’s Multipro sensors, VDO REDI-Sensors and John Dow DVT sensors. These can be triggered, read and relearned with all major TPMS scan tools. Examples of OEM direct replacement sensors are offered by Huf (tpmsdirect.com). Examples of programmable sensors that allow you to copy the ID of OE sensors are Group 31 Inc.’s Smart Sensor Pro sensors, Standard Motor Products Inc.’s clone-able sensors, and Schrader International Inc.’s EZ-Sensors.
Another example of sensor design is Schrader’s WAL technology (Wireless Auto Locate). This breed of sensor allows automatic location of each sensor’s individual pressure, an advantage when rotating wheel/tire assemblies.
The proliferation of aftermarket sensor designs continues to grow. You simply need to decide what type of sensor to use (direct replacement, programmable or multi-protocol). Universal and programmable sensors are popular today, simply because they reduce inventory needs and are so very flexible in terms of application.
As John Rice of Group 31 reminds us, TPMS sensors come in two flavors, frequency-wise (megahertz): 315 MHz and 433 MHz. Whenever you grab a universal/programmable sensor, make sure that it has the correct electromagnetic wave frequency for the vehicle system. Your TPMS scan tool will recognize the frequency of either the old or new sensor.
Make sure that you match the frequency! Don’t assume that all models and model years from the same automaker use the same frequency. For example, a 2010 Dodge 2500 may use 315 MHz while a 2010 Dodge 1500 may use 433 MHz. Remember to verify the frequency of the replacement sensor.
With the up-to-date TPMS tools available today, cloning a TPMS sensor is an easy task. When replacing an original sensor with a new clone-able sensor, locate the ID number on the old sensor. Place the new clone-able sensor into the holding tray of the tool. Enter the old sensor’s ID number and press enter. Write the cloned ID on the sticker provided with the new sensor and affix the sticker onto the new sensor. Then perform the OEM relearn.
When to clone
Before servicing a vehicle with a TPMS issue, Standard recommends a “Test, don’t guess” diagnostic strategy. Performing a simple bulb check to confirm if a TPMS light is on solid or flashing is a great first step when diagnosing a TPMS issue.
A solid TPMS indicator lamp indicates a low-pressure condition. A TPMS indicator lamp that flashes for the first 60 to 90 seconds with the key in the “Run” position indicates a system fault, possibly caused by an inoperative sensor.
In addition to the TPMS indicator lamp, many vehicles can utilize the Driver Information Center to display both tire pressure by position and a written message indicating TPMS service is required.
If the TPMS lamp is on solid, the first course of action is to reference the tire placard located on the inside of the driver’s side door jamb and ensure all tires, including the spare, are inflated to the proper pressure. If the TPMS indicator lamp remains on after properly inflating all tires, it may indicate a TPMS issue that requires further diagnosis. If the TPMS indicator lamp is on and flashing, there is a need to investigate and determine the root cause of the fault. In this case a TPMS tool is required to activate and read each TPMS sensor to determine if they are functioning properly.
There are several reasons a TPMS light may be flashing:
- The TPMS system was not reset following a tire rotation.
- A faulty TPMS sensor is not transmitting properly due to a dead or weak battery.
- The TPMS receiver on the vehicle is faulty and cannot pick up the signal being transmitted by the individual TPMS sensors.
- The RF antenna or wiring connecting the antenna(s) to the TPMS receiver is faulty.
- A sensor was removed and not replaced in one or all of the wheels.
For the numerous faults that can cause the TPMS light to turn on, Standard offers some unique solutions to complex TPMS issues. Industry-leading cloning capabilities in both OE matching and QWIK-SENSOR multi-coverage, programmable TPMS sensors can save time and money in the bay.
Cloning a TPMS sensor is the process of copying an existing sensor ID number and, in many cases, sensor protocol (as with programmable sensors) to an aftermarket clone-able sensor by using a sensor cloning/programming tool. The copied sensor is intended to appear to the vehicle’s TPMS module as the previously installed/old sensor.
You can use cloning technology to your advantage to save time and money in the bay when:
- A sensor or sensors are no longer transmitting a signal due to a weak or dead battery.
- A corroded or faulty valve stem cannot be replaced separately and requires you to replace the sensor and valve stem as one unit.
- A desire to have a second set of tires and wheels that can be installed anytime with no factory relearn.
- You are using a tool that can trigger, program and clone a sensor but has no OBD-II capabilities to perform a factory relearn (some vehicles such as Toyota require an OBD-II tool to do the relearn).
- Your tool is not capable of communicating with the vehicle’s TPMS module, but you can read the existing sensor and clone the replacement QWIK-SENSOR or OE-matching sensor.
It is always recommended to perform a relearn with each TPMS service. In instances when it can’t be performed (tooling issues, driving conditions, etc.), cloning will get you out of a jam and save you time. To put our tips to practice, you can find the software required to clone or program standard OE match and QWIK-SENSOR multi-coverage programmable sensors on all major TPMS tool brands, including ATEQ, Bartec, Snap-on Inc. and OTC (Bosch Automotive Service Solutions LLC).
In all TPMS systems, the order in which the control module recognizes wheel positions is the same: left front, right front, right rear and left rear.
Whenever performing a relearn, follow this order. Also, using a quality TPMS scan tool, you can determine if the order has changed even before you begin to work on the vehicle. For example, let’s say that the TPMS warning light is flashing (remember: a steady light indicates a low pressure condition, while a flashing light indicates a system problem). When scanning the system, you may be told that the right rear sensor location is the problem.
However, someone may have rotated the wheels previously and did not perform the relearn. Even though the module tells you that the problem is the right rear, the left front might be the real problem, because the left front and right rear wheels were swapped without a relearn procedure. Using a quality combination TPMS tool, you can determine that the order has changed and can address the real source of the problem, followed by a relearn in the proper wheel position order. The system will always recognize the first programmed sensor as the left front. The second sensor to be programmed will be recognized as the right front, etc.
The order is always LF/RF/RR/LR.
Where are the TPMS sensors?
While we’re accustomed to assume that all 2008 and later vehicles in the U.S. feature TPMS that incorporate individual pressure sensors in each wheel, be aware that newly introduced and refined indirect TPMS systems are creeping into the country, citing some VW, Audi and now Honda models.
These systems do not feature “traditional” TPMS sensors in the wheels, but rather use an evolved ABS to determine tire pressures (obviously based on tire diameter as an aspect of inflation pressure).
As Group 31 Inc.’s TPMS expert John Rice points out, if you walk around a vehicle with your TPMS scan tool and don’t find a TPMS sensor signal at all four wheels, that’s a pretty good indication that the vehicle may be equipped with one of the indirect systems.
Factory relearn procedures
Not all automaker relearn procedures are identical, even within the same vehicle brand. GM, for example, has some 20 different relearn procedures for various models and model years. If one specific GM relearn requires you to turn the key on and off 12 times, run three laps around the car and wait for the horn to beep four times (just kidding, but barely), don’t assume that this same procedure applies to all models. If in doubt, refer to the service manual or owner’s manual. A good TPMS scan tool may provide the proper procedure in its relearn mode.
When to install a service kit
Whenever you access the sensor (as in whenever a tire is removed), always install a new service kit (in the case of aluminum stems, always replace the grommet, seal, core, hex nut and cap). Rubber materials age and wear. Even if the rubber, hex nut and core appear in good shape, do not assume.
TPMS is considered a safety system, and before the vehicle leaves your shop, you need to do all you can to make sure that this system is operative and in good condition.
Just as you would always replace a rubber valve stem whenever installing a new tire, you need to replace these critical hardware items. When dealing with a sensor that features a snap-in rubber stem, replace the stem and core.
Example of installing an EZ-Sensor
(This is merely one example, citing a specific vehicle and specific sensor):
Sample vehicle: 2011 Toyota Corolla.
- Using a scan tool, test each sensor to determine if a fault is present. If a fault is present in the RF, for example, remove the wheel/tire assembly from the vehicle.
- Remove the valve core and discard.
- Remove the hex nut that secures the sensor to the wheel, and allow the sensor to drop into the wheel well.
- Break the tire bead with the wheel positioned with the valve hole at 12-o’clock, then 6 o’clock (repeat for the opposite side bead).
- Remove wheel weights.
- On the tire changer, position the change duck head in line with the valve hole and demount the tire.
- Using the TPMS tool and an EZ-Sensor, “create” a “RF” sensor (allowing the tool to program and recognize the sensor as position right front).
- Install the sensor to the wheel (the EZ-Sensor features a snap-in rubber stem).
- Mount the tire, with the valve placed just ahead of the traction point (where the bead first makes contact with the rim — 180 degrees from the change head).
- Release the wheel from the changer claws and inflate the tire.
- Install a new TPMS valve core, torque the core to specification and inflate the tire to specification and install a new TPMS cap.
- Install the wheel assembly to the vehicle, torquing wheel fasteners to spec.
- Perform a relearn procedure following the proper wheel location order (LF/RF/RR/LR).
- After all four IDs are set, connect the scan tool’s cable to the OBD port on the vehicle. With the ignition on, write the IDs to the vehicle. The TPMS light on the dash will flash until the process is completed.
Aftermarket system retrofit
The monitoring of tire pressure isn’t limited to only vehicles that were equipped with TPMS from the factory (starting in 2007). Older vehicles may be easily retrofitted with a complete TPMS.
Dill, for example, offers a complete system (including sensors and monitor/receiver) for both two- to 10-wheel vehicle applications.
Torque is critical
When performing assembly of a sensor (installing a new stem to the sensor in cases where the stem is secured to the sensor with a screw), or when installing the sensor to the wheel (tightening the hex nut in applications that feature an aluminum stem fitted with a hex nut), tightening the value is absolutely critical, both to obtain proper grommet sealing and to prevent over-tightening which can easily damage the sensor or stem.
Typical torque values for TPMS sensor assemblies range from 12 to about 106 inch pounds. The 12 in.-lbs. range typically applies to the screw that secures the stem to the sensor, in designs that feature this type of attachment. This range is not usually available with a conventional inch-pound torque wrench. A dedicated torque wrench that is specifically designed for TPMS service is absolutely essential. Various styles are currently available that include electronic (and adjustable) torque wrenches to pre-set-value torque wrenches that feature a “breakaway” feature when the torque value is reached. These tools are available from just about any manufacturer that offers TPMS sensors and/or sensor service kits.
Do not guess at sensor screw or nut tightening values by “tightening by feel.” Under-tightening can lead to pressure loss and potential loosening of the sensor. Over-tightening can easily damage the assembly and/or cause a pressure leak. As an example of how critical torque values are, the tightening value of the screw that secures the valve stem to the sensor can impact the signal transmission of the sensor to the receiver and module. If under- or over-tightened, the radio signal may be compromised, which could easily lead you to think that the sensor itself is at fault. ●