Tire pressure monitoring systems
We've discussed the subject of TPMS (tire pressure monitoring systems) in the past, but this is a topic that can always benefit from an update. Considering the proliferation of TPMS in today’s market, it’s vital that we gain as much understanding of these systems as possible.
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 have lost 25% of the recommended cold inflation pressure (placard pressure). A direct style tire pressure monitoring system (most widely in use today) features a pressure sensor/transmitter installed inside each wheel. The sensor constantly reads inflation pressure. The sensor then sends a radio wave signal to a receiver located in the vehicle. When inflation pressure falls below a predetermined level, a warning light illuminates on the instrument cluster. Depending on the year, make and model of vehicle, this warning may simply indicate a low-pressure warning, leaving it up to the owner or technician to then determine which tire location is underinflated; or the warning system may indicate which location (LF, RF, LR, RR) is underinflated.
Instead of monitoring actual inflation pressure, an indirect system relies on the vehicle’s wheel speed sensors for the ABS to monitor tire rotational speed (since a lower-pressure tire will rotate at a different speed due to the decrease in overall tire diameter). When the ABS detects a different rotational speed, it alerts the driver. This works as designed as long as the system detects a difference in rotational speed as compared to the remaining tires. However, one challenge is if all four tires are underinflated by the same amount, the system may not detect a difference, and no alert warning may be provided. A direct TPMS is much faster and more accurate by comparison.
Indirect systems can also cause false tire pressure warnings if/when tires spin on slippery surfaces. If this happens often enough, the driver may be accustomed to ignoring the warnings and may ignore actual low-pressure alerts.
Three basic “styles” of TPM sensor/transmitters are available (note: the correct OEM term for the sensor is “wheel mounted sensor”): banded, snap-in and clamp-in. Banded sensors are affixed to the inside of the wheel using both a positioning adhesive (peel off) and a large diameter worm-drive clamp (the wheel valve is the standard valve style that has been in use for decades). Both clamp-in and snap-in sensors feature the valve stem as an integral part of the sensor. A clamp-on sensor mounts via the wheel’s valve hole and is secured with a mounting nut and is sealed with a separate grommet. The snap-in style features a traditionally-mounted rubber valve style that allows the valve stem to be pulled through the hole and “snapped” into place similar to a traditional valve.
NOTE: When servicing any TPMS sensor, do not use a brass valve core. This can result in dissimilar metal reaction and can lead to corrosion issues. Use only the valve cores provided with specific TPMS service kits, which are special nickel plated brass. Whenever a valve core has been removed, always replace it with a new core. Also, only install a valve cap that is designed for use with TPMS. This should a plastic cap and will feature an internal O-ring for better sealing. The use of a steel or brass cap can also lead to dissimilar metal reaction.
RELEARN VS PROGRAMMING
Vehicle relearn and sensor programming are completely different procedures. Confusion is common due to the availability of aftermarket TPMS sensors that are offered as “programmable,” “universal” or “cloneable” sensor units. These sensors must be programmed with the proper protocol/software application information for the vehicle before they can be installed on the wheel. An exception is VDO’s REDI-Sensor which does not require sensor programming prior to installation (these sensors are already loaded with protocols needed to function with the vehicle’s system).
Regardless of the brand of sensor, once programmed and installed, the sensors must then be relearned to the vehicle, even if only one sensor has been replaced. It’s not uncommon for shops to overlook the necessary vehicle relearn step, proceeding under the assumption that the sensor programming was all that was required. This misunderstanding can result in comebacks and customer complaints.
Vehicle relearn is a standard and mandatory procedure whenever a sensor has been replaced, and that includes both OE or aftermarket sensors, in order to ensure that the TPM system functions properly. Some vehicles such as specific models from Chrysler and Mazda automatically learn replacement sensors during an initial drive cycle. Other than these exceptions, a TPMS scan tool is required.
NOTE: Since relearn procedures vary among automaker brands, it’s necessary to determine the correct procedure for any given vehicle before starting the relearn process.
CONDITIONS WHEREIN THE SYSTEM MAY NOT FUNCTION PROPERLY
1. Similar radio frequencies in the immediate area may interfere with the system.
2. A radio device of similar frequency is being used in the vehicle.
3. The tire pressure warning valve sub-assembly’s sensor battery may be depleted.
4. Wheels may be installed on the vehicle which do not feature a tire pressure monitor valve sub-assembly.
5. Use of studded snow tires or tire chains may disrupt radio signals.
6. If non-specified wheels are used, the system may not function properly because the radio waves are disrupted.
7. Depending on the type of tire used, the system may not function properly even if the correct specified wheels are used.
NOTE: The tire should be completely removed from the wheel before installing any new sensor. When dealing with a sensor that is secured to the wheel with a mounting nut, BE SURE to tighten at the specified torque value. Over-tightening can easily damage the stem.
When mounting the tire onto the wheel, install the inner tire bead first. Position the main body of the valve sensor approximately in the 7 o’clock position relative to the mounting machine’s bead pusher arm. If the valve sensor is positioned outside this area, it may create interference with the tire bead with resulting sensor damage.
Install the upper bead, being careful not to damage the valve sensor (make sure that the valve sensor is not clamped by the bead).
After the tire beads have been seated and the tire has been fully inflated, re-check the valve nut and retighten to the vehicle manufacturer’s specification (some sensors are as low as 35 in-lbs, whereas others require up to 80 in-lbs. Valve stem damage can easily result from overtightening, so ALWAYS refer to the proper torque specifications for your application! Check for air leaks with a soapy water solution.
TPMS VEHICLE RELEARN EXAMPLES
Following are a few examples of the steps required for TPMS vehicle relearn. If the replacement sensor(s) require programming, sensor programming must be performed prior to the vehicle relearn procedure. The following examples were provided courtesy of VDO. The TPMS vehicle relearn for your specific vehicle must be checked via application cataloging-examples only.
FORD WITH PUSH-BUTTON IGNITION
Ford vehicles that are equipped with a push-button ignition switch require a specific sensor relearn procedure. Once the replacement sensor(s) has been installed and all four wheels/tires are mounted to the vehicle, inflate all tires to the placard pressure and follow these steps:
1. Ignition OFF. Be sure that the vehicle is in Park or Neutral and properly secured.
2. Press and release the brake pedal once.
3. Cycle the ignition button from OFF to RUN three times, ending in the RUN position (this is the same procedure that would be used if the vehicle is key-ignition equipped).
4. Press and release the brake pedal again, and press the ignition button to the OFF position.
5. Cycle the ignition button from OFF to RUN three times, again ending in the RUN position. When the vehicle horn honks, this indicates that the relearn procedure has been initiated. You are now ready to begin learning the sensors to the vehicle.
6. Using a TPMS scan tool, trigger each sensor, starting with the LF wheel and working clockwise (LF, RF, RR, LR). If the vehicle is equipped with a sensor in the spare tire, be sure to trigger that wheel’s sensor as well (typically after triggering the LR, follow the prompts). The TPMS scan tool is held at the tire sidewall closest to the valve/sensor during triggering.
Once the relearn process is complete, the vehicle horn will honk to confirm.
CHRYSLER, MAZDA AND SOME EUROPEAN VEHICLES
This procedure applies to TPM systems that are otherwise auto-relearned once the vehicle is driven. If driving the vehicle is impractical at the time, a TPMS scan tool may be used to perform the relearn in the shop.
With wheels/tires installed to the vehicle and inflation pressure adjusted to specification, trigger all sensors using an OBD II-compatible TPMS scan tool, starting with the LF and working clockwise (LF, RF, RR, LR). If the vehicle is equipped with a sensor in the spare tire, be sure to trigger that wheel’s sensor as well (typically after triggering the LR). Trigger the spare (if so equipped) last.
Once all sensors have been triggered, place the ignition switch to the ACC or ON position (do not start the engine).
Connect the TPMS scan tool to the vehicle’s OBDII port in order to upload the sensor ID. The TPMS scan tool and/or the vehicle dash will display a confirmation once the process is complete, which may take upwards of one minute. Note: If your TPMS scan tool is not capable of performing this process, the vehicle must be driven in order to complete the relearn.
GM KEY FOB RELEARN
NOTE: Not all GM vehicles are enabled from the factory with the key fob vehicle relearn initiation method.
Place the vehicle in Park of Neutral and secure the vehicle.
Ignition ACC or ON (do not start the engine).
Press and hold the unlock and lock buttons on the key fob at the same time. When you hear two horn honks, this indicates that the vehicle has entered the relearn mode.
Using your TPMS scan tool, trigger each wheel sensor, starting with the LF and working clockwise (LF, RF, RR, LR). The turn signal lamps will illuminate as you go. As each sensor is triggered and the sensor ID is captured, you should hear a single horn honk. If the vehicle is equipped with a sensor in the spare tire, be sure to trigger that wheel’s sensor as well (typically after triggering the LR).
When relearn is complete, you’ll hear two horn honks. A “Relearn successful” message may also be displayed on the driver information center.
UNIVERSAL AND MULTI-APPLICATION SENSORS
The OEs, in their usual fashion, have created an incredibly vast proliferation of pressure sensors (there are no industry standards, so everybody apparently felt the need to devise their own proprietary sensors in terms of data transmission protocol, with an estimated 75 versions currently in OE use, and upwards of 200 total OE sensor numbers). As a result, it’s impossible (or least extremely impractical) for any shop to stock enough sensors to accommodate all makes/models/years (you’d go broke just trying to stock these things in an attempt to achieve full coverage).
The solution: universal and multi-application tire pressure monitoring sensors. These sensors consolidate a large number of applications into far fewer sensors than you would otherwise need with OE sensors. Currently there are a number of sources for universal and multi-application sensors, but here are some of the most popular choices in the marketplace: Continental’s VDO REDI-Sensor, Schrader’s EZ Sensor, Alligator’s Sens-it and 31 Incorporated Systems Smart Sensor Pro+.
While none of these sensors will accommodate 100% coverage, we’re told that they will cover roughly 85-90% of the current market. The sensor makers are continually working to validate their sensors on additional vehicles, so with some of the remaining uncovered applications, it’s only a matter of time.
CONTINENTAL VDO REDI-SENSOR
This sensor is designed to cover all (available) protocols in a “shotgun” approach. The sensor is already pre-programmed with all system protocols. It sends out the ptotocals, allowing the vehicle’s ECU to grab the one that fits. These sensors are pre-programmed, and are not programmable (similar to a read-only CD that can’t be over-written). Basically, install and go.
The up-side: the sensor is already programmed with multiple protocols, so no programming is needed. The down-side: You can’t update it with new programming in the future (if a newer/different protocol is required).
This sensor was jointly developed by Schrader and Bartec (Bartec has long been involved in TPMS, making test/verification equipment for OE vehicle production, and now offer hand-held units for shops). The sensor is “blank” (like a blank CD), requiring a Bartec TPMS tool for programming. The tool reads data from the original sensor (reading the sensor’s “fingerprint”). A new EZ-Sensor is then placed in the tool’s cradle. The tool then imprints the original sensor’s info (it’s fingerprint) into the new universal sensor, in effect, creating a replicate (clone). If you screw up during the imprinting process, you can start over, since the EZ-Sensor is “re-writable.” In order to implant the original sensor’s info onto the new blank sensor, the Bartec tool is required. However, down the road during future service, any TPMS tool may be used if vehicle ECU relearning is needed.
The up-side: The sensor is easily programmable and can be re-programmed at whim.
The down-side: This sensor is dedicated (for programming) for use with only the Bartec tool, and the tool must be updated annually at a cost of about $300/year (in order to update the programming capabilities to meet ever-changing OE vehicle protocols).
31 INCORPORATED SMART SENSOR PRO+
The Smart Sensor Pro+ offers a complete TPMS solution, requiring only two sensor part numbers for 90% industry coverage, the ability to program a Smart Sensor in a matter of seconds, and the ability to copy the original OE sensor’s ID into a Smart Sensor. The company also offers their Pro+ TPMS scan tool, which is updateable at www.smartsensorupdate.com. Group 31 Incorporated also offers a complete line of TPMS materials, including X-tra Seal TPMS service kits, a full array of TPMS tools and accessories, and the company’s new MULTIPRO multi-application TPMS sensors.
This system is so cool that my eyebrows twitched with excitement when I saw a demo.
The sensor is blank (again, like a blank CD). Programming id accomplished via the internet by going to the Sens-It website. A docking station pad connects to your PC via a USB cable. Simply lay the blank sensor onto the pad, go to the website, and follow the simple prompts. Enter the vehicle’s VIN to obtain the correct protocol info, assign a wheel location (a simple drag and click deal on the site’s illustration), and hit a button. The info uploads, and presto…the new sensor is now programmed for the vehicle. Here’s the really sweet aspect of using the VIN as the reference….during a production run of the vehicle, the OE may have changed the pressure sensor model from one run to another. By using the vehicle identification number, you end up programming the new sensor with exactly the same data as the original sensor that was installed during vehicle production.
The up-side: The sensor is easily programmed (and can be re-written up to about 15 times). The programming base (this plugs into the PC via a USB cable) runs a mere $199. In addition, protocol data is continually updated on the site (hourly), so you get the latest info at the moment instead of waiting for an annual update. Plus, the programming and updates are free. If you know how to use a mouse to click and drag, you can program this sensor.
The down-side: Your shop must have a PC and access to the internet in order to program the sensor and to obtain the continually-available free updates. As far as I’m concerned, this isn’t much of a drawback. If you don’t have Internet access at your shop, get out of the dark ages and get with it. Even if you don’t have a PC back in the shop area, simply use the boss’s computer. Programming only takes a few minutes.
Remember, as mentioned before, regardless of the brand of sensor, once programmed and installed, the sensors must then be relearned to the vehicle, even if only one sensor has been replaced.
TPMS SCAN TOOLS
44231 Phoenix Drive
Sterling Heights, MI 48314
100 Enterprise Dr.
Newcomerstown, OH 43832
655 Eisenhower Dr.
Owatonna, MN 55060
800-533-5338 (toll free)
31111 Wixom Rd.
Wixom, MI 48393
TPMS INFO/REFERENCE MATERIAL
Tire Industry Association
800-876-8372, ext 106
Mitchell1 (information in booklet form or software)
888-724-6742 (toll free)
Tire pressure monitoring systems aren’t just for the OE market
While it’s the absolute duty and responsibility of any vehicle driver to routinely check each tire’s condition and inflation pressure, in the real world, we know that this rarely happens, at least among the commuter masses. However, any racer (or his crew) understands the critical importance of tire inflation pressure, and checks are religiously performed. In the world of classic cars/collector vehicles/street rods/hot rods, we would hope that this critical factor is also recognized and dealt with routinely (or at least prior to each cruise or long trip).
It’s one thing to perform a “pre-flight” check by inspecting each tire’s inflation pressure with a gauge, but this doesn’t take into account the potential reduction or loss of pressure during vehicle operation (aside from the driver hopefully recognizing steering and handling feedback).
TPMS (tire pressure monitoring systems) are now mandatory on new OE vehicles. These systems continuously monitor inflation (and temperature) and alert the driver when one or more wheel locations experience a drop of pressure (and/or elevation of temperature) beyond a pre-set calibrated level. This is not only a worthwhile feature for the average dummy who never bothers to get off their lazy behind and check for themselves, but it’s a sensible safety feature to alert the driver that pressure is dropping during a drive cycle. Naturally, we should be able to assume that a seasoned driver will feel a pressure drop (to an extent) if the vehicle begins to pull right or left, or if the steering begins to feel “heavy.”
There are two basic types of TPMS available as retro-fit kits. One style features screw-on “cap” style sensors that simply thread onto the existing valve (no need to dismount the tire to install a new valve assembly). The other style more closely mimics the OE approach, involving a valve-sensor for each wheel. This valve-sensor replaces the existing air valve. The sensor is integrated into the valve assembly. Either type of system features a receiver and mountable display unit (which may be dash mounted or fitted to the interior in whatever creative manner you see fit). In either case, the required wiring for the installation is minimal.
Monitors/display units are also available (depending on the specific system) for either in-car mounting or as a remote (battery powered) device that you can slip into your pocket and/or mount into an available clip-on or slip-in mounting base.
At the time of this writing, the only available TPMS retrofit kits appear to be Schrader’s AirAware kit, SigmaAuto’s kits and HawksHead’s Track Master.
SigmaAuto offers four TPMS systems that apply to the 4-wheel passenger car market, including their TyreDog TD-1000A, TireMinder TMG300C, Accu-Pressure and Tire SafeGuard systems.
Both the TyreDog and TireMinder feature sensors that simply screw onto the wheel’s valve in place of the existing cap (no need to dismount the tire to install the sensors). Each of these systems features a battery-powered wireless monitor that may be mounted in the interior location of your choice.
The Sigma Accu-Pressure and Tire Safeguard systems feature traditional OE-type sensors that replace the existing air valves (these sensors feature both the air valve and sensor in one package). The monitor installs in the interior. Both the Tire SafeGuard model and the Accu-Pressure model receivers require hard-wiring to a 12V source (includes accessory plug).
Regardless of which system is selected, due to the weight (however minimal) of the pressure sensors, the wheel/tire assembly should be balanced after sensor installation.
The Tyredog TD-1000A sells for about $289.
The TireMinder TMG300C sells for about $249.
The AccurPressure lists for about $209.
The Tire Safeguard lists for about $289.
The AirAware retrofit kit includes four wheel-mounted “traditional OE style” sensors that double as air valves and sensors. Apparently, the monitor is powered by two AA batteries but may be hard-wired as well. However, many of the reports I’ve read complain about low sensor battery life (which seems strange, considering that fact that Schrader makes replacement OE sensors). Two models are available, including P/N 20256 (battery powered monitor) and 20257 (hard-wired). I’ve seen the P/N 2-257 ranging in the $160 to $200 range. During my research, all of the listings that I found for the 20256 show this as “no longer available,” and I’ve been unable to verify this through Schrader.
This system features simple screw-on sensors that replace the existing valve caps (these systems now include a set of four stubby metal tire valves to be used at installer discretion…use their valves or use your existing…your choice). The screw-on valve cap installation allows use with either tubeless or tube tires. These sensors monitor both air pressure as well as internal air temperature. Warning settings are adjustable and can be programmed for psi, Fahrenheit, Centigrade, etc. The monitor is also optioned for illumination for night use. Sensor battery life is rated at one to two years. Replacement sensor batteries require CR1632 3V button-type batteries. The monitor can be powered by either its own rechargeable power pack or hard-wired to 12V. According to the maker, the ease of application allows quick interchanges between vehicles and different sets of wheels and tires.
The monitor features a low-battery alarm and reduces 12V to 5V DC. If using the power pack (instead of hard-wiring to 12V), a fully charged monitor battery should last for about two weeks.
The monitor features three buttons. The center button is the SET command. The left button scrolls UP and the right button scrolls DOWN.
During initial setup, press the SET button for five seconds. The monitor will beep and will enter the Pressure Setting Mode.
The monitor will flash the left front tire position. Press the left or right button to scroll to the desired pressure setting. Once the left front tire pressure warning is selected, press the SET button again. The display will then move to the right front wheel position. Repeat (in order of left front, right front, right rear and left rear) until all wheel positions have been adjusted for the desired PSI settings.
Wheel sensors should be lightly lubricated with anti-seize compound and installed finger-tight. The weight of the sensors is minimal and should not require wheel re-balancing.
If you’ve re-adjusted the pressure settings on all four wheel positions, upon restarting the system, it make take up to four minutes for all sensors to be detected by the system.
Further instructions are provided with the kit regarding system operation and adjustment modes.
This is a fairly straightforward TPM system that doesn’t require tire dismounting/mounting.
The Trackmaster kit sells for about $225 (depending on the distributor).
INSTALLATION OF A TYPICAL VALVE/SENSOR SYSTEM
Using Sigma’s Tire SafeGuard system as an example, installation is fairly simple. The receiver and monitor display consist of separate pieces. The monitor display may be mounted remotely (using an available stand or installed with adhesive-backed Velcro); or the display unit may be mounted directly to the receiver. In either case, the display is connected to the receiver with a single wire, and the receiver is then powered by a 12V source (plug into a 12V power port, or hardwire). If hard-wiring, connect the red wire directly to a constant-on hot 12V source. Connect the yellow wire to a switchable 12V source, and connect the black wire to ground.
The mounting location of the display monitor is up to you. You can clip it onto a visor or use a Velcro stand on a convenient flat surface; or you can be creative and fabricate a housing or recess in an available panel area.
Once the receiver and monitor have been installed, turn the ignition to the on position and verify that the LCD display lights up (it should display the four tire positions).
Turn the ignition switch off and proceed with sensor installation.
Demount the tires from the wheels. Remove the existing air valves and discard. Carefully clean the air valve port area on the wheels, removing any dirt or other debris.
Note that the new TPMS sensors are labeled (No. 1, No. 2, No. 3 and N0. 4). For first-time sensor installation, install the sensors to the wheels as follows:
Sensor No. 1 Right front wheel
Sensor No. 2 Right rear wheel
Sensor No. 3 Left rear wheel
Sensor No. 4 Left front wheel
When packaged, the sensors are intended for the afore-mentioned wheel positions (the receiver is already programmed for those locations). In the future, you can easily re-program when rotating wheels/tires.
In order to aid in accommodating various wheel designs, the sensor valve stem can be angle-adjusted. Insert the stem into the sensor body. Remove the stem sleeve (insert the small steel pin provided in the kit to hold the stem while unthreading the sleeve from the stem).
Insert the sensor and stem into the wheel, with the stem protruding through the valve hole. Determine and adjust the stem angle to suit your wheel. Tighten the small set screw at the rear of the sensor body to secure the stem to the sensor body. Place the supplied washer onto the exposed stem at the outside of the wheel surface, and install the threaded sleeve onto the stem. Using a socket wrench, tighten the sleeve onto the stem while using the steel pin in the stem base to hold the assembly (to prevent it from rotating). Tighten the sleeve to a value of 12 ft.-lbs. DO NOT over-tighten, as this can damage the sensor and/or create an air leak.
Re-mount the tire to the wheel. Use care to prevent contacting the sensor with a tire iron during mounting! Also make sure that the tire bead does not smash into the sensor during mounting.
Inflate to your specified pressure and install the wheel packages to the vehicle.
RE-TRAINING THE SYSTEM
Again citing the Sigma valve-sensor type system as an example, in the future, if you rotate wheels to different positions on the vehicle, you’ll need to re-program in order for the display to retain the correct wheel position for each sensor. Otherwise, if sensor No. 1 (originally at right front) is moved to, say, the right rear, and pressure goes down on that tire, the display will show the right front as the culprit, per it’s original program.
The re-training is simple. With the ignition in the on position, release 3 psi or more from the right front tire. This triggers its sensor to emit a signal to the receiver. The receiver then sets up this wheel/tire as the system’s new No. 1 sensor. The system then moves on to the No. 2 tire, where you repeat the same procedure. Always re-program by following the 1 – 2 – 3 – 4 sequence (RF, RR, LR, LF).
An alternate method is to place the system into its retraining mode. Follow the setup order and release air from each tire for about 20 seconds. After removing air from the last tire (LF), the re-training is automatically completed. If the ignition is turned off at any point during the reprogramming, the setup is canceled and you’ll need to start over.
Re-inflate all tires to your specification.
Average cost for a retro-fit system is in the mid-$200+ range, and even the most labor-intensive installation is relatively easy. You don’t need to have an advanced degree in electronic engineering. Depending on the system you choose, the monitor can either be installed to the vehicle interior or used as a pocket-stored remote device. Sensor choices include screw-ons to the existing air valves or require tire dismounting to install a combination valve/sensor to the wheel. Programming is easy. Just follow the instructions. Once in a while, technology actually works for us instead of against us. If you have any sense of “feel,” you should be able to detect a reduction of air pressure in a single tire (heavy steering, pull, etc.). If you don’t want to rely on your senses, a TPMS will alert you to the situation.
CURRENT SOURCES FOR RETROFIT KITS
800-345-0578 (cust. Service no.)
Monolith International Trading
440 Middlesex Rd. #118
Tyngsboro, MA 01879