The Technicals

Next Article

Got gas?

Tire pressure monitoring systems

By Mike Mavrigian

We’ve discussed the subject of TPMS (tire pressure monitoring systems) in the past, but this is a topic that can always benef t 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.

Typical components of a “clamp-on” style sensor. The sealing washer seats against the inside surface of the wheel’s valve hole. The seal is placed at the outboard side of the hole, captured behind the hex nut.

DIRECT TPMS

A “direct” tire pressure monitoring system (where a dedicated system exists that monitors actual tire inf ation pressure) is generally calibrated to alert the driver when one or more tires have lost at least 20% to 25% of the programmed/recommended inf ation 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 inf ation pressure. The sensor then sends a radio wave signal to a receiver located in the vehicle. When inf ation pressure falls below a predetermined level, a warning light illuminates on the instrument cluster. Depending on the year, make and model of the 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 under-inf ated; or the warning system may indicate which location (LF, RF, LR, RR) is under-inf ated.

INDIRECT TPMS

Instead of monitoring actual inf ation pressure, an indirect system relies on the vehicle’s 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, if all four tires are under-inf ated by the same amount, the system may not detect a difference, and no alert warning may be provided. A direct TPMS is much 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.

To my knowledge, the indirect system was no longer is use in new vehicles as of 2007, when automakers switched over to direct systems.

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-on. Banded sensors are aff xed 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-on 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. been replaced, and that The snap-in style features includes both OE or aftera traditionally mounted market sensors, in order rubber valve style that to ensure that the TPM allows the valve stem to system functions propbe pulled through the hole erly. The only exceptions and “snapped” into place involve some Chrysler and similar to a traditional Mazda vehicles, where the valve. Always use the seals, valve core, nut and cap that come with replacement sensor(s) is

NOTE: When servicing any the new sensor. These compoautomatically relearned to TPMS sensor, do not use a nents are specif cally designed the vehicle during an inibrass valve core. This can for TPMS sensors. Never use tial drive cycle. result in dissimilar metal a brass valve core, as this can Other than these exceplead to electrolysis (reaction reaction and can lead to between dissimilar metals). tions, a TPMS scan tool is corrosion issues. Use only a required. stainless steel valve core. Whenever a valve NOTE: Since relearn procedures vary core has been removed, always replace it among automaker brands, it’s necessary to with a new core. Also, only install a valve determine the correct procedure for any cap that is designed for use with TPMS. This given vehicle before starting the relearn will likely be a plastic cap and will feature process. an internal O-ring for better sealing. The use of a steel or brass cap can also lead to CONDITIONS WHEREIN THE radio wave signal interference. SYSTEM MAY NOT FUNCTION RELEARN VS. PROGRAMMING 1. Similar radio frequencies in the imme

Vehicle relearn and sensor programdiate area may interfere with the system. ming are completely different procedures. 2. A radio device of similar frequency is Confusion is common due to the availbeing used in the vehicle. ability of aftermarket TPMS sensors that 3. Excessive snow/ice on the vehicle are offered as “programmable,” “universal” (especially around wheels and wheel wells) or “cloneable” sensor units. These senmay cause poor transmitter radio signal sors must be programmed with the proper operation. protocol/application information for the 4. The tire pressure warning valve subvehicle before they can be installed on the assembly’s sensor battery may be depleted. wheel. An exception is VDO’s Redi-Sensor 5. Wheels may be installed on the vehicle which does not require programming prior which do not feature a tire pressure monito installation (these sensors are already tor valve sub-assembly. loaded with the programming needed to 6. Use of studded snow tires or tire chains function with the vehicle’s system). may disrupt radio signals.

Regardless of the brand of sensor, once 7. If non-specif ed wheels are used, the programmed and installed, the sensors must system may not function properly because then be relearned to the vehicle, even if the radio waves are transmitted at different only one sensor has been replaced. It’s not angles from the pressure sensor. uncommon for shops to overlook the neces8. Depending on the type of tire used, the sary relearn step, proceeding under the system may not function properly even if assumption that the sensor programming the correct specif ed wheels are used. was all that was required. This misunPROPERLY derstanding can result in comebacks and NOTE: The average life of the grommet of customer complaints. the tire pressure monitor valve sub-assem

Vehicle relearn is a standard and manbly is about f ve years, at which time the datory procedure whenever a sensor has grommet should be replaced.

TIRE MOUNTING

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 specif ed torque value. Over-tightening can easily damage the stem.

When mounting the tire onto the wheel, install the inner tire bead f rst. 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 inf ated, recheck the valve nut and retighten to the vehicle manufacturer’s specif cation (this will likely be in the 35 in.-lbs. range. Valve stem damage can easily result from overtightening, so ALWAYS refer to the torque specif cations! Check for air leaks with a soapy water solution.

TPMS SENSOR RELEARN EXAMPLES

Following are a few examples of the steps required for TPMS relearn. If the replacement sensor(s) require programming, sensor programming must be performed prior to the relearn procedure. The following examples were provided courtesy of VDO for their Redi-Sensor.

FORD WITH PUSH-BUTTON IGNITION

Ford vehicles that are equipped with a push-button ignition switch require a specif c sensor relearn procedure. Once the replacement sensor(s) has been installed and all four wheels/tires are mounted to the vehicle, inf ate all tires to the recommended pressure and follow these steps: 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 the relearning procedure. 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 spare tire, be sure to trigger that wheel’s sensor as well (after triggering the LR). The TPMS scan tool is held at the tire valve/sensor during triggering. 7. Once the relearn process is complete, the vehicle horn will honk to conf rm.

GM VEHICLES EQUIPPED WITH DRIVER INFORMATION CENTER

This includes Camaros and other models that feature an information display on the dash.

1. Place the ignition in the ACC or ON position (do not start the engine). 2. Use the turn signal arm to display the inf ation pressures of all four tires. 3. Hit SET on the wiper arm to reset the

TPMS. 4. A screen pops up displaying “Are you sure you want to relearn?” At this point, push the wiper arm inward to toggle to

“YES.” At this time, the vehicle horn will honk twice to alert you to begin sensor triggering. 5. Using your TPMS scan tool, begin triggering the sensors, starting at the LF and working clockwise (LF, RF, RR, LR). Don’t forget to trigger the sensor in the spare tire if so equipped. You’ll hear a single horn honk as each sensor is successfully

triggered. You’ll hear a double-honk when the relearn procedure is f nished.

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.

1. With wheels/tires installed to the vehicle and inf ation pressure adjusted to specif cation, trigger all sensors using an OBD

II-compatible TPMS scan tool, starting with the LF and working clockwise (LF, RF, RR, LR). Trigger the spare (if so equipped) last. 2. Once all sensors have been triggered, place the ignition switch to the ACC or

ON position (do not start the engine). 3. Connect the TPMS scan tool to the vehicle’s OBD II port in order to upload the sensor ID. The TPMS scan tool displays a conf rmation once the process is complete, which may take several minutes. If your 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. (For reference, see www.autoserviceprofessional.com for the chart on applicable vehicles that can use the key fob relearn method.)

1. Ignition ACC or ON (do not start the engine). 2. 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. 3. 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. Remember to trigger the spare. 4. When relearn is complete, you’ll hear two horn honks. A “Relearn successful” message may also be displayed on the driver information center.

Before installing a sensor, make sure that the wheel well is cleaned of dirt, debris or oils.

UNIVERSAL 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). 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 tire pressure monitoring sensors. These universal sensors allow you to basically grab a new “blank” sensor and program it for the application. Currently there are three sources for universal sensors: Continental’s Redi-Sensor, Schrader’s E-Z Sensor and Myer Tire Supplies’ Sens-It.

While none of these universal sensors will accommodate 100% coverage, we’re told that they will cover roughly 85% to 90% of the current market. The makers are continually trying to obtain protocol information from the automakers, so if certain application information hasn’t yet been made available to the aftermarket, it’s a waiting game for the sensor makers.

CONTINENTAL VDO REDI-SENSOR

This sensor is akin to a universal TV remote control unit, in that it’s designed to cover all (available) protocols in a “shotgun” approach. The sensor is already pre-programmed with all system protocols. It sends out all frequency protocols (multiple data commands in a continuous wave), allowing the vehicle’s ECU to grab the one that f ts. These sensors are preprogrammed, 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). SCHRADER EZ-SENSOR

This sensor was jointly developed by Schrader and Bartec (Bartec has long been involved in TPMS, making test/verif cation equipment for OE vehicle production, and now offers hand-held units for shops). The

sensor is “blank” (like a blank CD), requirBy using the vehicle identif cation number, ing a Bartec TPMS tool for programming. you end up programming the new sensor The tool reads data from the original sensor with exactly the same data as the original (reading the sensor’s “f ngerprint”). A new sensor that was installed during vehicle EZ-Sensor is then placed in the tool’s cradle. production. The tool then imprints the original sensor’s The up-side: The sensor is easily proinfo (it’s f ngerprint) into the new univergrammed (and can be re-written up to about sal sensor, in effect, creating a replicate 15 times). The programming base plugs (clone). If you screw up into the PC via a during the imprinting USB cable. Protocol process, you can start data is continually over, since the EZ-Sensor updated on the site is “re-writable.” In order (hourly), so you get to implant the original the latest info at sensor’s info onto the the moment instead new blank sensor, the of waiting for an Bartec tool is required. annual update. Plus, However, down the road the programming during future service, and updates are any TPMS tool may free. be used if vehicle ECU The down-side: relearning is needed. Your shop must

The up-side: The sensor Any of the major TPMS scan tools can be have a PC and is easily programmable used for a relearning procedure. access to the and can be re-proInternet in order grammed at whim. to program the sensor and to obtain the

The down-side: This sensor is dedicated continually available free updates. Program(for programming) for use with only the ming only takes a few minutes. Bartec tool, and the tool must be updated annually at a cost of about $300/year (in DENSO SENSOR PROGRAM order to update the programming capaDENSO Products and Services Americas bilities to meet ever-changing OE vehicle Inc. has launched a TPMS sensor program protocols). with 16 part numbers covering more than 100 popular passenger cars, sport-utilities, MYERS SENS-IT trucks and crossovers, or more than 25 mil

This system’s sensor is blank. Programming lion vehicles on the road. is accomplished via the Internet by going to Additional DENSO TPMS sensor part numthe Sens-It website. A docking station pad bers will be announced later this year. connects to your PC via a USB cable. Simply Two DENSO TPMS sensor part numbers lay the blank sensor onto the pad, go to cover 73% of Toyota, Lexus and Scion vehithe website, and follow the simple prompts. cles, and an additional two part numbers Enter the vehicle’s VIN to obtain the correct cover 36% of Honda and Acura vehicles. protocol information, assign a wheel locaDENSO TPMS sensors maintain diagnostic tion (a simple drag and click deal on the capabilities, enabling quick and accusite’s illustration), and hit a button. The rate troubleshooting. Other benef ts are a info uploads, and presto... the new sensor is 10-year battery and quick, direct-f t instalnow programmed for the vehicle. Here’s the lation, with no need for time-consuming really sweet aspect of using the VIN as the cloning or programming. DENSO says its OE reference — during a production run of the experience ensures that First Time Fit senvehicle, the OE may have changed the pressors provide performance, reliability and sure sensor model from one run to another. f t. ●