Keeping an Eye on PSI:
Tire Pressure Monitoring Systems, Part 2
By Tom Nash, AAM
Federally mandated tire pressure monitoring systems are here. Are you prepared to service vehicles with TPMS?
Editor's Note: Last month, Part 1 of this article discussed the importance of the TREAD Act and how it's addressing the growing concerns regarding major recalls of defective and improperly inflated tires. The article discussed the two basic types of TPMS and gave tips on how to properly service TPMS. In Part 2, we learn about the correct tools used in servicing TPMS.
Handheld TPMS Tools
The basic tool for servicing tire pressure monitoring systems (TPMS) is a handheld device for registering each wheel sensor/transmitter with the TPMS module. Many of these tools are available. Among different features available in the tools are the completeness of the application coverage internal database, upgradeability, memory storage of recent readings and the ability to connect to shop computers. Other desirable features are ease of use, a good user manual and visual/sound function indicators. Because different brands and styles of sensors vary in the frequency at which they operate, make sure you purchase a tool that functions with all sensors and frequencies.
Scan Tool Kits
Many kits are available for adapting scan tools for TPMS service. Every major scan tool maker has such a kit to not only test and register wheel sensors, but also perform TPMS module or ECU reprogramming and reset the TPMS warning light or malfuntion indicator light (MIL).
Valve Core Torque Tools
Valve stem TPMS sensors are precision devices and therefore fragile. A special valve core torque tool should be used if you need to remove the core - even though
it is not recommended. These tools are widely available and inexpensive.
Here are but a few of the sources for TPMS tools:
- Bartec USA, www.bartecusa.com
Bartec USA offers a range of tools for TPMS service, including its Wheelrite Tech 300 plus model.
- Snap-on Diagnostics, www.diagnostics.snapon.com
Snap-on's TPMS1 is upgradeable and covers all current applications.
- K-Tool International, www.ktool.com
The T.I.P.S. tool provides both a visual and audible confirmation that the sensor has been triggered and is transmitting.
- OTC Tools, www.otctpms.com
The No. 3833 Tire Pressure Monitor tool kit includes accessories and manuals.
TPMS Service Tips
Here are some tips and hints to remember when servicing vehicles equipped with TPMS:
- Use an accurate pressure gauge - Reading accurate pressures is critical for TPMS. You must have a quality, properly calibrated tire gauge.
- Cold weather - A drop in temperature during cold weather will cause tires to deflate as the air inside them contracts. This may cause the TPMS warning light to illuminate. Adjust the tire pressure accordingly. If the tire pressure is adjusted inside a warm shop (60 F to 70 F) and the outside ambient temperature is much colder, add an extra one psi for every 10 degree Fahrenheit difference.
- Tire rotation - Tire rotation demands that all tires be re-registered with the TPMS control module, using an ID code-registering tool.
- New tires - Changing to tires that are not the same as the originals may, or may not, affect the operation of the TPMS, depending on the pressure range of the tire. Logically, tires with a lower pressure range than the original tires will set off the TPMS warning light. Be sure to reinstall the TPMS wheel sensors in their original positions or you'll have to reset the system.
- Changing to spare tire - When removing a flat or damaged road tire with a TPMS wheel sensor and installing a spare tire that is not equipped with TPMS, the warning light will illuminate and flash until the original or new road tire is reinstalled and the ID code is re-registered with the TPMS control module.
- Mounting tires to wheels - Special care must be taken when removing or mounting tires to wheels equipped with TPMS sensors. The sensors can be easily damaged or destroyed if direct leverage is applied to the stem or sensor body. The air should be bled from the tire and the valve pushed into the tire before breaking the tire away from the wheel.
Note: The air should be bled by depressing the valve core. The valve core should not be removed from the valve as the use of a special valve core torque tool is required to avoid overtightening the valve, which would result in failure of the pressure sensor.
Tires should always be mounted using a tire changer to ensure proper fit and prevent breaking the sensor/transmitter. After filling the tire to the correct pressure, install the wheel to the vehicle and register the transmitter ID to the TPMS control module, if needed.
- Filling tires - When filling any tires the air supply should be clean and dry. This is exceptionally critical for TPMS tires as any sediment or moisture can affect the precision workings of the sensor and transmitting devices. Take care to blow off the area around the valve stem to rid the area of dirt. If a valve stem does not have a cap, gently blow air into the valve to remove any dirt or dust.
- Aerosol inflators with sealant - Using a can of aerosol tire inflator with sealant is not an option for TPMS. The gummy sealant will clog up the valve and pressure sensing port of the wheel sensor. The warning light will illuminate and you'll end up replacing the sensor.
- Sensor battery life - The tiny integrated lithium battery in the wheel sensor has an estimated life of 10 years or 100,000 miles. When a sensor battery voltage gets to the low limit, it may cause the TPMS control unit to generate a diagnostic trouble code. If one sensor battery is low, the others are sure to follow shortly. If any tire work is performed as the vehicle nears the 10-year or 100,000-mile mark, it would be good preventive maintenance to replace the sensors.
- Wheel Sensor/Control Module Communication - Triggering the sensor on a valve stem-mounted system is accomplished by holding the tool to the tire sidewall close to the sensor body, which is inside the tire, below the valve stem.
Band-type sensors are strapped in the valley of the rim, 180 degrees away from the valve stem. The best way to trigger them is by holding the tool against the tread at that location.
Some TPMS systems use a control module mounted under the driver or front passenger seat. With these vehicles, warn customers to never place metal objects - such as tools or aerosol spray cans - near the TPMS control module, as these items may interfere with the signal reception from the wheel sensors. Also, the valve stem of the wheel sensors serves as the transmitting antenna, so don't replace the original valve caps with any other that would interfere with the signal.
- Clearing TPMS Codes - Erasing TPMS diagnostic trouble codes (DTCs) and resetting the control module is accomplished by the use of a scan tool. Because the TPMS diagnostic procedures for each model vary and would be too lengthy to include here, refer to the specific service information for the vehicle you are servicing.
- Key Fob Reset - Some models have TPMS reset systems that require pushing a button on the remote keyless entry (RKE) key fobs. These are usually found on older vehicles with indirect TPMS. The problem with this type of reset procedure is that an accidental push of the button may cause the TPMS to recognize the current pressure levels as normal and correct, when in fact, any or all tires may be underinflated.
| Tom Nash, AAM, a veteran automotive industry writer, is a freelancer whose firm, Blue Car Media, is in Sterling Heights, Mich. He is a 2005 graduate of the Automotive Management Institute, from which he received his Accredited Automotive Manager designation. His e-mail address is firstname.lastname@example.org.
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