Special tools make it easier to install and remove sensors. and also ensure that the nut and valve for the sensor are tightened to the correct torque.
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For mounting, technicians can choose either a clamp-in sensor (aluminium valve) or snap-in-valve sensor (rubber valve). Separate sensor versions are available for both types of valves (to ensure that the valve and sensor are compatible).
A snap-in valve is generally cheaper and easier to install than an aluminium valve. However, it should be considered that, because of the centrifugal force, a snap-in valve can not be used at speeds above 210 km/h. Aluminium valves are suitable for speeds > 210 km/h.
Please note: the valve should be inspected every time that tires are changed. This involves replacing the valve core, cap, nut, washer and seal. Component kits which contain the necessary spare parts are available for servicing sensors.
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 systems 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 ( 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.
Its 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 sensors wheel position.
Depending on the makers 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 wont 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 (Ive heard estimates as high as 10 years). However, since the use of these sensors is relatively recent, we really dont 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.
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 changedgrommets, 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.
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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 youre 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 dont 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 havent purchased a tester yet, youre wasting valuable time.
Exercise care during tire demounting to avoid sensor damage caused by a tire iron. In other words, dont 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 sensors retaining nut (clamp-on style) and dropping the sensor inside the tire. This keeps the sensor out of harms 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 entrys 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.
Dont replace wheel sensor parts haphazardly. Some sensors feature aluminum caps and nickel-plated cores. The end of the valve stem may serve as the sensors 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.
Here we present a variety of TPMS service tips provided courtesy of select manufacturers.
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