Well since Evo X and every 2008 vehicle has TPMS in it I might as well edumacate you guys on this
A tire pressure monitoring system, also referred to as TPMS, 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 radio signal to the system's antenna and receiver, which then sends a digital signal to an ECU. Note that some vehicles are equipped with one central antenna, while others feature individual antennas in the wheel wells at each corner.
A direct tire pressure monitoring system -- one in which a dedicated system exists that monitors actual tire inflation pressure -- is generally calibrated to alert the driver when one or more tires have lost at least 20% to 25% of the programmed/recommended inflation pressure.
In most instances, if a "fault" signal is processed by the ECU, the in-dash tire pressure warning light will illuminate, while if a tire pressure problem is indicated, the warning light will illuminate constantly. If the light blinks, as it does in many newer OEM systems, it indicates a system fault that must then be diagnosed with the proper diagnostic tool.
It's important to note that whenever sensors are moved to new locations (during wheel rotation, etc.), the individual sensors may need to be re-programmed or re-set 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 re-set).
TPMS components
Two basic "styles" of TPMS sensor/transmitters are available: banded and stemmed. (The correct OEM term for the sensor is wheel mounted sensor.)
Banded sensors are affixed to the inside of the wheel using both a positioning adhesive (peel off) and a band clamp. Stemmed sensors feature the valve stem as an integral part of the sensor. The sensor mounts via the wheel's valve hole and is secured with a mounting nut. Depending on the maker's design, these wireless pressure sensors transmit their data to an ECU using either AM or FM signals, usually in the 125 kilohertz range.
Five primary sources for OEM tire pressure monitoring systems include Schrader Electronics Ltd., Beru AG, Pacific Ltd., Siemens AG, TRW Automotive, etc. Schrader systems are found on Ford, Chrysler, GM and Nissan/Infiniti applications. Pacific systems are found on certain Toyota (including Lexus) and Honda vehicles. Beru systems are used on Mercedes, Porsche, BMW, Audi/VW and Land Rover models.
Since the OE transmitters are the stem type, the wheels are designed to accommodate these units (the valve stem hole area is configured for these transmitters). Some aftermarket wheels do not allow the addition of the stem-type transmitter, which makes them suitable for a band (strap-on) type.
The vast majority of OE tire pressure monitoring systems are stem-mounted as opposed to band-mounted. The primary reason involves diagnostic capabilities. If the sensor is band-mounted and deeper inside the wheel, it's more difficult for the signal to pass to the diagnostic tool, whether the system uses an RF signal or a magnetic signal.
Stem-type sensors are light, weighing in the neighborhood of about an ounce, so this won't be a problem regarding wheel balance compensation.
Most direct type pressure sensors are powered by a lithium battery with an expected lifespan of seven to 10 years. Many of them are designed to operate only during or after a 20 mph-plus driving experience. When the vehicle is parked, the sensors are usually designed to transmit pressure only once per hour or so, in order to preserve battery life.
Who needs a TPMS?
Are tire pressure monitoring systems really necessary? Some might say that these systems are a waste of money, arguing that if people would simply check their tire pressures on a regular basis, there would be no need for an on-board monitoring system. But, therein lies the rub. Most people don't bother checking inflation pressures, at least not as often as they should.
Aside from protecting people from their own ignorance, tire pressure monitoring systems do make sense for a number of reasons.
1. They provide safety. Even for those who recognize the importance of tire pressure and routinely perform a manual check, it's nice to be alerted to a drop in pressure before the tire fails. It doesn't matter whether the drop results from a puncture, faulty valve or chuckhole tear.
2. They protect run-flat tires. Another example of the need for a TPMS lies in the design of run-flat/zero-pressure tires. Many of the run-flat tires on the market are constructed so superbly that a drop in pressure may not be discernable to the driver. So it's vital to have a system in place that alerts the driver of a low pressure problem in an effort to prevent tire damage and avoid a traffic mishap.
Regardless of personal opinions on the matter, we really don't have a choice. After Aug. 31, 2007, all new model four-wheeled vehicles weighing 10,000 pounds or less must be equipped with tire pressure monitoring systems. This means that the aftermarket service industry must be able to handle these systems properly and diagnose system problems.
Indirect systems
As a relatively inexpensive method of altering the driver to a low tire pressure situation, some OEM vehicles obtain this information not through a dedicated direct tire pressure monitoring system, but rather by using information already monitored by the anti-lock braking system. This is referred to as an indirect TPMS.
A "low" tire will rotate at a different rate than properly inflated tires (due to a difference in rolling tire diameter); this difference in wheel rotation is sensed by the ABS. A signal is then sent to alert the driver via a warning light. It's then up to the driver to check all four tires to determine which is under-inflated.
This approach has its problems. Faulty alerts can easily result if the wheels slip on an icy road, or if inside and outside wheels rotate at different speeds during sharp turns, because ABS monitoring interprets a difference in rotation as a low pressure condition. In addition, if all four tires are equally under-inflated, the ABS won't trigger the pressure warning, since all wheels are rotating at the same speed.
In general, indirect tire pressure monitoring systems are designed to illuminate the warning light when a single tire's recommended inflation pressure has dropped by about 30%.