Folks, there has been talk here before about the TPMS and what the system is, and why it doesn't report actual pressure of each tire. In the Fall 2009 issue of
Quattro Quarterly, Jim Benoit gives us the answer:
"A less complex system was introduced in 2005 in some models and is referred to as "low-line". Each wheel had its own battery operated sensor [in the tire valve], but only one antenna was used. The system did not know the location of each tire but only the ID number of each tire pressure sensor. It compared the actual value of the tire pressure to the stored value. if the value was lower, the warning light would illuminate. This system could only alert the driver that there was a tire that had low pressure but could not specify which one."
The new (2010 and beyond)
indirect tire pressure monitoring system works differently:
"The system [ITPMS] determines pressure loss based on two principles: wheel radius analysis and wheel spectrum analysis. To simplify, the ABS sensors can determine tire pressure loss by measuring the change of tire rolling diameter and the change in tire vibration as the tire loses pressure."
An advantage here is not extra parts, and the system can report each tires pressure individually.
Hopefully this clears up some of the discussion regarding TPMS and its current state.