Re: Tire pressure monitor accuracy
TPMSs are calibrated for sea level and are pretty accurate. The indicated TPMS tire pressure should be nearly the same as an accurate tire gauge at sea level.
The TPMS and PSIG reading will differ with altitude however (The TPMS is internal pressure, gauges are measuring relative pressure). At higher altitudes your tire gauge may indicate 40 psi (relative) where the TPMS indicates like 29 PSI and sets off the low pressure warning. There was a thread around here a year or two that went through the physics. A few drivers described their experience driving in high altitudes.
2011 WK2 Overland Mineral Gray/Black, Advanced warning, V8; 2009 KK Rocky Mtn V6; 2000 WJ Laredo I6; 1979 CJ7 I6... green... miles of smiles :)