An apparatus is provided for determining a tire operating condition including a tire-based pressure and temperature sensor and transmitter and a vehicle ignition system. A vehicle-based receiver/controller receives sensor signals and state of the ignition system. The controller provides an error signal when the sensed tire pressure is less than a set threshold value Pset and resets the error signal when the sensed tire pressure is greater than a reset threshold value Prst. The receiver/controller determines the set threshold value Pset and the reset threshold value Prst as a function of a calculated warm tire pressure value Pwarm, determines a mole value N of the tire pressure, and adjusts the determined set threshold value Pset and the reset threshold value Prst in response to the vehicle ignition state and a change in the determined mole value N. A display is provided for displaying the error signal.