Measuring the actual value of pressure is done in two steps:
1. TPMS_READ_PRESSURE(gu16UUMA, 1u) will store the 10-bit uncompensated value of pressure (output of the ADC) in UUMA.
2. TPMS_COMP_PRESSURE(&u16CompPress,gu16UUMA) performs a compensation of the pressure value stored in UUMA: the function linearizes the value and correct the error due to temperature and voltage (this is why this function must be called after the readings of pressure, temperature and voltage).
Both functions (READ and COMP) return a status to indicate if the pressure value is ok or if there has been a problem with the ADC or an underflow/overflow.
What is important to do is to check the returned status to know if the pressure value is ok or not. The returned status is explained in the firmware user guides. For example, below is the returned status of TPMS_COMP_PRESSURE: