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Due to a need for a robust measurement system for on-board real-world vehicle emission measurement, a heated ND-IR(h-NDIR) technique has been developed and evaluated for its potential. The h-NDIR is capable of measuring CO and CO2 under wet-based condition by correcting interference from co-existing gas with an algorithm specially developed for the present study. The resulting H2O interference to the CO2 measurement is less than 0.01vol% for zero point and less than ±1% for span points and that of CO measurement is less than 0.001vol% for zero point and less than ±2% for span point against 0 to12vol% H2O. An on-board emission measurement system using the h-NDIR in combination with an Annubar® flow meter and an air to fuel ratio sensor has been evaluated. The result reveal correlation between the present system and a chassis test system to be within 7% for fuel consumption, within 5% for CO mass emission, and within 6% for CO2 mass emission.