Recent studies show that plug-in hybrid electric vehicles (PHEVs) show a large gap between real-world and official type-approval CO2 emissions. The gap is to a great extent attributed to less frequent charging than anticipated by the type-approval regulation, but also to the use of heating and air-conditioning, which are not assessed during type-approval. This study assesses, via testing of a representative PHEV, the effect of ambient temperature and use of air-conditioning on CO2 emissions, electric energy consumption, and electric ranges. The vehicle was also tested using different plug-in hybrid operating modes to evaluate their effect on the CO2 emissions. Furthermore, it was assessed how on-board fuel- and energy-consumption monitoring (OBFCM) data recorded by the vehicle during the testing program can be used for determining the real-world usage of PHEVs.