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An increasing discrepancy between real-world and type-approval fuel consumption for light-duty passenger vehicles (LDPVs) has been reported by several studies.Normally,real-world fuel consumption is measured primarily by a portable emission measurement system.The on-board diagnostic (OBD) approach,which is flexible and offers high-resolution data collection,is a promising fuel consumption monitoring method.Three LDPVs were tested with a laboratory dynamometer based on a type-approval cycle,the New European Driving Cycle (NEDC).Fuel consumption was measured by the OBD and constant-volume sampling system (CVS,a regulatory method) to verify the accuracy of the OBD values.The results of the OBD method and the regulatory carbon balance method exhibited a strong linear correlation (e.g.,R2 =0.906-0.977).Compared with the carbon balance results,the fuel consumption results using the OBD were 7.1％±4.3％ lower on average.Furthermore,the real-world fuel consumption of six LDPVs was tested in Beijing using the OBD.The results showed that the normalized NEDC real-world fuel consumption of the tested vehicles was 13％±17％higher than the type-approval-based fuel consumption.Because the OBD values are lower than the actual fuel consumption,using a carbon balance method may result in a larger discrepancy between real-word and type-approval fuel consumption.By means of the operating mode binning and micro trip methods,a strong relationship (R2 =0.984) was established between the average speed and relative fuel consumption.For congested roads (average vehicle speed less than 25 km/h),the fuel consumption of LDPVs is highly sensitive to changes in average speed.