Due to raising interest in diesel powered passenger cars in the U.S. in combination with a desire to reduce dependency on imported petroleum, there has been increased attention to the operation of diesel vehicles on fuels blended with biodiesel. One of several factors to be considered when operating a vehicle on biodiesel blends is understanding the impact and performance of the fuel on the emission control system.This paper documents the impact of the biodiesel blends on engine-out emissions as well as the overall system performance in terms of emission control system calibration and the overall system efficiency.The testing platform is a light-duty HSDI diesel engine with a Euro 4 base calibration in a 1700 kg sedan vehicle. It employs 2nd generation common-rail injection system with peak pressure of 1600 bar as well as cooled high-pressure EGR. The study includes 3 different fuels (U.S. ULSD -base fuel; and B5 and B20 prepared from soy-derived biodiesel) with two different emission control systems (ECS) (NOx adsorber catalyst (NAC) with a diesel particle filter (DPF) and selective catalytic reduction (SCR) with a DPF). The main focus of this paper is on NAC calibration, regeneration, and desulfurization; DPF regeneration and preliminary emissions, with a focus on oxides of nitrogen (NOx), and fuel economy results. The NAC ECS aged to end of life conditions and showed efficiencies in the mid 80% range, therefore allowing operation within the Tier 2 Bin 5 emission standards for both intermediate as well as useful life conditions.The development test results from the vehicle chassis tests showed some NOx benefits operating on B20 fuel blends with the NAC ECS. This is a result of the calibration work being performed using the 20% biodiesel fuel blend. The resulting higher exhaust temperatures with ULSD resulted in lower ECS effectiveness with the NAC. The average tailpipe results operating the vehicle on B20 were in the range of 0.03 g/mi, while the emissions with ULSD averaged below 0.05 g/mi with larger cycle-to-cycle variability.