The impact of oil-derived catalyst poisons on the FTP performance of a LEV configured with two different catalyst systems was studied. One of these catalyst configurations was composed of a single underfloor Pt-Rh converter while the other was composed of a Pd lightoff catalyst close-coupled to the exhaust manifold and a Pt-Rh catalyst located underfloor. Both configurations were aged to approximately 100,000 miles on vehicles and were then evaluated for FTP emissions performance. The oil-derived poisons were then selectively removed using a wet chemical method, and following this the catalyst systems were again evaluated for FTP performance.In the lightoff and underfloor catalyst system, removal of the oil-derived poisons improved the FTP Cycle 1 and Bag 1 HC tailpipe emissions significantly. Although Bag 2 and 3 emissions are also improved, the absolute g/mi improvement in this latter case contributes very little to the overall FTP emissions. These results are consistent with earlier laboratory studies of this type of catalyst system which predicted that oil-derived poisons selectively impact the front-most catalyst element and should consequently impact HC and CO lightoff performance. The oil-derived poisons were also found to significantly impact the HC, CO and NOx lightoff performance in the underfloor-only catalyst system. The relatively large impact observed with this catalyst system may be attributable to the optimization of the vehicle for LEV emission standards, resulting in an increased sensitivity of the system to deterioration effects previously considered minor or insignificant in older generation Tier 0 or Tier 1 emission systems.