In the ENSPIRIT FP7 European project framework a locomotive diesel engine aftertreatment pre-prototype, due to real-world testing difficulties, was realized directly downscaled and adapted for an automotive emissions laboratory testing. It is here reported how its NOx and PM2.5 abatement capabilities were determined testing two diesel engine passenger cars deprived of all abatement systems. With the first car the setup and performance of the ENSPIRIT® pre-prototype were optimized using several analyzers, even providing size distributions of ultrafine particles: final emission reductions, calculated in g/bhp-hr, of NOx by ~90% and of PM2.5 by ~60% were reached. The pre-prototype NOx and PM2.5 abatement capabilities were then validated with the second car and results have been compared with the ones from U.S. EPA Tier 4 non-road emissions standard. It was found a NOx emission reduction by ~90% and by ~50% for PM2.5, confirmed as statistically significant by applying the Student’s t-test.