Diesel exhaust aftertreatment systems are required for meeting Final Tier 4 emission regulations. This paper addresses an aftertreatment system designed to meet the Final Tier 4 emission standards for nonroad vehicle markets. The aftertreatment system consists of a fuel dosing system, mixing elements, fuel vaporizer, fuel reformer, lean NOx trap (LNT), diesel particulate filter (DPF), and an optional selective catalytic reduction (SCR) catalyst. Aftertreatment system performance, both with and without the SCR, was characterized in an engine dynamometer test cell, using a 4.5 liter, pre-production diesel engine. The engine out NOx nominally ranged between 1.6 and 2.0 g/kW-hr while all operating modes ranged between 1.2 and 2.8 g/kW-hr. The engine out particulate matter was calibrated to approximately 0.1 g/kW-hr for various power ratings. Three engine power ratings of 104 kW, 85 kW and 78 kW were evaluated. Test results on aged catalysts show that the system performance met Final Tier 4 emission standards having NOx levels below 0.4 g/kW-hr under a range of test conditions that were reflective of actual vehicle operation. Aftertreatment performance was characterized under multiple testing conditions including the nonroad transient cycle (NRTC), ramped 8-mode cycle and a variety of steady state operating points to ensure all not-to-exceed (NTE) regulations were met. LNT regeneration, LNT desulfation and DPF regeneration were demonstrated in these test cycles while maintaining repeatable and consistent aftertreatment temperature control. Final Tier 4 emission standards were met with low fuel usages for LNT regeneration ranging between 1.4 and 3.1%. The aftertreatment system reduced NOx by 89% on the NRTC and 87% on the ramped 8-mode cycle. Likewise, a system without the SCR catalyst yielded similar results of 88% NOx reduction on the NRTC and 86% on the ramped 8-mode cycle. Both system configurations met Final Tier 4 emission levels.