Tier 4 / Euro IV emission norms for off-highway vehicles makes it mandatory for significant reduction in CO, HC, NOx and PM from the Tier III emission norms. The challenging levels of PM (Particulate Matter) are achieved by incorporating an After-Treatment Device which comprises of a DOC (Diesel Oxidation Catalyst) and a DPF (Diesel Particulate Filter). Since the DPF traps the soot, the particles get clogged inside the particulate filter and thereby causing a pressure drop and back pressure on the engine. The mechanism to remove soot particles without removing the particulate filter is by burning the soot, which is known as Regeneration. This paper describes the methodology to validate reliable performance of the After-Treatment system in field operations. The outcome from the analysis is not only instrumental in validation but also proves to be an important input in failure investigation and optimization for design and test engineers. The reports generated help the managers to draft risk mitigation plans for their vehicle groups.