The accumulation of ash in a Diesel Particulate Filter (DPF) eventually results in an increase in the pressure drop across the exhaust system component. This situation translates into a reduced capacity for soot, and requires an increased frequency of active regenerations to eliminate this soot. For heavy duty diesel applications, the lifetime of the DPF is long enough to expect that cleaning of the ash from the DPF will be required. The physico-chemical characteristics of the ash as a function of temperature and time will have an impact on the effectiveness of this cleaning. To develop a deeper understanding of this subject, four different samples of ash were characterized in this study that were collected under active or passive regeneration from exhaust systems of engines running on different fuels: ultra low sulfur diesel (ULSD), and biodiesel fuels B20 and B100. The lubricant, an API CJ-4 oil, was used for each engine test. The formulation of engine lubricants along with the DPF regeneration and ash cleaning strategy may impact the size, chemistry, morphology, deposition and distribution of ash deposits in the DPF. Composition and morphology of ashes from active and passive regenerated DPF exhibited significant differences. The passive ash showed a greater change in morphology in response to heat treatment than the active ash. Additionally, significant phase changes (measured by XRD or thermal analysis) were observed in passive ash that was sintered after recovering from the DPF relative to actively regenerated ash. However, the actively regenerated ash exhibited only minor phase changes upon sintering. The main components of the ash were identified as calcium sulfate, and various zinc / magnesium / calcium phosphate phases; except for DPF ash engine test that was fueled with off-spec B100 which had lime, periclase and some sodium phosphate upon sintering (derived contaminants from direct combustion of the biodiesel fuel or from the biodiesel fuel dilution in the crankcase engine oil).