Yes. The regeneration process leaves residual sulphated ash as a by-product of combusted engine oil. The main purpose for performing a basic pneumatic cleaning is to purge the residual ash from the cells of the DPF. In addition, the efficiency of a vehicles’ regeneration is dependent upon its duty cycle. Most vehicles operating conditions don’t promote perfect regeneration that would ensure that a DPF is completely purged of unburned PM (particulate matter) therefore must be cleaned periodically.