Disclosed is a method pertaining to SCR systems for exhaust cleaning whereby liquid is supplied to a feed device via which it is supplied to a dosing unit at a consumption point of the SCR system. The method includes continuously determining cumulative amounts of liquid dosed via the dosing unit. Need for replacement or cleaning of a filter unit for said liquid is also determined on the basis of the cumulative amounts of liquid dosed. The method further includes dosing at least part of the liquid supplied via the feed device and feeding undosed liquid back in a return flow to enable it to be supplied again to the feed device. Also disclosed is a computer program product that includes code for a computer for implementing the disclosed method.