Methods and systems are provided for estimation of a volume of liquid diesel exhaust fluid (DEF) contained within a DEF tank. In one example, a method for the estimation of the volume of liquid DEF in a DEF tank during DEF freezing conditions may include activating a heater contained within the DEF tank, and then switching estimation of the volume of liquid DEF via a first transfer function to estimation of the volume of liquid DEF via a second transfer function.