Abstract: A fill level detection apparatus (23) is introduced for ascertaining a fill level in a storage tank (19) for a liquid reducing agent for use in an exhaust gas aftertreatment device (3), having a fill level detector (21) and a driving and evaluating unit (22), which are connected to each other with electrical lines (47a, 47b, 47c) and with respect to DC-currents are decoupled from each other by capacitors (45), which are connected in series with said electrical lines, and with respect to AC-currents are coupled with each other. Said fill level detection apparatus is thereby characterized in that the capacitors (45) are disposed as part of the fill level detector (21) separated from the driving and evaluating unit (22) by the electrical lines (47a, 47b, 47c).