AdBlue-Füllstandsensor defekt

The sensor reporting how much reductant is in the tank, as distinct from the tank actually being low. The distinction is expensive to get wrong in one direction: a sensor believed over a genuinely empty tank ends with a vehicle that will not restart, and legislation makes that outcome final rather than negotiable.

Its readings are unusually hard to trust because the fluid is unusually hard to measure. Reductant crystallises on anything it dries against, including the sensor, and freezes below about minus eleven degrees. A sensor reading oddly in cold weather may be reporting frozen fluid correctly, which is a condition and not a fault, and the system is designed to thaw the tank before dosing.

Verify against the tank rather than against expectation. Add a measured quantity and watch the reading track it; a value that does not move, or moves in steps that do not match, is the sensor. Many of these are combined level, temperature and quality units, so a single failure produces several unrelated-looking codes at once — a cluster naming level, quality and temperature together usually means one part, not three.