AdBlue-Temperatursensor defekt

The sensor reporting the temperature of the AdBlue in the reductant system has failed.

Reductant is a urea solution injected into the exhaust to convert NOx, and its temperature is measured because it freezes at a temperature the car will routinely meet — about −11 °C. That is an ordinary winter night across most of Europe and North America.

The design accommodates freezing rather than preventing it. The tank is built so expanding ice does not damage it, and the vehicle is permitted to run without dosing while it thaws — so a delay before dosing begins on a cold morning is normal behaviour, not a fault. The system carries heaters, and this sensor is what decides when to use them and when dosing may safely resume.

Temperature matters for a second and less obvious reason: dosing quantity depends on the solution's concentration, and concentration is inferred from properties that vary with temperature. So a wrong reading produces a wrong dose rather than no dose — which is harder to detect and shows up as NOx conversion efficiency rather than as an obvious failure.

The consequence of leaving it is what makes this urgent. Emissions legislation requires the vehicle to enforce its own aftertreatment: a persistent reductant fault leads to reduced power and eventually a refusal to restart, on a mandated countdown the dashboard will state in miles. It is drivable now and it will not stay that way.