Mercedes AdBlue fault repairs

Most Mercedes diesels badged BlueTEC or with a "d" on the boot — the C220d, E220d, GLC, Vito and Sprinter among them — clean their exhaust with AdBlue, a urea solution injected into the exhaust to cut nitrogen oxide emissions. When any part of that system fails, the car warns you and then counts down the miles until it will refuse to restart. That countdown is a legal requirement, so there is no safe way to ignore it.

The most common failures are well known: the heater in the AdBlue tank (needed to stop the fluid freezing), the AdBlue pump, the NOx sensors either side of the catalyst, and the dosing injector, which can block with crystallised AdBlue. On many models the heater and pump are built into the tank assembly, which is why a "simple" AdBlue fault can sometimes mean replacing more than people expect.

Topping up the tank is the first thing to try, but if the warning stays on after a top-up, or reads something like "AdBlue: No start in 500 miles", there is a fault that needs finding. We regularly see Sprinters and Vitos from local trades around Northfield and Longbridge with this warning — for a working van, a no-start is the last thing you need.

We read the fault memory, check the heater circuit, pump pressure and NOx sensor readings, and inspect the injector for crystals. Sometimes cleaning a blocked injector or replacing a single sensor is the whole fix. Where a tank module is needed we explain why and quote clearly. Removing or disabling the system is illegal and will fail the MOT, so we never do it.