AdBlue (DEF) injects urea into the exhaust to convert NOx into nitrogen and water. The system is delicate — and when it fails, modern diesels go into a strict 'No Engine Restart in X miles' countdown that ends with a car that won't start at all.
Top 3 AdBlue faults we see
1) NOx sensor failure — the most common cause, especially on VAG group and Mercedes diesels. 2) Blocked or failed AdBlue dosing module. 3) AdBlue heater failure, where the tank freezes in winter and the system can't dose at all.
How we diagnose properly
We don't just clear codes. We read live SCR system data — tank level, dosing quantity, temperature, NOx upstream and downstream readings — to confirm the actual failed component before replacing anything.
AdBlue delete — when it's appropriate
For off-road, motorsport and export vehicles we offer full AdBlue delete remapping. On a road-registered UK vehicle this is an MOT failure — we will only carry out AdBlue delete on vehicles that won't return to road use.
Repair vs delete
If you intend to keep your car on the road, the right answer is almost always a proper diagnosis and component replacement. We carry NOx sensors and dosing modules for most popular makes on the van.