Got an AdBlue Problem?
Understand the warning.
The definitive UK resource for AdBlue, DEF and SCR fault information. Find out what your warning light means, decode your fault code, and get the right help before your engine is immobilised.
Find AdBlue Information for Your Vehicle
Enter your UK registration to find relevant SCR faults and guides.
Check My AdBlue Fault
Enter a fault code or dashboard warning to find information about your AdBlue, DEF or SCR problem.
Select Your Vehicle Type
Emissions systems behave differently depending on the application. Choose your vehicle category for specific manufacturer guides.
What's Your Vehicle Doing?
Find explanations for common symptoms and dashboard warnings.
AdBlue Warning Light
Why your warning light is on and what to do.
Warning Still On After Refill
You topped up the tank, but the light remains.
Restart Countdown
Vehicle says "No Engine Start in X Miles".
Vehicle Won't Start
The countdown reached zero and the engine is immobilised.
Engine Derate / Limp Mode
Reduced power and torque due to emissions fault.
NOx Sensor Faults
Understanding NOx sensor failures.
AdBlue Pump Failure
Low pressure faults and delivery issues.
Injector Crystallisation
White crystal buildup blocking the exhaust injector.
How an AdBlue/SCR System Works
AdBlue (or Diesel Exhaust Fluid) is not a fuel additive. It is injected directly into the exhaust stream to reduce harmful Nitrogen Oxide (NOx) emissions into harmless nitrogen and water.
- 1
Engine Exhaust: Exhaust gas containing NOx leaves the engine and passes through the DOC/DPF.
- 2
Dosing Injector: The AdBlue pump pressurises fluid to the injector, which atomises it into the hot exhaust.
- 3
SCR Catalyst: The urea turns into ammonia and reacts with the NOx across the catalyst brick.
- 4
NOx Sensors: Sensors monitor the effectiveness. If efficiency is low, a warning is triggered.