Why is my AdBlue warning light on?
AdBlue warning light: causes, countdown and fixes
The short answer
AdBlue is a fluid injected into the exhaust of many modern diesels to cut nitrogen oxide (NOx) emissions, through a system called SCR. The warning can mean the tank is low, the fluid is poor quality, or a part of the system has failed. On most vehicles a persistent fault starts a countdown, after which the engine will not restart. So do not ignore it.
Common causes
- Low fluid level, sometimes much sooner than owners expect
- Crystallised or leaking AdBlue dosing injector
- Failed pump, tank heater or level sensor
- Faulty NOx sensor reporting the system is not working
- Contaminated fluid, or something other than AdBlue in the tank
What not to do
Do not fit an AdBlue “emulator” or have the system switched off. It makes the vehicle illegal to use on the road and is checked for at roadside and MOT inspections.
What to do now
- Top up with AdBlue to ISO 22241 from a sealed container, then drive as the handbook advises.
- If the warning stays or a countdown appears, book a diagnosis before the countdown runs out.
- Bring any fault codes and tell us what has already been replaced.
Draft Technical wording to be reviewed by PK before publishing.