AdBlue (DEF) warning

The exhaust fluid that neutralises nitrogen oxides in a modern diesel is running low, or the system that doses it has reported a fault. Emissions rules require the car to restrict itself if the fluid runs out — usually reduced power first, then a refusal to restart.

• The fluid tank is low
• The wrong fluid, or contaminated fluid, has been added
• Crystallised deposits around the dosing injector
• Fluid frozen in very cold weather
• A level sensor or pump fault

Note the remaining distance the car displays and top up well before it reaches zero — once the countdown expires, the car may not restart, wherever it happens to be parked.

Use only fluid meeting ISO 22241, sold as AdBlue or DEF. Do not substitute anything else, and do not add water: the concentration matters and the system will detect it.

If the warning stays on after a correct refill, or the countdown keeps falling — that points at the dosing system rather than the level.