Amber light
AdBlue / DEF Warning
The diesel exhaust fluid (AdBlue) level is low, or the emission system using it has a fault.
High risk
Top up AdBlue soon. If it runs out, many cars will not restart until it is refilled.
Short answer · What happens if AdBlue runs out?
Emission rules require that the car limits power or cannot be restarted once the tank is empty. The display usually counts down the remaining distance. Top up with AdBlue (ISO 22241) into the blue-capped filler; never put it into the fuel tank.
What to do
- Top up AdBlueUse AdBlue to ISO 22241 in the blue filler.AdBlue in the diesel tank causes expensive damage.
- Watch the countdownNote the remaining distance shown.
- Diagnose system faultsIf the warning stays on after filling, the SCR system needs a check.
How is the light behaving?
| What you see | What it usually means | What to do |
|---|---|---|
| Steady | AdBlue low | Top up soon |
| Flashing | Very low or system fault; restart may be blocked soon | Top up or have it checked now |
Possible causes
- Low AdBlue levelNormal consumption.
- Crystallised doser or lineDeposits block the flow.
- NOx or level sensor faultWrong readings trigger the warning.
- Poor-quality fluidContaminated fluid sets quality codes.
Don't confuse it with
Questions about AdBlue / DEF Warning
How much AdBlue does a car use?
Roughly a few percent of diesel consumption, depending on the engine.