AdBlue Empty: Why the Diesel Won't Start

What AdBlue does

Newer diesel vehicles with SCR exhaust treatment inject AdBlue into the exhaust stream to reduce nitrogen oxides. If the AdBlue tank is empty, the vehicle can no longer meet emissions limits. That's why the electronics intervene.

The warning stages

The exact order varies a bit by manufacturer, but it usually goes like this:

1. First warning: a light or message in the dashboard; the tank still has enough left.
2. Second warning: the tank is nearly empty, the display shows a remaining range.
3. Third warning: the tank is empty, engine power may be reduced.
4. Start-lock: if the engine is switched off at zero kilometres remaining range, it often won't restart, even with diesel still in the tank.

Topping up: is that enough?

Whether topping up clears the start-lock depends on the vehicle. Some models only recognise the new level after some time, others need an additional reset by a garage if the lock was already active. A faulty level sensor can also mean the vehicle doesn't detect the level no matter how much you add. Read the owner's manual: it states how much you may add and how long the system needs to recognise it.

When you should call for help

• The engine doesn't start after topping up
• The warning stays even though the tank is full
• You're somewhere you can't top up, for example on the motorway, see Breaking down on the motorway
• The engine starts but runs roughly or loses power

The vehicle is then taken to a garage on a flatbed. What else to check on a diesel that won't start is in Car won't start. Important: if you've accidentally put AdBlue in the diesel tank, or diesel in the AdBlue tank, don't start the engine, see Wrong fuel.

Details for the towing service

• Make, model, year, diesel with AdBlue
• Which warning messages appeared and what the remaining range showed
• Whether you topped up, and how much
• Where the vehicle is