AdBlue and diesel: where to top up and what not to mix up

AdBlue is a fluid used by the exhaust after-treatment system on compatible diesel vehicles; it is not a fuel additive. Identify the correct filler using the vehicle handbook.

Find the correct filler

The AdBlue filler is separate from the diesel filler. Its location varies by model and may be beside the fuel cap, in the boot or under the bonnet. Do not rely on the cap colour: check the symbols and instructions in the vehicle handbook. If in doubt, ask an attendant or garage before opening a container.

AdBlue is a urea-based solution used in the selective catalytic reduction (SCR) systems of some diesel engines to control emissions. It is not fuel and must not be mixed with diesel. Putting it in the diesel tank, or diesel in the AdBlue tank, can cause damage and requires technical assistance. Do not start the engine if you think you have used the wrong filler. Contact assistance and explain exactly what was added.

Top up as the handbook instructs

Check whether the vehicle reports a low level and what product and procedure the manufacturer requires. Use a sealed, suitable container, avoid contaminating the fluid and follow the instructions for opening, quantity and cleaning. Do not overfill the tank or improvise mixtures or additives. Procedures vary by model; the handbook takes precedence over general advice.

After topping up, close the cap properly and wait as directed for the level to be detected. Some vehicles update the warning after driving or a particular restart procedure. If the warning remains, do not keep topping up blindly: check the handbook and contact a service centre.

Storage and safety

Store the product as stated on the label and in the handbook, avoiding contamination and unsuitable temperatures. If you spill it, clean it as the manufacturer directs and do not leave it on surfaces where it can crystallise. Keep the operation away from flames and hot parts, and keep the container out of children’s reach.

AdBlue goes in its dedicated filler, never in the diesel tank. If you accidentally put it in the fuel, do not start the engine: tell the attendant and call for assistance. If it spills on the bodywork, rinse it with water as directed on the product, as it can leave crystallised residue.

To study vehicle theory, Quiz Patente Ufficiale offers chapters, timed exam-style quizzes and error review; follow the vehicle-specific handbook for topping up.