AdBlue or Diesel Exhaust Fluid (DEF)

AdBlue or Diesel Exhaust Fluid (DEF) Issues

‘Check DEF’ Message

When the dreaded “Check DEF” message appears on the instrument panel of your Sprinter van, you need not panic. The AdBlue DEF system has to do with your  Sprinter’s emissions and it does not affect the performance of the engine. The “Check DEF” message means that either there is a level sensor fault inside the DEF tank or the DEF computer has detected a fault with one of the injectors or tank heaters.  However, if you ignore the DEF issue, you will get a warning that there will be 20 engine starts left and it begins a countdown each time the engine is started.

What is AdBlue?

AdBlue is a harmless substance. It is not a fuel, nor a fuel additive but a high-purity urea solution that must be used in a dedicated tank on your Sprinter van, that should be refilled before running low.  AdBlue is non-flammable and non-explosive. It is classified as a transportable fluid with minimal risk. The purpose of Adblue is to reduce the amount of harmful Nitrogen Oxide (NOx) found in your Sprinter’s emissions by turning it into nitrogen, carbon dioxide and water.  Mercedes-Benz has managed to significantly reduce exhaust gas emissions while at the same time maintaining the performance of diesel engines in terms of power and torque output. However, the Sprinter DEF system is complex and expensive.

The Sprinter Van DEF System

Mercedes designed a system by which the fumes pass through an Exhaust Gas Recirculation (EGR) valve before they enter the exhaust system. The exhaust system is made up of a CDI (control unit) which monitors and activates the sensors and valves in the exhaust system.  In the engine compartment of your Sprinter Van, there is a DEF tank, a DEF temp sensor, a DEF level sensor and a Selective Catalytic Reduction (SCR) control unit with actuators and sensors.  The actual exhaust system has three major components: the OXI-Cat and DPF section and two SCR Cat sections. The OXI-Cat section has an oxygen sensor an exhaust temperature sensor and a backpressure sensor. There is an N0x sensor and a dosing valve between the OXI-Cat section and the first SCR Cat section. In the first SCR Cat section, there is another temperature sensor, and the last SCR section has one more N0x sensor. Once the exhausted fumes and particles have passed through this area, they are passed through a particulate filter.

How We Can Help

As you can see, the system is quite complex and if any of these parts fail, you may not be able to use your Sprinter van.   What’s more, if you decide to take your Sprinter to a local dealership, you can expect high repair bills, both for parts and labour.  Here at Norlang Auto, our factory trained technician have the experience, knowledge and proper equipment to accurately diagnose and test this complex system.  Best of all, our repair bills will only be a fraction of the cost of what you’d normally pay at a dealership.  Our technicians are also able to reset the warning countdown before you are prevented from starting up the engine.  An important reminder for all owners of vehicles with the AdBlue DEF system is to avoid allowing the liquid to reach low levels since it can cause the pump and heater to fail and prevent you from starting your vehicle.  For more information about this vital system, please visit or call us at Norlang Auto.

Call us today to schedule an appointment and experience what we can do for you!