Why Does My Dash Say Service Def System? This is a question we get a lot and many things can cause this and we will go over some of the reasons this message comes up on your dash. Another question we get is Why Does My Truck Have A DEF System? We will look at both questions and give you some answers of why Diesel Trucks have a DEF System and why the Service DEF System message comes up on the dash. We will look at Why Does My Truck Have A DEF System first. The main reason late model Diesel Trucks and Cars have a DEF System is to control the amount of Nitrogen Oxides (NOx) that the vehicle emits. The EPA has mandated that the OEM’s had to control the Emissions that the Diesel Engine emits. The DEF Fluid gets injected into the exhaust stream before the Selective Catalytic Reduction (SCR) unit. The Def Fluid goes through a mixing tube and enters the SCR unit, and the DEF Fluid reacts with the SCR and reduces the NOx and lowers the emissions coming out of the tailpipe.
When the Service DEF System pops up on the dash with the warning that you have a certain mileage before the vehicle goes into Derate the cause can be as simple as bad DEF Fluid or a computer that needs reprogrammed to the latest software. When this message pops up we recommend that you bring the vehicle as soon as possible if you keep driving it will go into a 5mph Derate at that point the vehicle will need to be towed. There is a diagnostic process you must follow to fix these problems correctly. It starts with using a scan tool to check codes and checking for a computer reflash depending on the codes in the ECM is where you start the process. this message can be caused by bad DEF Fluid, NOx sensors, DEF Heaters, DEF Injector or the SCR unit failing. If your Diesel Vehicle is putting this message up on your dash give us a call and we would be happy to get it fixed for you and get your vehicle out of the Derate and running properly.