DPF, EGR and AdBlue: what do they do and when do they fail?

The particulate filter, EGR valve and AdBlue system are the three components diesel drivers have the most trouble with. This article explains what they do, why they get stuck, and what your options are when things go wrong.

The particulate filter (DPF)

A diesel engine produces soot particles. The particulate filter traps them in a ceramic structure. Because that filter fills up, the car periodically burns it clean: regeneration. That requires the exhaust temperature to be high enough, which only happens if you drive for a while at a steady pace.

That's exactly where the problem lies. If you mostly drive short trips, regeneration never completes. The filter keeps filling up, the car tries more often, and at some point it goes into limp mode. Classic case: a diesel used mainly for a ten-kilometer commute.

What helps: a forced regeneration, cleaning the filter, or replacement if the ash loading is too high. And after that, a driving pattern that allows regeneration, otherwise you're back here in a year.

The EGR valve

The EGR valve routes part of the exhaust gases back to the intake. That lowers the combustion temperature and with it the nitrogen oxide emissions. The downside: those exhaust gases contain soot, and that soot settles in the intake manifold along with oil mist.

After a couple hundred thousand kilometers, that buildup can get thick enough that the valve no longer closes or opens properly. Result: power loss, a rough idle and a check engine light.

What helps: cleaning or replacing the valve, and cleaning the intake manifold along with it. That last step often gets skipped, so the new valve ends up sitting in the same mess.

The AdBlue system (SCR)

AdBlue is a urea solution injected into the exhaust. In the SCR catalytic converter that converts nitrogen oxides into nitrogen and water vapor. The system has a tank, a pump, a dosing injector, heating for winter, and NOx sensors that check whether it's working.

That's a lot of parts that can fail. The usual suspects: a crystallizing dosing injector, a faulty NOx sensor, and a tank heater that gives out. An annoying detail is that the car refuses to start after a number of warnings.

The fault codes you'll run into most often

Note: manufacturers also use their own codes that a generic scanner can't read.

What about disabling it in software?

We get that question a lot, so we're upfront about it. Disabling the particulate filter, EGR or AdBlue makes a vehicle no longer compliant with the requirements for public roads in the Netherlands and the rest of the EU. Since 2022 the APK's particle count measurement reliably shows whether the particulate filter is doing its job.

We therefore only offer this for export and for use on closed terrain, for example for vehicles heading to countries with different regulations. For a car that stays registered in the Netherlands, repairing it is the only viable route. We'd rather tell you that straight than have you come back to us with a failed APK.

Questions about a fault or error code on your car? Call us, or check out our ECU tuning and software range. Also read what tuning means for your warranty, insurance and APK.