I am considering turning off the DEF system in my car, because it may leave me stranded one day as punishment and I haven't found a tuner yet to only make it work without forcing you to, it seems they can only turn it off completely. I would probably use it 90% of the time as designed, if I had the choice.

I read the claim that DEF reduces NOX emissions by 90%. On the other hand, people tell me that the benefit from DEF is not really clear yet. Cars are not the only source of NOX and maybe not even the major one. These bad gases may also liquify and disappear on their own within seconds.

Still I wonder, if I would significantly impact my own and others health when parking indoors for example.

My car is Euro 6 level, not sure how it would compare to other cars with adblue off.

Sources: enter image description here https://www.capitalremanexchange.com/20-facts-you-need-to-know-about-diesel-exhaust-fluid-def/#:~:text=DEF%20technology%20has%20been%20used,NOx%20by%2070%25%2D95%25.

Real emissions (dark cloud) not 90% less Euro 3 vs. Euro 6: enter image description here https://vcoe.at/service/fragen-und-antworten/was-sind-stickoxide-und-wie-schaedlich-sind-sie

What should I do? Will I start noticing adverse health effects, even if it's just watery eyes when standing behind my running car?

Will the exhaust gas somehow enter the cab while driving, causing long term health damage?

I am not worried about long term environmental effects because in 20 years there will be hardly any non-EV cars produced anywhere (probably).

  • Will the exhaust gas somehow enter the cab while driving, causing long term health damage? You'll get loads from the vehicle in front. And when standing behind my running car you should switch off the engine if you are not in the car. Commented Mar 10 at 22:21

1 Answer 1


There's a certain amount of wishful thinking and outright misinformation about NOX emissions that 'people' spread. Although there's more scientific work to be done there's ample evidence that NOX emissions are harmful to health and the environment, and the available data is convincing enough that regulators in the EU put limits on emissions. Regulators do not institute measures which increase the costs to own and run a car without compelling evidence.

As for how much DEF reduces NOX, 90% is a bit optimistic, a more realistic number is 80%, so turning your system off means you'll emit 5 times more NOX into the environment.

As for how harmful your car is to you, it isn't by itself, it's the collective emissions of all the other cars around you which your car contributes which is harmful. If you turn your DEF system off you are contributing that little bit more to everyone's lungs, including yours.

I'm not with Greenpeace, but I do have lungs and I for one would prefer you to keep your DEF system on.

  • I really wish I could selectively deactivate it to prevent getting stranded somewhere. But I talked to several tuners, only one said he could do it, but at insane cost. Still undecided. What about the graphic saying real NOX isn't really reduced that much Euro3 to Euro6? Assuming Euro3 had no DEF while Euro6 has. Commented Mar 13 at 15:17

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