Yes it is as is deleting Adblue. And the consequences are scary if your caught.
If you're caught deleting your vehicle's DPF (Diesel Particulate Filter) or AdBlue system, you face significant consequences, including
fines, a
failed MOT test, an
invalidated car insurance policy, and potential
vehicle warranty issues. It is illegal to remove these emission control systems, as they are essential for reducing harmful pollution, and doing so makes your vehicle non-compliant with emissions regulations, rendering it illegal for road use.