Does DPF removal cause MOT issues


Staff member
Deal, Kent UK
A3 1.4 TFSI 150 COD
Does removing a DPF have any impact on a cars emissions levels and will it affect the annual MOT test?

I know if I took off a Catalyst from a petrol engine the chances are it will fail the emissions test but do DPF's have the same effect as they just filter out the particles?

THE UK MOT RULES CHANGED IN FEB 2014, so some of the older posts in this thread may therefore be inaccurate. DPF REMOVAL is an instant failure if spotted by the tester.
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As far as I know there is no problem as the smoke test is visual only. So long as the car goes through on the fast-pass test it will not be revved hard enough to chuck out enough soot for the MoT tester to have any cause for concern.

This of course subjective. A difficult or ruthless examiner will fail it due to the absence of the DPF.

Slightly like exhaust mounts. Some tester will fail a car for one broken mounting. But AFAIK the test manual simply states that the exhaust must be mounted securely. Let's say the subject car being tested has one failed mount point but the other (let's say 9 - depends entirely upon the car in question) are still sound. Provided the exhaust system is secured to the car then in my opinion it's not cause to issue a fail notice.

I suppose it depends upon the general condition of the car (also very subjective and is down to the tester's opinion) too. If everything is in order then the tester will more likely take a sensible stance on such issues. If it's a general wreck then you're not gonna pass either way.
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Cause diesel are smoke density tested then on a newer car with stricter smoke levels to adhere to then I would say it is a possibility certainly, but if it passes the smoke test regardless then there shouldn't be a problem unless (like Paul says) the tester is just a jobsworth,

When I had my 306 with the 2.1 xud11 in it, I took it for an MOT just after they changed the rules regarding catalytic converters and dashboard warning lights, I fixed my intermittent air bag light (turned out to be the rotary switch behind the steering wheel) but I didn't put a cat back in the exhaust, I removed it way before the new rules came in,
when i took it for MOT though, the guy never checked the dashlights, and didn't even mention that I should have had a cat and just passed it, he just gave me an advisory for the handbrake being just about passable.....

So really it's just luck of the draw... theoretically a petrol could pass an MOT without a cat as long as the emissions are ok...
They are supposed to check for the presence of the DPF although there shouldnt be too much of an issue providing the engine is running well.

i see some removal companies are offering to remove the internals of the DPF so its just a straight through pipe but looks normal from the outside
Depends what sort of map you get. If you've got a V-Switch then I believe the maps can be chopped and changed as and when required
If a car leaves the factory with a dpf or cat fitted law states that it has to remain fitted to pass mot. But as above take out the internals of the dpf or cat and refit same goes for the mufflers( straight pipe with a can welded around it )

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