Those of you who belong to the dark side may be interested in this news item I saw on http://www.longlife.co.uk/ (I have no interest in diesels but was mulling over quad tail pipes at the time). May be old news of course.

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Decatting a Diesel

You CAN remove the catalytic converter on your Diesel Car without having a problem with the MOT. Having taken advice from VOSA, who control MOT testing in the UK, we are 100% confident that removing the CAT on a Diesel won't cause an issue. The confusion has arisen due to the regulations changing in January 2012 for cars which qualify for a full gas emissions test where 'if a cat was fitted as standard, it must be there for the MOT'. As Diesel cars don't qualify for a full gas emissions test, the regulation doesn't apply. The same is true for DPFs which you can also remove (they're not even mentioned in the manual)

Anyone can download the MOT testers manual HERE (http://www.motinfo.gov.uk/htdocs/index.htm) (you'll want the one for Class 3, 4, 5 and 7) and have a look. The part that deals with exhausts is Part 7.1 on page 157 (yes we've looked at this a lot!)

Obviously things can change but two inspectors from VOSA have both given the same information and said that nothing is going to change in the near future. If things do change then we'll be the first to let you know.

Information correct as of April 2012

Edited 2 June, 201214 yr by TsvRS

Thanks for posting that, it confirms my understanding of the situation too.

ISTR the early versions of the proposed 2012 MOT testers manual did actually state that any car originally fitted with a catalyst had to have one for the test. It was only later that this requirement was quietly moved to the spark ignition section of the manual, thus completely excluding diesels from it.

I don't think there was ever any intention by VOSA to include DPFs, but people began to speculate that if the MOT was to include diesel cats then it must be logical for them to include DPFs too. This rumour just snowballed from there, despite there being no truth in it at all from what I could gather.

The only thing you need to bear in mind is it has to pass the smoke test if the DPF is removed.

I put mine through its MOT at a main dealer and they correctly identified (and noted on the paperwork) that the DPF was absent and therefore smoke tested it. It passed easily.