Not on a vehicle you use on the road. A vehicle that was built with a diesel particulate filter (DPF) fails its NCT without one: a DPF that was fitted when the vehicle was made but is now missing is a major fault1. “Deleting” it with a remap doesn’t change that, because the inspector checks the exhaust itself. “Just have it removed” is advice that still circulates when a DPF blocks, often from businesses that sell the service. Here is the position in Ireland, and why removal doesn’t fix the problem anyway.
The NCT checks for it
On a diesel, the NCT inspector checks that the emission control system fitted by the manufacturer is present, complete, properly connected and has not been bypassed1. These are major faults, so the vehicle fails1:
- a DPF, EGR valve or catalytic converter that was fitted when the vehicle was made but is now missing;
- an emission control system fitted by the manufacturer that is absent, incomplete, incorrectly assembled or obviously defective;
- leaks that would affect the emission measurements, and exhaust smoke likely to affect other road users.
The smoke test is strict too. A diesel first registered after 1 July 2008 fails if its average smoke reading is over 1.5 m-1, or over 0.7 m-1 if it was first registered after 1 September 2015 with a Euro 6 engine, and any diesel fails if its reading is over the figure on the manufacturer’s plate on the vehicle1.
A remap that stops the warning lights does not change any of this. A vehicle that fails gets no NCT certificate until it passes a re-test, which must be booked within 21 days and carried out within 30 days of the test, and the NCT is enforced by An Garda Síochána, who have access to NCT records2.
Roadworthiness and insurance
Motor insurance and road traffic legislation require you to keep your vehicle in a roadworthy condition at all times, whatever its NCT date2.
Insurers ask about modifications, and removing a DPF is one. Under the Consumer Insurance Contracts Act 2019 you must answer an insurer’s questions honestly and with reasonable care, and the same applies to the questions it asks at renewal3. If an answer was careless, the insurer’s remedy reflects what it would have done had it known the full facts: it can pay less on a claim, or, if it would not have insured the vehicle at all, cancel the policy and refuse all claims, returning the premiums. If an answer was fraudulent, it can cancel the policy3. And a vehicle without its DPF will fail its next NCT, whoever owns it by then1.
It doesn’t fix anything anyway
DPFs rarely block for no reason. The most common cause is soot building up faster than regeneration can burn it off, because of the way the vehicle is driven or a fault elsewhere: the EGR valve, sensors, pressure pipes, leaking injectors, glow plugs or the wrong engine oil4. Remove the filter and that fault is still there. The better path: find the cause with our guide to why DPFs block, fix it, and if the filter can’t be recovered, fit a type-approved replacement. See the DPF range, including Premium silicon-carbide DPFs with a 3-year warranty, and combined catalytic converter and DPF units.
Selling a non-approved DPF is an offence too
For a vehicle approved to Euro 5 or Euro 6, a replacement DPF must be type approved5, and in Ireland it is an offence for a business to make available on the market a component that is subject to approval without that approval6: see type approval and the law. In our range, every DPF and combined unit catalogued for a Euro 5 or Euro 6 vehicle is type approved. Find yours: Ford Transit DPFs, Opel Vivaro A DPFs, Mercedes Sprinter DPFs or all vehicles.
Sources
- Road Safety Authority, National Car Test (NCT) Manual 2023, version 5.1, sections 8.2.2.1 (exhaust emissions control equipment) and 8.2.2.2 (exhaust emissions, diesel). ncts.ie
- National Car Testing Service, Frequently Asked Questions: insurance and roadworthiness, test results, re-tests and enforcement. ncts.ie
- Consumer Insurance Contracts Act 2019 (No. 53 of 2019), sections 8, 9 and 14 (revised text). revisedacts.lawreform.ie
- BM Catalysts, “Diesel Particulate Filter Information & Fitting Advice”. bmcats.com
- Regulation (EC) No 715/2007, Article 11; Commission Regulation (EU) 2017/1151, Article 10. eur-lex.europa.eu
- European Union (Road Vehicles: Type-Approval and Market Surveillance) Regulations 2020 (S.I. No. 556 of 2020), regulation 17. irishstatutebook.ie