European Exhaust and Catalyst
European Exhaust and Catalyst
DPFs and the MOT
Published on: 10/01/2019

The MOT emissions testing will continue to become more stringent with regard to the level which is permitted to be emitted; this is a result of the continued pressure from governments to totally eliminate harmful emissions.  For example, Euro 6 diesel emissions systems require the exhaust gases to pass through 4 separate filters/catalysts e.g. Oxicat, DPF, Diffuser, and SCR (Selective Catalytic Reduction).

The DPFs that are currently fitted to the majority of diesel vehicles are basically just a porous filter for the collection and disposal of sooty particles or particulate matter (PM).

In perfect combustion conditions, carbon dioxide, water and nitrogen are the end products. In reality, the incomplete combustion of diesel fuel results in emissions that include oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide (CO2), water (H2O) and unburnt hydrocarbons (HC), as well as engine oils, debris, soot and ash particulates, all are known as particulate matter (PM).

This particulate matter (PM) can be categorised into two groups: Particles of 2.5 microns to 10 microns, and Particles of less than 2.5 microns in size.  

Although most Diesel Particulates are very small more than 99% are in the sub 2.5 microns range. All are damaging to your health, as they are carcinogenic.

Wall-flow diesel particulate filters usually remove 85% or more of the soot and can at times (in heavily loaded conditions) attain soot removal efficiencies close to 100%.

The DPF is a filter designed to collect PM, if extra PM is produced it will be the result of problems up stream of the DPF. Faulty components that can generate high levels of PM: fuel injectors, glow plugs, incorrect oil, contaminated oil, Turbo’s, EGR valves, air filter and a lack of regular maintenance. Some fuel additives such as EEC’s 6 in 1 will help to keep carbon deposits off all of these components as well as assisting the regeneration of the DPF.

If the DPF sign is illuminated check the engine oil for diesel contamination.  Failure to do so could result in an expensive repair bill for a new DPF or/and a new turbo.

It is extremely important to use the correct grade of engine oil as recommended by the manufacturers.

90% of turbo failure is oil related (data from BTN). Turbo failures will also result in a damaged DPF.

The DPF is designed to not only collect the PM (particulate matter), but also to clean its self, which is called regeneration: It will occur when the DPF reaches a pre-determined PM fill level (around 40%) the ECU will then activate the regeneration process which can inject up to 8 times the amount of fuel through the engine to produce temperatures in the DPF in excess of 550 degrees which will burn off the PM within the DPF.


DPF regeneration will not take place if:

  • An engine management light is on for any fault
  • There is less than 20 litres of fuel in the fuel tank or if the fuel light is on
  • The pressure sensors have a build-up of carbon

You must:

  • Examine pressure pipes for damage, they must be clean and dry.
  • Check that the EGR system is working correctly.
  • Check that the vehicle has the correct spec engine oil.
  • Check the engine oil for diesel contamination (this could be the result of regeneration).
  • Check the fuel additive (active system) Eolys

If DPF is not regenerated and fills to over 90% or 45 grams of PM, the DPF may need replacing. Blocked DPF’s are not covered under warranty.

When fitting a new DPF the ECU must be reset and then a forced regeneration carried out, this is to ensure that the ECU knows that the DPF and all related sensors are reset.

DPFs are now part of the MOT. If they have been tampered with in any way it will result in an MOT failure.

DPF removals can result in an invalid motor insurance claim: Re: Road Vehicles (Construction & Use) Regulations (Regulation 61a(3).


Data & Procedures May Vary Between Manufacturers

EEC has an extensive range of DPFs which is increasing day by day.

EEC is committed to an education and training programme within the industry to help technicians understand, evaluate and diagnose emission problems.                                                            

EEC has invested heavily in our own wash coating facility in Denmead, this is to ensure we produce a top quality product for our home and export markets.     

For information regarding emissions, DPF, 4 gas analyses, and technical training, please contact Duncan Richards or Stuart Still –