As governments tighten the reins on vehicle emissions, MOT emissions testing is becoming increasingly rigorous. The push to reduce harmful pollutants means stricter limits on what can come out of your exhaust.
For example, modern Euro 6 diesel emissions systems require exhaust gases to journey through a series of four sophisticated filters and catalysts, including an Oxicat, DPF (Diesel Particulate Filter), Diffuser, and SCR (Selective Catalytic Reduction).
What Are DPFs and Why Do They Matter?
Diesel Particulate Filters (DPFs) are the unsung heroes of modern diesel engines, designed to trap and dispose of sooty particles—formally known as particulate matter (PM). Think of them as high-tech sieves, catching harmful particles before they can escape into the atmosphere.
Under ideal combustion conditions, a diesel engine would emit only carbon dioxide, water, and nitrogen. But real-world conditions are far from perfect. The incomplete combustion of diesel results in a cocktail of emissions: nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and particulate matter laden with soot, ash, and even traces of engine oil debris.
Understanding Particulate Matter (PM)
PM falls into two categories:
- Particles between 2.5 and 10 microns
- Sub-2.5 micron particles
Shockingly, over 99% of diesel particulates are smaller than 2.5 microns—tiny but incredibly dangerous. These particles are carcinogenic, posing severe health risks. Fortunately, wall-flow diesel particulate filters can capture at least 85% of these harmful particles, with some systems achieving nearly 100% efficiency under high-load conditions.
The Role of Maintenance in DPF Health
Your DPF is a marvel of engineering, but it’s not invincible. Excessive PM production usually points to upstream issues, such as:
- Faulty fuel injectors
- Malfunctioning glow plugs
- Contaminated or incorrect oil
- A clogged air filter
- Problems with turbos or EGR valves
Routine maintenance is key. Using high-quality fuel additives—like EEC’s 6-in-1—can prevent carbon buildup, protect components, and assist with DPF regeneration.
Signs of Trouble: What to Watch For
If your DPF warning light illuminates, don’t ignore it. Check your engine oil for diesel contamination immediately. Neglecting this issue could lead to costly repairs, including replacing your DPF or turbocharger. Keep in mind: 90% of turbo failures are linked to oil issues, and a failed turbo can damage your DPF.
How DPF Regeneration Works
DPFs don’t just trap PM—they also clean themselves through a process called regeneration. When PM levels reach about 60%, the engine control unit (ECU) initiates regeneration, injecting additional fuel to heat the DPF to over 550°C. This burns off the accumulated PM.
Regeneration won’t occur if:
- Poor engine maintenance.
- Turbo issues.
- Injector issues
- Faulty pressure sensors.
- Faulty temperature sensor.
- Faulty EGR valve.
- Damaged exhaust system (low/high back pressure Air leaks upstream of the DPF).
- Incorrect oil, Incorrect fuel
- There needs to be 20 litres + of diesel in the fuel tank, or regeneration will not take place.
- Engine oil levels can increase due to diesel getting into the engine, as a result of the regeneration process. If this accurse you need to replace the engine oil and oil filter, when replacing the DPF.
- Regeneration will not take place if the EML light on.
- Do not use sealant up stream of a cat or DPF
To ensure proper regeneration:
- Inspect pressure pipes for damage or debris.
- Verify the EGR system is functioning correctly.
- Use the manufacturer-recommended engine oil.
- Check for diesel contamination in the engine oil.
- Ensure the active system fuel additive (e.g., Eolys) is sufficient relating to PSA vehicles.
- Ensure the fuel vaporiser is working correctly ( Relating to some Ford Models)
If the DPF fills beyond 90% capacity (or 45 grams of PM), it may become irreparable. Blocked DPFs aren’t covered under warranty, so prevention is paramount.
DPFs and the Law: What You Need to Know
Tampering with your DPF is a big no-no. Under MOT regulations, a modified or removed DPF is an automatic fail. Worse yet, it could invalidate your motor insurance under the Road Vehicles (Construction & Use) Regulations [61a(3)].
EEC: Your Partner in Cleaner Emissions
At EEC, we’re committed to helping technicians tackle emission challenges. With a growing range of high-quality DPFs and an in-house wash-coating facility in Denmead, we prioritize excellence for both domestic and export markets. Our education and training programs empower industry professionals to diagnose and resolve emission issues with confidence.
For more information on emissions, DPF systems, 4-gas analysis, or technical training, contact us at [email protected].