FAQs

Q?

Can I ignore a DPF warning light?

A.

If you do find that your car is feeling far more sluggish than normal and/or there is a DPF warning light on the dash – DO NOT IGNORE IT. Driving the vehicle with a blocked DPF can seriously damage your engine / turbo and it’s not uncommon to have to replace a turbo when the warning light has been ignored for extended periods.

The ash residue which remains after successful regeneration cannot be removed and will eventually fill the filter. DPFs are designed to last in excess of 100,000 miles but, if the vehicle is operated correctly, many will far exceed this mileage.

Q?

What can prevent normal regeneration taking place?

A.

Frequent short journeys where the engine does not reach normal operating temperature.
Wrong oil type - DPF equipped cars require low ash, low sulphur engine oils.

A problem with the inlet, fuel or Exhaust Gas Recirculation (EGR) system causing incomplete combustion will increase soot loading.

A warning light on or diagnostic trouble code logged in the engine management system may prevent active or catalyst regeneration.

Low fuel level will prevent active regeneration taking place. As a general rule ¼ tank is required.

Oil counter/service interval - exceeding the service interval may prevent regeneration.

Q?

How long does a parked regeneration take?

A.

This process does not pertain to light-duty pickups and vans with 2007-compliant diesel engines. However, most medium-duty trucks are equipped with dash indicators alerting driver of the need for parked regeneration (also known as manual regeneration). The process takes approximately 20-40 minutes to complete.

Q?

How does my DPF Filter work?

A.

As with any filter, they ‘filter’ or trap particles, in this case harmful diesel exhaust soot particles, so they have to be emptied regularly to maintain performance. The DPF needs to be cleaned regularly, through a process called regeneration, either active, passive or forced regeneration, the accumulated soot is burnt off at high temperature (around 600°c) to leave only a residue of ash, effectively renewing or regenerating the filter, ready to take on more pollution from the engine.

Q?

What does DPF stand for?

A.

Diesel Particulate Filter

Q?

Why does the garage want to connect diagnostics equipment to check for DPF issue?

A.

Connecting diagnostic equipment to the vehicle will retrieve diagnostic trouble codes, which are used to locate the area of the engine requiring investigation.

Q?

How often should I check my DPF filter?

A.

Depending on driving style, regeneration takes places every 300 to 500 miles, when the DPF is filled with soot to a level of about 45-50% of its capacity.

Q?

What is regeneration?

A.

Regeneration is a process to clear the soot that has been collected inside the DPF.

Q?

Are vehicle manufacturers required to reduce emissions?

A.

Vehicle manufacturers are required to reduce diesel engine emissions in accordance with the Euro Emission standards. In order to achieve this reduced level of PM (soot), diesel particulate filters are now fitted to diesel engine vehicles.

Q?

Whats happens if I don’t maintain my DPF?

A.

Failure to correctly maintain your DPF by such methods as regeneration can cause diesel particulate filter issues: they become blocked, which increases exhaust emissions, stifles engine performance and sometimes even puts the car into a restricted ‘limp-home mode’.

Q?

How can I maintain my DPF?

A.

The best way to maintain a DPF is to make sure it’s fully able to regenerate itself when it’s full of soot (when the warning light appears).

There are two types of regeneration: passive and active.

Passive regeneration occurs when the car is running at speed on long motorway journeys which allows the exhaust temperature to increase to a higher level and cleanly burn off the excess soot in the filter. So it is advised that drivers regularly give their diesel vehicle a good 30 to 50 minute run at sustained speed on a motorway or A-road to help clear the filter. However, not all drivers do this type of driving regularly – which is why manufacturers have designed an alternative form of regeneration.

Active regeneration means extra fuel is injected automatically, as part of the vehicle's ECU, when a filter reaches a predetermined limit (normally about 45%) to raise the temperature of the exhaust and burn off the stored soot. Problems can occur, however, if the journey is too short, as the regeneration process may not complete fully. If this is the case the warning light will continue to show the filter is still partially blocked. In which case it should be possible to complete a regeneration cycle and clear the warning light by driving for 10 minutes or so at speeds greater than 40mph.

You will know whether active regeneration is taking place by the following symptoms:

Engine note change
Cooling fans running
A slight increase in fuel consumption
Increased idle speed
Deactivation of automatic Stop/Start
A hot, acrid smell from the exhaust

Q?

How long have vehicles had diesel particulate filters (DPF)?

A.

Diesel particulate filters have been fitted to diesel-fuel cars for almost two decades now - but if not maintained, or if tampered with there could be serious consequences for your car.

Q?

What is a diesel particulate filter?

A.

A diesel particulate filter (DPF) is a filter that captures and stores exhaust soot (some refer to them as soot traps) in order to reduce emissions from diesel cars. But because they only have a finite capacity, this trapped soot periodically has to be emptied or 'burned off' to regenerate the DPF.

This regeneration process cleanly burns off the excess soot deposited in the filter, reducing the harmful exhaust emission and helps to prevent the tell-tale black smoke you used to see from diesel vehicles, particularly when accelerating.

Euro 5 exhaust emissions legislation introduced in 2009 to help lower car CO2 emissions effectively made DPFs mandatory, and since then, around one in two new cars a year have been diesel-powered.

Q?

Is it illegal to remove a diesel particulate filter?

A.

Yes, it is illegal. Owners face fines if caught (up to £1,000 for cars and £2,500 for vans) and removing a DPF can also invalidate your car insurance policy.

Q?

What does the DPF warning light look like?

A.

If the DPF is becoming clogged with soot or a fault develops in the system, an orange light will typically appear on the dashboard as seen below.

Q?

Should I call for recovery if my diesel particulate filter light is glowing?

A.

There is no need to call for recovery if your DPF warning light is glowing. This light can often be rectified by going on a long drive; if it fails to extinguish, take your car to a garage or call us directly. Remember, orange warning lights are advisory; it’s red warning lights that require immediate attention and usually demand you stop the car as soon as possible.

Q?

Will my car fail it’s MOT if the DPF filters haven’t been maintained?

A.

You are required to check for a presence of a DPF filter in your vehcile. If it is gone, so are your chances of an MOT pass. According to .GOV "Garages and testing will be required check for a diesel particulate filter (DPF) in the inspection of the exhaust system as part of the MOT test (or annual test for heavy vehciles) from February 2014. The vehcile will automatically fail the MOT if the filter had been fitted as standard but is not found to be present."

A diesel particulate filter check has been part of the MOT test since February 2014. If a filter has been removed, the car will fail its MOT.

Removing the DPF will sometimes cause the warning light to glow – and this itself is an MOT failure point: no dashboard warning lights should remain on during the test.