Frequently asked DPF questions

Diesel engines are efficient, but they create sooty particulates in their exhaust that are bad for health. Your Diesel Particulate Filter (DPF) removes them by pushing exhaust gases through a maze of fine channels that trap the soot.

The engine management system is meant to regenerate the filter when needed, by heating it to burn off the collected soot. For various reasons this can fail – one of the most common is a vehicle only used for short journeys, so it never gets fully up to temperature. When the filter becomes clogged, exhaust flow is blocked and eventually the engine management will apply a partial shut-down.

The filter is a sealed unit and expensive to replace – but with the right tools and techniques it can be cleaned.

A DPF warning light means soot is blocking the filter and the engine hasn’t been able to clear it on its own. By the time the light comes on, the blockage is already serious – so don’t wait for limp mode. Call us on 0333 366 1404 and we’ll advise on the right next step.

If you have an engine management light on, the problem needs to be fixed – even if the light goes off from time to time. It means the engine isn’t working properly.

Engine management systems will often put the vehicle into limp mode (“limp-home” mode) once the fault is detected, and it usually stays that way until the fault is cleared. You may be able to get home, but until it’s fixed the vehicle isn’t really usable – and ignoring it can lead to the vehicle stopping altogether, which is harder and costlier to fix.

Many garages will simply replace the DPF, but that’s expensive and often unnecessary: in most cases it can be cleaned on the vehicle at much lower cost.

Yes. As long as the vehicle starts and runs, we can usually clean the DPF on the vehicle. If it won’t start, our off-car factory cleaning service is the answer.

Yes, you do need it. Some garages will offer to cut the DPF out, but while it isn’t illegal for them to do it, it is 100% illegal for you to drive the vehicle afterwards – and if caught you can be fined upwards of £2,000. Your vehicle will also fail its MOT if the DPF is missing or not working properly, and it will have little resale value.

DPFs are a legal requirement for good reason: they remove diesel soot from the exhaust, and modern engines with DPFs have brought about a real improvement in air quality, particularly in cities.

We provide a full deep-cleaning service for diesel and petrol particulate filters (DPFs and GPFs), aiming to remove 95–98% of the filter’s contents:

• Pre-clean health check: our engineer reads the live data from your vehicle’s ECU to see how full the filter is, and checks the sensors, glow plugs and other components involved, to make sure the fault isn’t being caused by something else.
• Deep clean of the DPF: using our own in-house cleaning solution – the clean itself takes around an hour.
• Post-clean health check: we review the live data again to confirm the DPF has been cleared, reset the warning lights and check for any other fault codes. Where possible we do a short road test to confirm full power is restored.
• Your reports: copies of both health checks are emailed to you for your records.
• 30-day aftercare warranty on the cleaning work.

The clean itself takes around an hour. Allowing for the diagnostic checks before and after, most visits take about 90 minutes – longer if the DPF is very heavily blocked.

Regeneration means heating the DPF to around 600°C to burn off the soot inside. It happens automatically when the engine management system senses a build-up. A mechanic can also force it, but that carries a risk of cracking or damaging the DPF. If the engine’s own regeneration has failed to clear the blockage, a forced regeneration rarely works without proper cleaning as well. Read more here.

Garages often try to burn the soot off with a forced regeneration, but that doesn’t clear severe blockages. We specialise in DPF cleaning and can remove even the most stubborn blockages, using a cleaning solution we manufacture ourselves.

Yes. After the clean, the engineer resets the relevant warning lights.

Not usually. A blocked DPF can almost always be cleaned – clean where suitable, replace only where necessary. If the DPF is physically damaged it will need replacing, and we’ll tell you.

We deal with the DPF and the faults and blockages related to it, and reset the dash lights. A blocked DPF often has an underlying cause – such as sensor, EGR, injector, turbo or thermostat faults – and our engineer will advise you on anything else that needs fixing.

We always run a full diagnostic health check first to make sure the clean can be done. If the vehicle won’t start or run properly, there are other faults that need fixing first – or the DPF can be removed and sent to us for off-car factory cleaning. If the DPF is physically damaged, it will need replacing.