A guide to DPFs – helping you to understand, and understanding how we can help
The Diesel Particulate Filter – commonly known as the DPF – has caused no end of problems for motorists since it was introduced.
It lowers emissions and makes our environment more pleasant by removing soot, and it is now illegal to either remove the DPF or disable it in any way. Since 2015 it has also been included in the MOT – we have to check that it is both fitted and working.
DPFs should regenerate through normal driving, generally requiring a speed of around 60mph for 20 minutes. (Check your vehicle manual for precise specifications.) If you’re unlikely to make this kind of journey then a modern diesel vehicle isn’t really for you, and could be the reason for any issues.
Blocked DPFs are a major problem and, with a new one often costing more than £1,500, no wonder every driver quakes if the warning light comes on. Your vehicle may also go into ‘limp home mode’ – limited to 2,000 revs and developing other engine management faults.
Your first act should be to seek help from a qualified expert to ensure the DPF is not damaged further, as prolonged blockage may result in permanent damage.
The DPF becomes blocked when regeneration has not occurred. There are a number of causes, so the fault needs to be identified before a chemical clean can be carried out or a ‘forced’ regeneration is electronically induced. If the original reason for failure is not established, the filter will simply become blocked again very quickly.
Common reasons for a vehicle not regenerating include:
Incorrect driving cycle
Glow plugs failing
Incorrect engine oil specification or infrequent oil changes
Blocked air filter
Pressure sensor failing
Lastly, the DPF itself could be worn out – but this is rare, so don’t panic straight away.
The repair process starts with a code-read, which will help us identify how the fault started. This is followed by a chemical clean. In the less likely event a 'forced regeneration is required an oil and filter change will then be needed, as the oil will become diluted by fuel.
After regeneration, it is essential the underlying fault is dealt with to prevent recurrence; if this is unclear, the driving cycle itself could be causing the problem i.e. excessively short journeys.
After resolving any problems with your DPF it is advisable to use an additional product in your fuel for a while that will reduce the burning point of the soot to enable easier regeneration.
We stock a high-quality product of this kind here at Carmaster, and we also welcome calls at any time to give advice on DPF issues and discuss a pricing structure. (Please note an accurate estimate for full repairs is unlikely without first carrying out an initial diagnosis and/or code-read.)