Short journeys and diesel particulate filters
Mostly short trips can stop a diesel particulate filter from clearing itself, which is a common reason for the warning light and reduced power.
Yes, regular short journeys are one of the main reasons a diesel particulate filter clogs. The filter needs sustained heat to burn off the soot it traps, and a quick run to the shops or school rarely gives the exhaust enough time to get hot enough.
If your diesel has a DPF warning light, a loss of power or a smell of hot exhaust, this article explains what is happening, what you can sensibly try and what a garage can do.
Why do short journeys block a diesel particulate filter?
A DPF traps soot from the exhaust. To stop it filling up, the engine computer occasionally runs a regeneration, raising exhaust temperature so the soot burns away. This needs the engine fully warm and a steady drive, and the exact conditions depend on the vehicle.
On short, stop-start trips the process may never complete or may be repeatedly interrupted when you switch off. Over weeks the soot builds up, the filter becomes restricted and the computer eventually shows a warning. Town driving and a lot of idling make the situation worse.
What are the signs of a clogged DPF?
A dashboard filter symbol is the usual first warning. Other signs may follow if it is ignored:
- DPF or engine management warning light
- Loss of power or limp mode
- Cooling fan running after the engine is switched off
- Rising fuel use
- A smell of hot exhaust or more idling revs than normal
Will a long drive clear my DPF?
Often it will, if the filter is only partly loaded. Your handbook describes what the manufacturer recommends, but a sustained drive on a road where you can hold a steady speed once the engine is fully warm is the typical approach. Do not do this if the car feels unsafe, and obey speed limits.
Be aware that a warning light on a car that has done a lot of short trips may mean the filter is already too blocked for a drive to clear. Repeated failed attempts, or ignoring the light, can lead to extra engine oil dilution and more expensive faults, so do not keep trying for weeks.
What will a garage do about a blocked diesel particulate filter?
A technician will read fault codes, check pressure and soot readings and look for related problems such as a faulty sensor, EGR fault or injector issue that stopped regeneration. Depending on the vehicle and the level of blockage, a forced regeneration or a professional clean may be possible. In other cases the filter needs replacing.
Cost drivers include the vehicle, the soot load, whether the cause lies elsewhere, the price of a filter and the time needed. We will not promise a result before diagnosis, but we will explain what we find. Automaster is a garage at Longcombe Cross near Totnes, and we welcome questions about diesel exhausts.
How do I stop my DPF blocking again?
Give the car a regular longer run when the engine is warm. If most of your driving is short, mention it when you ask us for advice. Using the correct engine oil for a DPF-equipped car matters too, so check your handbook.
Keep up with servicing and deal with warning lights early. A diesel that misses regenerations because of another fault will keep clogging until that fault is fixed. If limp mode appears or the car loses power in traffic, stop in a safe place and get advice rather than pressing on.
Short trips are hard on a DPF, and longer runs plus prompt attention to warnings can help. If yours is already complaining, ask Automaster for a quote or call the quote line.
Common questions
How long should I drive to clear a DPF?
It depends on the vehicle, so check your handbook. As a general rule the engine needs to be fully warm and held at steady speed for a sustained period, rather than a brief trip.
Can I remove my DPF?
We would not recommend it. Removing a particulate filter from a vehicle that was built with one can cause an MOT failure and legal problems.
Will a DPF cleaning additive fix it?
Some additives may help prevent a build-up, but they are not a cure for a heavily blocked filter. A scan and inspection will show how loaded it is.
Do petrol cars have particulate filters too?
Some newer petrol models do have them, but the advice in this article is aimed at diesels. Check your handbook if you are unsure what your car has.
More advice
Ask for a quote
Tell us the make, model, registration and what the car is doing, and we will come back to you. Prefer to talk? Call our quote line on 01803 862152.
Automaster, Longcombe Cross, Longcombe, Totnes TQ9 6PL, United Kingdom