DPF Warning Light On? What It Means and What to Do

What the DPF light means

The DPF (diesel particulate filter) warning light means the filter in your diesel's exhaust is getting clogged with soot and needs to clear itself. The filter traps soot from the exhaust and normally burns it off on its own during a process called regeneration. The light comes on when that has not been able to happen. In many cases a steady run at motorway or dual carriageway speed will clear it — check your handbook for the exact advice for your car.

Why it happens — short trips

Regeneration needs the exhaust to get very hot, which only happens after a sustained drive at a steady speed. If most of your journeys are short, stop-start trips around town, the filter fills with soot faster than it can burn it off. That is why DPF problems are so common on diesels used for school runs and local errands rather than long commutes.

Other causes include a faulty pressure sensor, an EGR valve fault, a problem with the injectors, or the wrong grade of engine oil — diesels with a DPF need a low-ash oil to the manufacturer's specification.

How to try to clear it yourself

When it is safe and legal to do so, drive for around 15 to 20 minutes at a steady speed on a faster road, keeping the revs up by staying in a lower gear than normal. From Northfield, a run out along the A38 towards the M5 or the M42 is the sort of drive that gives the filter the heat it needs. If the light goes out, the regeneration has worked.

If the light stays on, comes on alongside the engine management light, or the car goes into limp mode (reduced power), stop trying and get it looked at. Driving on with a blocked filter can lead to much more expensive damage.

Do not remove it

Removing or tampering with a DPF is illegal and is an MOT failure. Diesels fitted with a DPF also fail the MOT if they give off visible smoke of any colour during the test. If you are offered a DPF removal, the car will not be road legal and your insurance may be invalid.

What we do

We read the fault codes and check the soot level and pressure readings to find out why the filter is blocking, not just clear the light. Depending on what we find, that may be a forced regeneration using diagnostic equipment, a DPF clean, fixing the sensor or EGR fault that caused it, or replacing the filter if it is beyond cleaning. You get a clear explanation and a written quote before we start. Call us on 0121 476 2287.