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DPF light on? What it means and what to do

The short answer

The DPF light means the diesel particulate filter in your exhaust is getting clogged with soot and needs to burn it off. If it's a steady light on its own, a longer steady drive at motorway speed will often let the filter clean itself and clear the light. If the light is flashing, other warnings have joined it, or the car has dropped into limp mode, stop driving hard and get it checked before the blockage gets worse.

The DPF is a filter that traps the soot from a diesel engine so it doesn't come out of the exhaust. Every so often the car burns that soot off in a process called regeneration. The warning light is the car telling you the soot has built up and a regen either needs to happen or has failed to finish.

Exhaust tailpipes on the back of a car

Common causes and what they mean

A few things could be behind it. Here's what each usually points to, and how serious it is.

Too many short journeys

Lots of short, stop-start trips never let the exhaust get hot enough to regenerate. The soot builds up with nothing burning it off, which is the most common reason the light comes on.

Interrupted regeneration

If you switch the engine off partway through a regen, or never drive far enough for one to finish, the cycle never completes and the filter stays full.

Sensor fault

The car works out how blocked the filter is from pressure and temperature sensors. A faulty sensor can trigger the light or stop a regen starting even when the filter is fine.

EGR valve problem

A sticking or clogged EGR valve upsets the engine and makes it produce more soot than normal, which loads the DPF up faster. A diagnostic check tells us if that's what's going on.

A genuinely blocked filter

If the light has been ignored for a while the filter can clog to the point it won't regenerate on a drive at all, and it needs a forced regen or a proper clean.

Can I still drive with the DPF light on?

A steady DPF light on its own is usually the car asking for a longer run, so a 20 to 30 minute drive at a steady 50 to 60mph in a lower gear will often trigger a regen and clear it. If that doesn't clear it, or the light is flashing, or other warning lights come on, or the car goes into limp mode with the power cut back, stop driving it hard and get it checked. Carrying on with a badly blocked filter can force a garage regen or a new DPF, which is a far bigger bill than sorting it early.

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DPF light FAQs

Often, yes, if you catch it early. A steady 20 to 30 minute run at 50 to 60mph in a lower gear keeps the exhaust hot enough for the filter to burn off the soot and complete a regen. If the light stays on after a good long drive, or keeps coming back, the filter or a sensor needs looking at properly.

The filter keeps filling with soot until it's too blocked to clean itself on a drive. At that point the car often drops into limp mode to protect itself, and you need a forced regeneration or a full DPF clean. Left long enough the filter can be damaged beyond cleaning and need replacing, which is expensive, so it's much cheaper to deal with it early.

We come to your driveway or work and plug in to read exactly what the car is reporting, so you know why the light is on and whether it's the filter or a sensor. The DPF clean or forced regen itself isn't a job we take on, so if that's what it needs we'll tell you straight and point you the right way rather than have a go at it. If the fault turns out to be something we do cover, we can sort it at your door across Soham, Ely, Newmarket and Cambridgeshire.

Usually it's the type of driving. If the car mostly does short, cold, stop-start trips it never gets hot enough to regenerate, so the soot builds up again and again. It can also be an EGR fault making extra soot, or a sensor that isn't letting a regen run. Reading the car tells us which it is.

We charge a £20 call-out plus £20 for the diagnostic to read the car and tell you exactly what's triggering the light, and that £20 comes off the price of any work we then do for you. You get a clear picture before spending anything on parts. Send us your reg for a quote.

It can. A filter that's been removed or had its insides gutted is an automatic MOT failure, and the tester checks for that. A car smoking badly because the filter is blocked can fail on the emissions test, and if the fault has also brought the engine management light on, that's a fail on its own. It's worth getting the DPF sorted properly before your test rather than after a fail.

Related

All dashboard warning lights Diagnostics & fault finding Engine management light What is a DPF? Get a free quote What repairs cost

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