DPF warning light: what to do next

If a DPF warning light comes on, the filter in your diesel exhaust is starting to clog with soot and needs a chance to burn it off. Do not ignore it and do not keep making short trips. Check your handbook, because the wording and the correct response differ between makes and models.

Many cars will clear the problem themselves if you drive at a steady speed on a road where that is safe and legal, for a sustained period. If the light stays on, flashes, or arrives with an engine management light or a loss of power, the car needs checking by a garage before the filter is damaged.

What does the DPF warning light actually mean?

The diesel particulate filter traps soot from the exhaust. Over time it fills up, and the engine management system clears it by raising the exhaust temperature so the soot burns away. The warning light tells you that process is not completing, or that the filter is nearing its limit.

On many cars it is an amber symbol showing a box with dots. Some makes show a message instead. The light is a prompt to act, not a sign that the engine is about to stop, but it should not be left for weeks.

Why does my DPF keep blocking up?

The most common reason is the way the car is used. Regular short journeys, slow town driving and frequent cold starts never get the exhaust hot enough for the filter to clean itself. Soot then builds up trip after trip.

A fault elsewhere can also be behind it, and a clean filter will simply block again if the cause is not found.

• Mostly short, low-speed journeys
• A faulty sensor reading the filter pressure incorrectly
• An injector, EGR valve or turbocharger fault producing extra soot
• Oil that has not been changed to the correct specification
• Interrupted regeneration cycles when the engine is switched off mid-process

What can I safely try at home?

First read the handbook for the manufacturer's advice. Where it says a longer run at steady speed helps, choose a clear road where you can hold a consistent speed within the limit, and keep going until the light goes out. Never speed to burn off a filter.

Check the basics too: fuel level, oil level and any other warning lights. If the car feels flat, smells of fuel, or the oil level seems to be rising, stop relying on driving it clean and have it looked at.

What will a garage do about a DPF warning?

We start with a diagnostic scan to read fault codes and the pressure and temperature data around the filter. That tells us whether the filter is simply loaded with soot, or whether a sensor, injector or valve is the real cause.

Depending on the result and the vehicle, the work might be a managed cleaning process, repair of the underlying fault, or in some cases filter replacement. What the job involves and what drives the cost depends on the vehicle, the condition of the filter and whether other parts are affected, so we cannot promise a repair before inspection.

When should I stop driving with a DPF light on?

Stop and seek advice if the light flashes, if the engine goes into reduced power, if there is white or black smoke, a strong smell of fuel, or any warning that tells you to stop. Carrying on can damage the filter, the turbocharger or the engine.

If you are unsure, it is safer to have the car checked than to keep driving and hoping. A quick call to ask about a booking costs nothing.