What To Do When Your DPF Light Comes On

What To Do When Your DPF Light Comes On

All of today’s motor vehicles have an array of warning lights that illuminate upon starting and then extinguish immediately, demonstrating that all systems are go. If the car in question is a diesel vehicle then an additional light for the correct functioning of the diesel particulate filter (DPF) is included. As with all warning lights, if it lights up and stays lit, then the driver has an issue that needs looking at, pronto.

About The DPF

As the name suggests, the DPF collects the impurities arising from diesel fuel emissions as required by state rules and regulations. The DPF quietly gets on with the job underneath the car without any interference from the driver. However, from time to time, mileage depending, it does require occasional maintenance to run at its best. It’s a very important automotive part. Your local car servicing garage can advise on correct procedure regarding the cleaning of the unit, but there are steps an owner can take:

Diesel particulate filters, if properly maintained, can have a long life. However, over a considerable period of time, a diesel particulate filter can become clogged up by the soot from engine exhaust.

A good point to note is that, clogging will happen sooner if a vehicle is used only locally with little running at highway speeds, as on a motorway for example. When the DPF becomes clogged the performance of both the filter and the car suffers. This will be noticed as a marked drop in performance or even a shift to ‘limp’ mode depending upon the model. Whatever, the DPF has to be cleared.

The aforementioned dashboard warning light will identify the issue. The ‘how-to self-clear the DPF’ is all in the manual for the car but, failing that, for best results the job should be handled by a professional garage, perhaps as part of a routine interim service. A properly functioning DPF is a requirement of the MOT test. So, if the car’s DPF light comes on and stays on, here are some tips to help remedy the situation.


There are certain actions an owner can undertake that will help the system to ‘regenerate’ and clear itself. For example, a half-hour high-speed run (up to 70 only, obviously) on a major road or motorway will have the effect of ‘burning off’ any residue in the filter. This is called ‘passive’ regeneration. Clearly, if there’s a passive method it makes sense that there must be an ‘active’ method too.

Active regeneration of the DPF normally does not require any external tools or products. It is in fact a state of running built into your car’s engine control unit (ECU) by the car maker. Once in this state, the engines air-fuel ratio will be altered to raise exhaust temperatures and as a result of the very high temperature will allow the DPF to clear. Some cars may need an external software tool to be plugged in, in order to activate this state, in which case consult the garage.

When That Doesn’t Seem To Work

Since the introduction of the DPF, professional garage services began to offer a cleaning service. Your local garage, (Note: only if suitably equipped with the correct specialist equipment), can, by process of ‘forced regeneration’ get it running properly once again. This is best left to the experts: The correct diagnostic or reset tool must be used and the job could take up to thirty minutes or so. The car servicing garage will ensure that the regeneration process is conducted in a safe environment as exhaust temperatures will be very high.

Don’t even think about removing the DPF. It’s illegal and will invalidate insurance. Far better to keep it running correctly. If the car is getting older, why not make it a part of the annual car service? Of course it costs money; anything to do with cars does, but the improved fuel consumption and smooth running of the vehicle will be the payback. As sensible owners know, a well maintained car will always have better economy and reliability. That’s got to make for worry-free motoring.

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