This has been an ongoing problem for many owners of many different makes and models of cars fitted with Diesel Particulate Filters (DPFs). The process of dumping fuel into the engine is designed to get the exhaust system hot enough for the DPF regeneration (self-cleaning) to take place. But a car that travels 500km per week really shouldn’t need this as the exhaust system should be getting hot enough in the normal course of things.

Either way, if you constantly have excess fuel being dumped into the engine, some of it will find its way into the sump (as you’ve discovered). That’s when the check engine light signals the problem, but in the meantime, you’re also driving around with engine oil diluted by the extra fuel. And that’s when engine wear can occur because diluted oil isn’t able to protect the engine’s metal parts as well as it should.

It could be that the car’s sensors are giving the computer the wrong information on how hot it’s getting, and/or how dirty the DPF is. Perhaps the DPF itself is damaged to the point where it won’t regenerate fully. A diesel specialist would be a good place to start, as this problem is hardly unknown these days.

This is a very common problem for owners of modern turbo-diesel cars who only do short, stop-start runs in city or suburban traffic. When the engine and exhaust can’t get hot enough for a DPF burn-off, the computer dumps extra fuel into the engine to get everything hot. If some of this excess fuel gets into the engine’s sump, it can force the level of the sump to rise, leading to the warning light you’ve just seen.

In the worst-case scenario, this fuel in the sump will dilute the lubricating oil and that can lead to a damaged engine. But as you’ve found, even if that isn’t the case, there’s still a price to pay to manually force the DPF to burn off as well as change the oil for fresh, undiluted stuff.

The solution is to make sure you drive the car for at least half an hour at freeway speeds once or twice a month. That will get things hot enough for a complete DPF burn and will keep you out of the workshop. Mind you, making this sort of effort might cost you more than the fuel savings you gain from owning a diesel car. This is just one reason a modern turbo-diesel is not ideal for every consumer.

This is a pretty common type of question these days. Once cars are out of warranty (and often before that time) many owners elect to use an independent workshop for their servicing rather than a dealership. But some non-dealership workshops don’t always know the little tips and tricks including how to switch off the service reminder after the scheduled service has been performed.

But here’s something you can try at home which should cancel the service light on your ASX. Turn the car’s ignition off. Now press the info button (down low on the dashboard near the steering column) until you see a small spanner icon appear in the info panel on the dashboard. Now hold down the info button until the little spanner symbol starts flashing. Once it’s flashing, release the info button again and the word `clear’ should pop up next to the spanner icon. With `clear’ displayed, press the info button one more time and you should be done. Now start the engine to make sure the service reminder light has gone out. If none of that works, a Mitsubishi dealership should be able to switch off the light for you.