The 'diesel filter' on your cars alarm message is a particle filter in your cars exhaust system that traps most of the diesel particles. The fluid is Eolys fluid that is automatically injected into the fuel each time you fill up.

The fluid helps the particles to burn more readily at a lower temperature.

The particle filter is meant to be changed or cleaned out at 50,000, or on later model cars 80,000 miles. The Eolys fluid is filled up at the same time so that the system works for another 50 or 80k miles.

Most garages will just change the filter which is where the £749 cost is coming from.

If you are handy you can remove the particle filter & clean it yourself with jetted water & fill the Eolys container, costs about £120 for 5l of Eolys.

Your car may just need a good run ie 20 miles up the motorway at 3000 revs & 70 mph which may clean out the filter. But if your car is one that needed the filter service at 50k it will only be a temporary fix.

Do a forum search on 'FAP' & 'Eolys' & you will get a good understanding of how the system functions.

Hope this helps.

This is not covered by a normal service.

It's really like a cam belt change.

Although it's needed at at certain mileage, it would be something agreed between the garage & custommer, probably at the garages recomendation.

Also it wil depend how the car has been driven.

If its had a lot of motorway use the filter will last longer than a car that has had a lot of town use.

But as i said above, your car may just need a fast run at highish revs to clear out the filter.

The cost quoted by your garage seems a bit steep, I think you could get thta down quite a bit if you shop around.