Hi can anyone help me. I have an engine light on. My father in law plugged it in and it said it was the dpf filter. I saw on a forum that apparently if you drive for 20 miles in 3rd gear it may sort it. Anyway I am now 20 miles away and it didn't work. Has anyone got any ways that may work? I spoke to a car mechanic and he said it's very expensive to change.

I would try 4th gear for 20-30minutes keeping the revs steady. You need to get heat into the dpf to get rid of the soot build up.

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I doubt if the light will go out on its own, even if the dpf is cleaner now. It may need resetting.

A standard OBD reader may be able to do this, but a full diagnostic system  may reveal more. You will find a lot about ELM327 & Forscan on this site, which together provide a very comprehensive diagnosis & maintenance tool.

For ELM327 see:

http://www.spanglefish.com/TunnelratElectronics/index.asp?pageid=516992

One of these will pay for itself in no time.

you ill also need a program called Forscan, its free and you can get it from

http://forscan.org/download.html

I think Forscan can initiate a dpf cleaning cycle, and also identify if dpf fluid (if your car has it) is low. I don't have dpf, so I am not 100% sure, but there is loads of info around this site.

Yes Forscan can do a regen, the light will not go out on its own it needs resetting, if you don't have a code reader that can do resets the disconnect the battery for 20 mins this will reset the ecu, make sure you have the radio code and that you know how to reset the Windows.

when you first start the engine after disconnecting the battery the car will run rough for a few miles whilst the ecu relearns