No power at 25 mph

Please can someone give me some advice.i have a 2006 freelander td4 auto. I love it and have had no real problems with it for the 3 years I've had it.
Yesterday I noticed, out of the blue, I could not get any faster than 25 mph and the engine warning light with the exclamation mark in it came on. I limped home very slowly.
Is there anything I could check before taking it to the garage I am trying to keep costs down and fore warned is fore armed,
Thank you for any help

Had same problem with my freelander 1 it turned out to Be MAP pressure sensor.do not buy an after market one it still did not fix it. Get one from a scrap yard landrover original . All this was done at a garage under it 3 mounts warranty hope this heps.