2006 citroen xsara picasso 1.6 diesel, losing power ?

As above there are many reasons for theEML lamp being lit. The first thing is to get it scanned, the fault codes will give a path to investigate. You haven't stated the mileage but if it is around 70k it could mean a new fuel filter or a refill of the Eolys Fluid (fuel tank additive).

Badger33
April 2014

When was it last serviced properly?

Have you checked your air filter recently. Could be dirty and blocked if not renewed lately. A replacement will cost about a fiver.

If it is not that then could be fuel filter or DPF.

Getting the fault codes read should point you in the right direction.

ChicksFan
February 2014

1st you get it scanned for fault code then you get told it could be x,y or z getting more and more expensive as they go and hopefully one of the bits they fit fixes the car before you have to declare yourself bankrupt.

EX 1.6 Xsara picasso diesel owner
February 2014