Hi, you can try this to get rid of your warning light... I have a 2005 2.8jtd, Ci 171 and had the same light with occasional loss of power.
After a deep search of the internet I found that the turbo wastegate actuator eye end can start to seize on the pin of the wastegate valve lever, making the w/g unable to travel to it's full extent.
If you crawl under the van, head first from behind the offside front wheel and look forward and up, you will see the vacuum controlled actuator, just at the start of the exhaust. There is a circlip holding the eye end onto the pin, remove it and try and lift off the actuator. (You may have to remove the bolts at the actuator body bracket to give you more 'leverage') Clean the pin and actuator eye end inner with scotchbrite or similar, use a small amount of light oil to reassemble and go for a drive!
I had to do this to mine in France in 40° heat recently as I was about to do the 'Route des Grande Alpes' and the van drove superbly after
Hope this helps