Engine management light?

I have a fiat punto 1.3 Multijet and am very happy with it. That was until the engine management light came on and the turbo cut out (at about 3000 reves) on a duel carriageway. The bizarre thing is that if I stop and turn the engine off the turbo will come back until the EML comes on and goes off again.

I've taken it to garages and they have said that they can't find any error codes. That was until a message came up on the diagnostic machine saying "B1D6 unknown error". Can you shed any light?

Cheers Matt