Most of the people on this forum don't have diesel engines, as they are not available in North America. (Though we wish it was!)
I would guess that you probably have an OBD code (check engine light). If so, you should have the code read, and that will shed some light on what you need to fix.
It sounds like your engine is being de-rated, which happens when there is a fault in the regeneration system (DPF). Reseting the battery might help, but I doubt it. You probably need to perform a forced regen, and I have no idea if you can do that yourself, or if it needs to happen at the dealer.