00665 Seatbelt warning lamp K-19 (Limp Mode)

Bought an A3 2006 1.9tdi last year, just recently it has been loosing
power in the same place, up a slight incline. Put it on the diagnostics
and it is coming back with the following message "00665 Seatbelt
warning lamp K-19", repeatedly clear this code and the same loss in
power keeps happening at the same place, it's driving me mad. This
error surely can't be causing a loss in power, it's almost like going
into limp mode, no turbo and struggles to get any speed. I can pull
over turn off and on again and it works like a dream until the next
time.



Any support welcome, just want to rectify this problem asap as the car itself is great to drive.



Matt.