Is the plastic connecting link rod still attached? Have a look at the video below.
https://www.youtube.com/watch?v=TsltZXXnX3k
If the link rod has fallen off, its a £6 part from Volvo. You can do a DIY fix, as shown in the video above. Many say its not ideal, but loads of people have done it. The ball that the link rod attaches to gets worn with the movement of the link rod & the heat of the engine - General wear & tear I suppose. Then, the link rod has nothing to hold it in place & it falls off.
The link rod moves when you start & stop the engine, if its attached to the socket & ball of course that you can see in the video. The movement of the link rod in turn moves the flaps into the open/closed position as required.
Its a very common issue. I rang the local dealership to get a new link rod for my car & the member of staff I spoke to said that they stock them all the time, simply because they sell lots of them!