[Tannaton]

On the XC90 there are more than one washer pump (depending on year) but the headlight washer pump is bigger and higher pressure than for the windscreen. It should only operate when the headlights are on and I think every 5th application of the jets.

My suggestions would be to remove the washer reservoir (easy to do, peel back the RHS of the bumper) and strip and clean it - there is a filter on each pump that can get blocked. Check also a hose hasn't come off and water leaking in the bonnet area somewhere.