Hi Dennis,

I'm not sure there is an easy answer for this one. I guess (and this is a guess, and it is what I would do at the shop...while intoning a bunch of Volvo mantras - kidding - sort of...) since these buttons are very much akin to a switch, I would pull the radio (if you haven't done this before, push in those tiny rectangles you see on either side of the radio, and then pull out the little tabbies, and yank the radio...unhooking the antenna and other connectors from the back. Don't worry, they only go on one way.) spray computer keyboard cleaner (it's kinda like freon) all the way around the number four in the crevice, and then pretend your finger is a strobe light, just rat-a-tat very quickly and repeatedly on that four button...and hope.

I've made all kinds of switches work again that way...window switches, sunroof switches, mirror adjustment switches...etc...

I hope it works for you; nothing ventured; nothing gained...

Chris