In my experience, it sounds like the nozzle might be clogged or bad. They can go after awhile or if theyíre hit with a lot of pressure, like if youíre scrapping snow off the car during winter or take a power washer to clean the car, so thatís a possibility. They're really just cheap plastic and easily damaged, unfortunately. When I first bought my G6 years ago, I got eight free oil changes from the dealership. When I brought it in during the winter, a dealership mechanic wiped snow off with his hand and took the nozzles right with it. If you need to replace them, the dealership charges a fortune (of course) and I donít think parts stores are allowed to sell them. You can find them easily at wreckers or online and you can get the part number from the dealership to get the right ones.
If I were you, Iíd start with what Maty suggested and see if something's wrong with the nozzle. If itís a clog, you might be able to shoot compressed air through the nozzle with an air compressor or even a computer keyboard spray to clean it. After that, Iíd check to see if you have problems with any loose connections or if the line is leaking. Chances are, and fingers crossed, the nozzleís either clogged or a connectionís been slightly dislodged. If it doesnít work after either of those, your best bet is to get a new pair. If you go through the dealership, it can be $30 per nozzle, but I've seen some online for $3 for two.
Hereís a link with an idea of shooting compressed air to clean it out a bit.
Pontiac G6: Ive got a 2006 Pontiac G6 and my Windshield Washer
Hereís a link for a video on cleaning out the nozzle. The carís different than a G6, but itís the same principle.