Hello, If you have a pop rivet gun-you'll need 5 or 6 rivets-and a drill, I suggest this from my recent experience with a 0442 code. My fuel filler is on the RR quarter panel (2002 V70 base). Remove the RR wheel and plastic wheel well liner. Mine had 3 10mm nuts and 5 pop rivets which need to be drilled out. Just remember you're working with soft plastic and you don't want sharp tools wandering off their mark. You'll see the inverted air filter for the EVAP system hanging next to the filler neck. I put a short section of old garden hose on the thing and blew into it gently. I located my leak from the hiss. In my case there was a small leak in my J hose. My J hose, a valve and the charcoal canister were all together in the center of the vehicle between the rear wheels immediately ahead of the spare tire well. Tipping the rear of the exhaust system down-all small hardware-is all I needed to do. Believe me it's no big deal to look. The hardest part of the job was removing the factory crimped hose clamps.
You could ask at a dealership if your car has a J hose. There are differences among models and your mechanic might be mistaken.
J hose,$26. 2 Ideal clamps,$1.80. Advice from the wonderful people on this board and the feeling from fixing a problem yourself, PRICELESS. Kira