Go to AutoZone & have them read the error code. Get the number, not just the guy's description, then come back. Even with the number, you still have to do some troubleshooting. For example I got P1457 EVAP canister system a while ago. There's a handful of solenoid valves, wiring, a 3-way valve, a pressure sensor, and a whole mess of vacuum tubing where it could POSSIBLY be leaking. You still have to find the leak.

Dark... If you REALLY know it's the valve, OK. That's what mine was, it was less than $50 & not too hard to replace. But still, you need to be sure it's actually the valve. It could just as easily be $1 worth of rubber hose that's torn, or a loose wire somewhere.