On my 2004 MDX, last week my malfunction indicator light (the engine icon on the dash) came on and stayed on. I took it to the dealer. They checked the codes, which indicated an evaporator leak in the system. They then checked all the lines, and found a cut in the fuel vent tube, which looked almost like it had been sliced open. What's weird is how this might have happened, since that whole area is covered and protected by a plastic shroud.
The tube they replaced is the "FUEL VENT TUBE A" (p/n 17713-S3V-A50), shown as #19 in the CANISTER parts diagram below.
It was an inexpensive fix, even with the 1.5 hours of labor to diagnose and find the problem. (I had to go back because they didn't have the part in stock.)