Pathfinder 2000 SE 110K. The "Service Engin Soon" light comes on and goes off. I got it free checkup from local auto part store and the following "Nissan troble code P1491 Manufacturer Specfic Powertrain Trouble" showed up. I was told not to worry about it and the code was cleared free of charge. After week or so the light came back on, same results P1491. I however did some research and the following "CodeVacuum Cut Valve Bypass Valve" explanation given for P1491. Can any one please help me to understand this? Can I fix it my self? Thanks.