I had my check engine light come on last week. I took it in to the closest dealer and they called and said it was the valve in the supercharger. Apparently this valve opens and closes allowing the air to build up hence the boost. The nissan dealership told me this would only happen if I was not putting premium fuel in my tank. Since I bought the truck off the lot I've been putting premium grade fuel...91 or better. They didn't believe me. When I asked what else could cause that I got no answers. The car orginated from the east coast (philly)...I've been in Arizona for almost a year. Is there something that AZ puts in the gas for emissions sake that would be different on my truck then PA gas. How about elevation change? Does this have some effect on the supercharger valve not opening and closing? My truck has always had premium fuel...I just find it hard to believe that caused the problem when I was doing what the manufacture suggested all along. Does anyone have an answer for me to put closer to this issue?