Hi I recommend talking to your Nissan dealer and asking them to reset the computer back to original factory settings. I drive a Nissan Pathfinder which normally gets 28 on the freeway and 18 around town. But after several minor visits to the dealer for things like oil changes, and tire pressure warnings I was getting less than 14 miles per gallon all around. I pushed the service manager and he agreed to do the reset. They talked to the corporate office and performed the reset. Then they drove it around for several hours to reprogram the computer. They denied anything was wrong with it but when I got it back it was back to 28 miles per gallon on the freeway and 18 miles per gallon around town.
