Service engine soon light was on for approximately 4 weeks. My local mechanic could not read the code on his computer. He suggested a software upgrade or update from Nissan might be needed. I went to Nissan garage to question them. They said there were some codes a generic machine cannot read. 2 Days Later, when I was getting ready to take truck to service center ,a the light went off, and stayed off. What was going on? Please.