Posted: Jul 16 2009 at 10:32am | IP Logged

I found this on another website, called my local Nissan service manager and he verified that it is correct. If the battery goes dead or you disconnect it for any reason it can screw up your mileage:

"I found out why i was getting 10 mpg..........mechanic plugged in computer and found my engine at 86% , he re-set everything and told me to go from his shop to highway but to keep rmp's from 1,000 to 1,500 while the computer went through its re-learning process according to the driving habits... then on highway to get to 60 mph and keep it there for 15 to 20 minutes............ on sunday i went on a 253 mile trip and my mpg was at 20.++ drove through mountain areas at 70 to 80 mph... everything back to normal.. so if you have disconected your battery for any reason .. chances are like myself i simply began to drive as usual and it caused my air/fuel mixture to be set abmormal causing my horrible mpg..... some nissan owners have said that after service their mpg went down.............it might be from the battery being disconected............ "