Ray 
2005 Nissan Frontier Crew Cab 4dr Crew Cab SE Rwd SB (4.0L 6cyl 6M)
Fuel Emissions Control Valve
 my wife drives this truck to her work on a farm, and the roads are somtimes muddy.  there was a build up of dirt and mud on the emissions control box on the drivers side rear wheel on the inside of the frame which caused the service engine light to come on, this build up of dirt cause the engine emissions control valve to fail.  Bad disign on Nissans part, there should be some sort of fender gaurd to prevent the build up of mud on the emissions box.  Great truck just don't drive in the mud to much.