Important: In order for the DURAMAX diesel fuel system to work properly, the fuel lines must be full of fuel and contain no air. If air gets into the fuel lines, it will be necessary to prime the fuel system to eliminate the air before operating the vehicle. Air could have entered the system in one of the following ways: • The vehicle ran out of fuel. • The filter was removed for service or replacement. • The fuel lines were removed or disconnected for servicing. • The fuel filter water drain cock was opened while the engine was running. If one or more of the above occurred, air has entered the fuel system and you will need to prime the system prior to operating the vehicle.