Nissan Maxima Owners Manual: Loose fuel cap warning
The LOOSE FUEL CAP warning appears in the vehicle information display when the fuel-filler cap is not tightened correctly after the vehicle has been refueled. It may take a few driving trips for the message to be displayed. To turn off the warning, perform the following: 1. Remove and install the fuel-filler cap as soon as possible. For additional information, refer to "Fuel-filler cap" in this section.
2. Tighten the fuel-filler cap until it clicks.