Q: What does it mean for a nissian maxima 2007 for a service engine soon

When the check engine light is on, it means that the ECU has detected a malfunction that will affect emissions. In your case, if the Auto Zone guys suggested that the gas cap was loose, then you may have had a P0440 code. Which might indicate an air leak in the fuel vapor recovery system. The gas cap is the simplest thing that can go wrong, but if that was not a successful fix, then you may have a leak in a vent line somewhere. The most convenient way to deal with this problem is to contact Your Mechanic. They can send a technician to your home or office to check out your Nissan and make a recommendation as to how to fix it.