P0440 code coming back monthly on 1997 Nissan Sentra GXE

My 1997 Nissan Sentra GXE 1.6 automatic transmission started to get both P0446 and P0440 codes a few months ago. I bought a new gas filler cap and the P0446 code went away. I am getting only P0440 code every month now. I know the new cap is holding vacuum because when I unscrew it, air hisses in to fill the vacuum. What could be causing this and how to fix it?

DTC P0440 indicates a large leak has been detected in the EVAP system

DTC P0446 indicates that there’s a problem with the vent valve circuit of the EVAP system.

If the vent valve doesn’t close when the EVAP system performs its self-test, you get a P0440 code.


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