Check engine light only comes on when gas tank is 1/4 full

Update to my problem —-
shop could not find a problem for this code. Everything checked out just fine. Getting piised about the light coming on I tried the old "Witch Hazle/Snake Oil treatment I have used for years... Big dose of Marvel oil down the tank and in the oil —- WTH —- Have not had the light since. Do not understand why BUT ok-— -no light and clean smog check for registration in Nevada ——
what does WTH mean? Can you give more detail?