2001 Hyundai Elantra Question: I keep getting a PO440 code on my obd2

you may have several issues,poss vac leak,sensor or purge issue. seek a diag and est and don't guess it could get pricey

you need an evap diagnosis...somehow fumes are not being held in your gas tank

Are you using a 'code reader' or a real scanner? Readiness codes need to go through specific conditions or drive cycles to 'complete' will stay 'yellow as long as any item that applies is not 'complete'. Suggestion - get it diagnosed as globalhelper suggested , keep your fumes in your own tank. Once it's fixed and the code is cleared , it may take several days and a few hundred miles of driving to get all readiness codes 'complete' depending on driving style and conditions , but each time the codes are cleared (or reset) you must go through the driving all over again. Patience.good luck.