1999 Jeep Cherokee Computer Code PO455

My 1999 Jeep Cherokee Sport's check engine light recently was tripped. After running the code check, PO455 was displayed-EVAP large leak detected. The first and obvious repair was to purchase and install a new gas cap. After installing the cap and several miles later. The check engine light shut itself off. Is this possible? Does the computer sense the correction in the EVAP system and clears itself? Or does the light normally click off after time (even if a correction was not made?) Should I plug in the diagnostic tool again to see if the code still appears, even though the check engine light is no longer illuminated? Appreciate your help.