OBD II Serviceability Issues: Refueling
WARNING: This page is about a different car, the 2006 Suzuki Verona. However, it is still accessible from the selected car via links, so may be relevant.
A new OBD II checks the integrity of the entire evaporative emission system. If the vehicle is restarted after refueling and the fuel cap is not secured correctly, the OBD II system will sense this as a system fault and turn ON the MIL and set DTC P0440.