Conditions for Setting the DTC
WARNING: This page is about a different car, the 2004 Suzuki Swift + and 2004 Chevrolet Aveo. However, it is still accessible from the selected car via links, so may be relevant.
DTC C0018 can only be set with the key in the ON position, the pump motor is commanded ON, and the EBCM detected a short to power or high resistance in the pump ground circuit.