ignition, fuel system

P1258 is low coolant level, P0303 is a misfire code for cylinder number 3. I would see if the coolant level is low and top up the coolant level as required. Does the engine run rough? Perhaps you have a bad spark lug or coil failure. After topping up the coolant level , turn of the light and drive, check the coolant level again if it down perhaps you have a coolant leak. The way an automotive shop would locate the leak is by removing the radiator cap and attaching an adapter that screws on in place of the radiator cap. Something that looks like a bicycle pump with a pressure gauge attached to it is used to "pump up" pressure to simulate pressure generated when the cooling system is at operating temperature, the leak is then found sometimes it is obviously leaking from a coolant hose or cracked housing, failed gasket or water pump, sometimes the engines cooling system needs to be inspected from below or inspected using a mirror and flash light. If the engine runs poorly and the ignition system is found to be OK you should have the compression checked and or a cylinder leakage check performed as it is possible you have a blown head gasket on number three cylinder or less serious a leaking intake manifold gasket or other issue but get this looked after before more serious damage occurs.