i'm getting "internal control keep alive memory?" for fault p0603. which i think has nothing to do with using coolant. i assume you're finding no leaks, so it's leaking somewhere you can't see. does it smell of antifreeze in the interior? is the carpet wet? the heater core might be leaking into the interior. there could be a slow leak on the top of the engine and it's boiling away before it has a chance to pool. fill your reservoir . let the engine get hot. inspect for steam in the engine compartment.
the code you have P0603 check 12volt battery cables make sure they are clean with no corrosion, clean cables and terminals. the code may need to cleared or it may reset itself. As for using coolant ckeck the oil,and also check the transmission fliud if it is light rusty color or way past full you need to replace the radiator then have transmission flushed.