i am actually facing the same issue as well.
my LED keeps flashing level 1 but my tank is full. after awhile it will go off, i realise that once i park on a slope or stop on itm the error code will come back. my tank is full with water/methanol 50/50.
i read that some sensor might have problem with colorless liquid? is it advisable to put very little of coloring into the mixture so it will help the sensor to detect better?
here is the video to my flashing problem when my tank is full.