I have also attempted to perform this.
My findings:
If you remove/delete the Japanese maps, the ETC warning will disappear.
However, you may also lose the speed limit recognition.
I have also tried updating the maps & it seems to only recognize a USB with Japan map data.
My findings:
If you remove/delete the Japanese maps, the ETC warning will disappear.
However, you may also lose the speed limit recognition.
I have also tried updating the maps & it seems to only recognize a USB with Japan map data.