That is standard for japanese radios. They will not go past 90 FM.
Ask a radio shop if they can do something on this, but probably you can scrap it.
You will find some more items on your car which are Japan specification only, such as the temperature sensor at the back of the cat.
But this sensor has no influence on the MOTRONIC, just gives a warning if the temp goes to high to avoid a fire when the car is parked on dry grass etc.
There is also a special replay for this, only Japan spec cars have that.