Thanks for your advice.
I have replaced
range = (highByte << 8 ) + lowByte; // Put them together
//print it
Serial.print(" Entfernung2: ");
Serial.println(rangeData, DEC);
delay(500);
with
range = (highByte << 8 ) + lowByte; // Put them together
//print it
Serial.print(" Entfernung2: ");
Serial.println(range, DEC);
delay(500);
and it works now.
Can i delete some parts of the code or can i make the code a bit shorter? Do you have any idea, or is it right now?