@uwefed
Danke für die Hilfe 
Jetzt funktoniert alles wie es soll ^^
@Doc_Arduino
Ich hab nichts in der Leitung hängen. Hab mich auf ein Tutorial verlassen:
http://blog.oscarliang.net/raspberry-pi-arduino-connected-i2c/
How Does It Work? Is It Safe?
The Raspberry Pi is running at 3.3 Volts while the Arduino is running at 5 Volts. There are tutorials suggest using a level converter for the I2C communication. This is NOT needed if the Raspberry Pi is running as “master” and the Arduino is running as “slave”.
The reason it works is because the Arduino does not have any pull-ups resistors installed, but the P1 header on the Raspberry Pi has 1k8 ohms resistors to the 3.3 volts power rail. Data is transmitted by pulling the lines to 0v, for a “high” logic signal. For “low” logic signal, it’s pulled up to the supply rail voltage level. Because there is no pull-up resistors in the Arduino and because 3.3 volts is within the “low” logic level range for the Arduino everything works as it should.
Remember though that if other I2C devices are added to the bus they must have their pull-up resistors removed.
Aber ich werde wahrscheinlich einen Bi-directional Logic Level Converter dazwischen hängen ^^