I realized my accelerometer is not working because the auto-rotation stopped working. I checked with various sensor apps the accelerometer is not detected. My phone fell into a river, but after disassembly and drying everything except the accelerometer worked again.
Is there a possibility to replace the sensor or some “fancy” hardware reset which might jumpstart the sensor again ;). I have seen the forum thread about not functioning auto-rotating but I couldn´t find the answer I was looking for. Thanks for your help.