Theomv:
Is that correct? Shouldnt it say Invalid CRC or something? If this is normal what can i do to print out to me that a sensor is disconnected?
Well, you calculate the number of attached sensors when you start up and display that number. Then you read all the attached sensors into an array that can hold 2 sensors (which will cause memory overwrite problems if you ever have more than 2 sensors attached). Then you average the first two sensors, even is one of them doesn't exist. Naturally you will get incorrect answers.
If you find that only one sensor is attached you should fail at that point rather than going on to average two sensors.