What voltage you are using to power the ds18b20 probe, 3.3V or 5V ? what resistor value? If you are using 3.3V and 4.7K, then I;ll recommend trying 5V and 10K resistor just to test things out.
Check hardware.
1) Power down the system and check for continuity across the ds18b20 wires, across all the female audio connector ends (or whatever connector you are using)
2) Power up the system and check voltage reading across the female connector ends. both data and +ve ends.
3) Check `dmesg` log for any kernel error related to ds18b20 (just type dmesg in your terminal)
4) Is the probe getting hot? sometime the wiring is reveresed and it can really heat up the probe (other than the fact that it does not get detected). Be careful, i have burned my finger by this

, and I know another person in r2r also experienced the same.