What sensor can cause F09 fault? Machine stops, clothes are still wet.

During the cycle my machine stops running displaying F09 fault. The cloths in the machine are still wet. I can restart the dryers, but sometimes it stops again, sometimes it keeps running till the end. When the machine complete the full cycle, sometime cloths are still not dry however the sensor should measure this. How can I find if the humidity sensor is failing or the over temp sensor is failing or......