Hw can i clean the rear sensor?

Hello, I don't know of any scan tool that can tell you there is debris on a sensor. And what sensor are we speaking of? If you know what sensor is related to a fault code, you should inspect the sensor for proper operation and condition physically. You would also want to monitor data from the sensor actively. I'm guessing you mean an anti-lock brake sensor, so check this and utilize test equipment that can monitor sensor data.