It is most likely the sensor, but something is caused the problem. The #1 thing I have found that causes the rbas to set a code is a broken wire leading to the sensor. Check the wireing harness for the sensor for any damage, if there isn't ant you might want to pull the sensor and look for any signs of damage to it. If there is damage to the end of the sensor it most likely was hit by something inside the diff. If this is the case, you'll want to remove the diff cover and inspect the insides for ant signs of damage (ie. broken tone ring, chips missing from ring, pinnion or spider gears, etc..)