This fault refers to a problem with the sensor communication system. Use the Sensor Checkout screen to determine which sensor is causing the problem. If all sensors are not communicating, diagnose as a communication bus problem. In other words, check the sensor communication cables. The easiest way to isolate problems with sensors or sensor cables is to disconnect all sensors and reconnect one at a time. After locating the sensor that is causing the problem, disconnect the sensor from the sensor cable and reconnect the sensor directly to the blue box. If the sensor works properly, then the cable is bad. If the sensor is still not working, then the sensor should be replaced.