1. Check if each sensor is mounted.
  2. If an error occurs when checking the CS31A (3 CST FM B/D CN3) disconnection operation, replace a sensor.
  3. If an error occurs when checking the CS31B(3 CST FM B/D CN3) disconnection operation, replace a sensor.
  4. Check if the CDU Board CN6 and 3 Cassette FM Board CN1 are connected.
  5. Check settings of 3 Cassette FM Board Dip Switch (#2, #4, #6 On)