Drawbridge Failure Due to Safety Sensor or Limit Switch Fault

This is the most common cause. Access the simulator’s Motion Diagnostic Screen and locate the 'Bridge Stowed' or 'Bridge Raised' status bit. Use a multimeter to test the physical limit switch at the bridge's stowed position; the switch should toggle state when manually depressed. If the switch does not change state or the diagnostic GUI fails to reflect the physical position of the bridge, the sensor is misaligned, dirty, or faulty.

Sources