Garage door will not close; opener lights flash 1 time, pause, then 3 times repeatedly (logic board LED code 1-3).

Safety first: Disconnect power before handling wiring. Never operate the door with sensors removed or bypassed except for brief testing by a qualified person.

Steps to fix:

• Check sensor LEDs: If either sensor LED is OFF, there is likely a wiring or sensor failure. Confirm both sensors are firmly snapped into their brackets and not dangling.
• Verify connections at sensors: Inspect the wire nuts or push-in connectors at each sensor. Tug gently on each wire to ensure it is secure. Re-strip and reconnect any loose conductors.
• Check continuity: With power off, disconnect the sensor wires at the opener. Use a multimeter set to continuity to test each pair from opener end to sensor end. Replace any run that shows open circuit.
• Swap sensors (if identical): Temporarily swap the left and right sensors. If the problem follows the sensor, that sensor is defective and should be replaced as a pair.
• Reconnect to opener: Reattach the wires to the correct sensor terminals, ensuring no copper is exposed beyond the terminal.
• Power up and test: Restore power and attempt to close the door. If the 1-3 code persists with known-good wiring and sensors, the logic board sensor input may be faulty and require replacement.