Garage door will not close; opener lights flash 1 time, pause, then 2 times repeatedly (logic board LED code 1-2).

Safety first: Unplug the Chamberlain opener before working on any wiring. Use a step ladder safely and avoid pinching wires in the track or hinges.

Steps to fix:

• Verify terminal connections: At the opener head, locate the sensor terminals (usually labeled SENSORS or with icons). Confirm the white wires are on the white/common terminal and the white-striped wires are on the sensor terminal. Correct any reversal.
• Inspect for shorts: Follow the sensor wires along the wall and ceiling. Look for spots where the insulation is crushed, cut, or stapled too tightly. Any bare copper touching another conductor or metal can cause a short.
• Isolate the fault: Disconnect both sensor wires from the opener. Cut two short test leads (18–22 AWG) and temporarily connect each sensor directly to the opener with these short leads. If the code clears, the sensors are good and the in-wall wiring is faulty.
• Repair or replace cable: If the in-wall cable is damaged, cut out the bad section and splice with wire nuts and electrical tape, or run a new 2-conductor low-voltage cable from the opener to each sensor.
• Retighten terminals: Strip 1/4 inch of insulation, twist the strands, and firmly secure each conductor under the terminal screws. Avoid stray strands that can bridge terminals.
• Restore power and test: Plug the opener back in and test closing. The 1-2 code should be cleared if the short or reversal is corrected.