It was late in the evening. My wife had just come home. The garage door did not want to close when she pressed the button on the remote. It had worked just fine a few hours earlier. My tools are in the garage. Leaving it open all night is not an option.

Step 1: Force It to Close?

This is the hard wired switch on the wall. She was able to make it close by holding the pressure plate on the switch down until it had closed.

Step 2: Signs to Observe

The light on the ceiling mounted opener flashed as she held the wall switch down to close the door. That is not normal.

Step 3: The Sensors

This is one of the sensors. There are two. One sends a beam of infra-red light to the other. If anything interrupts this beam of light, the garage door will not close and the ceiling light on the opener mechanism will flash as mentioned in the previous step. This is, of course, a safety feature to prevent the heavy garage door crushing anyone or anything that might be in the pathway of the door when it comes down. Check to be sure no child's toy or anything else blocks the path for the infra-red light beam.

The text box feature would not save when I did this Instructable, so I am overlaying colored arrows as keys to my explanation.

Most garage door problems can be traced to the sensors. The circuitry inside the sensors is quite reliable and has a long life. The first thing to check is the mounting brackets (blue arrow). Did something bend them so the sensors are no longer aligned? A quick visual inspection of each should be sufficient. In doubtful cases, you can stretch a long string between the sensors to see better if they are aligned.

The red arrow points to the LED. Each sensor has an LED. It should be bright and show a solid color. Some are green and some are red, depending on the manufacturer of your opener unit. One sensor on our unit showed a bright steady LED. The other, this one, was weak and it fluttered rapidly. That, together with the flashing ceiling light and the need to hold the switch button, are signs something is not right.

The yellow arrow points to the lens. It should be clean on both sensors. This garage is my workshop. It is always possible sawdust could have accumulated on the lenses. As a precaution, wipe them with a rag or a tissue.

The green arrow points to the wire that runs between the sensor and the opener unit on the ceiling. Look for obvious physical damage (bare wires, loose connection, cut or broken wire, etc.)

Step 4: What, Exactly, Could Be the Problem?

We do have a manual for our opener unit, but its troubleshooting section tells you how to check a few basic things, and then says, "You may need to call a technician for repair service." I am not much in the mood to wait for a technician at the time I want to be going to bed, if I can find one who will come late in the evening.

It has been two years since I had problems with a garage door opener, and that was a different unit than this one. I forget the procedure for troubleshooting one of these units. I have come to go on-line for help on the occasions when the garage door opener fails to work. After a quick search for "garage door opener troubleshooting," I opened this page. There are some general help pages, but they do not offer much more assistance than our manual and its suggestion to call a technician after checking a few basic things like obstructions to the infra-red beam and power to the circuit.

Help suggestions are often very brand specific. The image with this step is a chart for diagnosing problems with the sensors on a Genie garage door opener. Look closely and you can see that Genie gives diagnostic clues and codes in how many times the LEDs flash and in the color of the LED that shows something unusual. Our unit is not a Genie, but a Liftmaster. The help sections for Liftmaster units are more general and not very helpful.

Step 5: The Solution

I know from past experiences that the electrical connections to the sensor must be good, or the door opener does not work properly. I had already checked for obstructions to the infra-red beam, for power to the system, cleaned the lenses on the sensors, checked for alignment of the sensors by looking for bent brackets and so on. I grasped the small plastic plug at the end of the wire and pulled it out of its socket on the sensor. It required quite a strong pull. Do not pull on the wire, but on the plug. It may seem there is a catch that must be released first, but there is not. When I put the plug back into its socket, the LED no longer fluttered and the garage door worked properly once again. In time these connections corrode slightly with oxidation. Breaking and making the connection again is enough to restore its function. And, I did not need to call a technician.