How to tell if your garage sensor is bad?

You can tell if your garage sensor is bad by looking for several persistent symptoms that do not go away after cleaning and realignment. First, check the LED lights. If one or both sensors have no light at all even after you have confirmed the opener has power and the wiring at the motor head is tight, the sensor may have an internal failure. Second, if the green receiving light continues to blink or flicker no matter how carefully you align it, and you have confirmed there is no obstruction, dirt, or sunlight interference, the sensor's internal photodiode may be worn out. Third, test the door behavior. If the door will not close from the remote or wall button and only closes when you hold the wall button down continuously, that is the opener's override mode indicating it thinks the sensors are blocked or bad. Fourth, swap tests can help. You can try disconnecting the sensors and touching the wires together briefly to see if the opener clicks, but a more definitive test is to install a known good sensor pair. Other signs include physical damage like cracked housing, water inside the lens, corroded wires at the sensor, or a sensor that gets extremely hot. If the sensor fails the cardboard box test where blocking the beam does not cause the door to reverse, it is definitely bad.