Symptoms of a bad garage door sensor, which are the small safety eyes mounted 4 to 6 inches off floor on each side of door opening that prevent door from closing on people or objects, include failure to close, reversing, and blinking lights. The most obvious symptom is door starts to close then immediately reverses and goes back up, with opener lights flashing 10 times, indicating sensor beam broken or misaligned. Opener wall button may only close door if you hold it down continuously, but remote will not close door, which is classic sensor issue. Sensor LEDs provide clues: one sensor should be steady yellow as sender, other steady green as receiver when aligned; if green is off, blinking, or flickering, sensor is bad or misaligned. Physical damage such as cracked lens, loose wiring, or water damage from overflowing gutters causing corrosion makes sensor bad. Sunlight shining directly into sensor can cause intermittent failure, especially at certain times of day. Wiring that is cut or chewed by animals causes intermittent open circuit. Dirt, spider webs, or cobwebs covering lens block beam and mimic bad sensor. If sensors are more than 15 years old, they may have failed circuit board. To test, try aligning sensors so they face each other exactly and clean lenses; if LEDs stay off despite power, sensor likely bad and needs replacement costing 20 to 50 dollars per pair plus 75 to 150 dollars labor if professional.
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