Most garage door sensor faults are one of six things, and four of them you can check in ten minutes without tools. The order matters: a sensor that looks dead is usually just misaligned, and a sensor that is perfectly aligned can still fail the only test that counts, which is whether the door goes back up.
What the two sensors actually do
One unit sends an invisible infrared beam across the opening and the other receives it. While the beam is intact the opener is allowed to close the door; the moment it is broken, the door must stop and reverse. Since 1993, residential openers sold in the United States have been required to include this kind of entrapment protection, which is why a door without working sensors should not be operated at all.
The sensors sit four to six inches above the floor, one on each side of the opening, with the lenses facing each other.
The six causes, in the order to check them
- Something in the beam. A bin, a hose reel, a bike wheel, a car mirror. It sounds obvious and it is the most common call we get that needs no repair.
- Dirty lenses. Salt film, dust and spider webs are enough to break the beam. A dry cloth on both lenses fixes more sensors than any part we sell.
- Misalignment. The bracket has been knocked or has drifted. The receiving light will be dark or flickering; move the eye slowly until it goes steady.
- Low sun. If it only happens in the late afternoon, the sun is saturating the receiver. A small shade or turning the bracket a few degrees solves it, and this is a South Florida problem more than a hardware fault.
- Damaged wiring. Corroded terminals at the motor head, or a cable nicked by a ladder or a lawn tool. The light may come on and the door still not reverse.
- A dead sensor. Water inside the housing, a cracked lens, or a unit that stays dark after cleaning, alignment and a wiring check. At that point it is a replacement, and it is a replacement of the pair.
How to test it properly
Two tests, not one.
The beam test: open the door, put a box about a foot tall in the middle of the opening, press close. The door must stop and reverse without touching the box.
The force test: lay a piece of wood or a thick book flat on the floor under the middle of the door and close it. The door should meet the object and return. A door that only reverses on a solid block, or that pushes down before reacting, is not set correctly.
A sensor with a steady light that fails either test is not fixed. That distinction is the one most homeowners miss.
Repair or replace
Repair, in almost every case: realignment, cleaning, a wiring repair or a new bracket. Replace the pair when the housing has taken water, the lens is cracked, or the unit stays dark after everything else has been checked.
Replace them as a pair, always. Sensors are matched at the factory, and mixing a new unit with an old one is the most common reason a replacement still misbehaves.
What decides the cost
We do not publish prices, because the job varies: a realignment on a door with sound wiring is not the same visit as replacing a pair on a coastal door with corroded terminals. What we will tell you is what it needs before any work starts, and the estimate is free.
When it is not the sensor at all
If a known-good pair is fitted, aligned and tested and the door still misbehaves, the fault is in the opener’s travel limits or force settings, or in the control board. Raising the force setting to make the symptom go away is the wrong fix: it removes the protection that stops a door on a child’s arm.
What we do
We diagnose and repair sensors same-day in Miami-Dade and Broward, with a 100% workmanship guarantee and a free estimate. Palm Beach and the Florida Keys are scheduled by route. Call (305) 885-8088 or request a repair.
If you already know the pair is finished, our guide to sensor replacement in Miami covers the parts and the fitting step by step. If the door reverses with nothing in the way, start with why a door reverses before closing.