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How can you tell if a garage door sensor is bad?

Garage door sensors play a crucial role in ensuring your garage door operates properly and safely. These sensors detect when the door is fully open or closed and send signals to the garage door opener to stop and reverse the door if there is an obstruction. However, like any electronic component, garage door sensors can malfunction over time. Knowing the signs of a faulty sensor and testing methods can help you identify and resolve issues to keep your garage door working smoothly.

What are garage door sensors?

Garage door sensors, also known as safety sensors or photo eyes, are designed as a safety feature for automatic garage door openers. They consist of two small components – a transmitter and a receiver – that are installed on either side of the garage door opening. The transmitter has an infrared LED light that continuously sends out an invisible light beam to the receiver across the doorway. As long as nothing is blocking the light beam, the receiver sends a signal to the garage door opener that it is safe to close the door. If the light beam becomes obstructed, the receiver will not get the signal and tells the opener to stop and reverse the door.

Types of garage door sensors

There are two main types of sensors used for garage doors:

  • Infrared sensors – These emit an infrared light beam between the two units to detect obstructions. They have an effective range of around 30 feet and are the most common type used in garage door systems today.
  • Safety edge sensors – These sensors are mounted along the bottom edge of the garage door. If the bottom of the door hits an object as it’s closing, it will press against the safety edge and send a signal to stop and reverse the door.

Infrared sensors tend to be more sensitive and better at detecting obstacles in the path of a closing garage door, so they are the predominant type found in most garage door systems. The infrared sender and receiver are inexpensive components, usually costing $10-$30 each.

Signs your garage door sensors may be faulty

Here are some common signs that could indicate an issue with your garage door sensors:

  • The garage door refuses to close. This is the most obvious sign of a sensor malfunction. If the door gets partially closed and then immediately reopens, the sensors are likely obstructed or misaligned.
  • The garage door opener struggles to close the door. You may hear the opener straining, vibrating, or making noises trying to force the door closed. The sensors are not aligned properly.
  • The garage door closes unexpectedly. Faulty sensors may fail to detect obstructions. If the door closes without reversing, the sensors are likely dirty or non-functional.
  • The sensor light is off. The LED sending light on one sensor is burned out, indicating a problem with that unit.
  • Physical damage. Cracks, loose mounting, frayed wires, or corrosion indicate wear and potential sensor failure.

If you notice any of these warning signs, it’s a good idea to test the garage door sensors and verify whether replacement is needed.

Testing garage door sensors

You can test your garage door sensors yourself to determine if they are working properly. Here are two simple methods to diagnose issues:

1. Visual test

  • Look at the sensor units while the garage door is closed. The LED light on the sending sensor should be illuminated. The receiving sensor’s LED will light up when it gets the unobstructed signal from the sender.
  • Open the garage door. Both sensor LEDs should turn off when the door is fully open.
  • Partially close the door. The LEDs will turn on again when the sensors realign. Observe them to see if both lights come on steadily.

If either LED fails to illuminate or seems to flicker/struggle, there may be an issue with the sensor on that side. Visually inspect for damage, dirt, or misalignment.

2. Obstruction test

  • With the garage door fully open, place an object such as a broom handle directly in the path between the two sensors.
  • Attempt to close the garage door using the wall switch or remote. It should not close.
  • Remove the obstruction. The door should now be able to close properly.

If the door closes on the object between the sensors, it indicates faulty sensors that cannot detect obstructions. The units may need cleaning or realignment, but replacement may be required.

How to clean and realign garage door sensors

If the visual and obstruction tests reveal issues, here are some steps to try cleaning and aligning the sensors before replacing them:

  1. Use a soft cloth or cotton swab dampened with rubbing alcohol to gently clean the lens and housing of the sensor units. Dirt and dust can interfere with their functionality.
  2. Check for any spider webs, insect nests, or other debris obstructing the path between the two sensors. Clear away anything blocking the light beam.
  3. Carefully inspect the sensors and mounting brackets for damage. Fix any cracks or loose parts with adhesive or tightening hardware.
  4. Make sure both sensors are pointed directly at each other in alignment. Re-adjust the mounting angle if they have shifted out of position.
  5. Verify that the sensors are mounted at the same height and are level with each other.

After cleaning and realignment, conduct the visual and obstruction tests again. If the sensors pass both tests properly, the issue was likely due to dirt or misalignment. The sensors may work reliably again after the maintenance. However, if they still fail the testing, replacement of the problem sensor(s) is needed.

How to replace faulty garage door sensors

Follow this step-by-step process to remove sensors that cannot be fixed and install new replacement units:

  1. Unplug the garage door opener to cut power before replacing sensors.
  2. Remove the existing sensor units from their brackets by unscrewing any mounting hardware.
  3. Unclip the wires connected to each sensor. It helps to take a photo of the original wiring order to ensure correct re-attachment.
  4. Clean the mounting areas thoroughly to remove any dirt, debris, or old adhesive.
  5. Install the new sensors in the same location as original units, securing with appropriate hardware.
  6. Reconnect the wires to corresponding colors following manufacturer instructions.
  7. Perform alignment and testing of the new sensors to verify proper functionality.
  8. Re-power and test the garage door opener to ensure smooth operation without any sensor issues.

Carefully follow the included instructions for your new replacement sensors. While installing garage door sensors is not complicated, always ensure they are securely mounted and connected for safety purposes.

When to call a professional

Garage door sensors are simple devices that can often be tested and replaced easily DIY. However, there are some cases where a professional may be advisable:

  • If the sensors require any re-wiring of the opener/control unit.
  • For specific proprietary sensors that sync to the garage door motor.
  • If sensors are very difficult to access or require extension brackets.
  • Any time you feel unsure about safely mounting the sensors.
  • For general garage door opener maintenance, adjustments and safety checks.

Professionals can also evaluate your entire garage door system if you are having operating issues beyond just the sensors. Get a technician’s advice any time you are uncertain about DIY sensor testing and replacement.


Faulty garage door sensors can cause a major inconvenience and safety hazard if your door is not operating properly. But in most cases, you can identify bad sensors through simple visual and obstruction testing. Cleaning dirty units or realigning misaligned sensors may get them functioning again. For damaged sensors that cannot be fixed, replacing them with new compatible units is often an easy DIY project. Paying attention to the signs of sensor malfunction and conducting routine maintenance can help ensure your garage door continues working safely and smoothly.

Sensor Issue Potential Cause Solution
Door refuses to close Obstruction in sensor path, misalignment, dead battery Clear debris blocking sensors, realign, replace battery
Door closes unexpectedly Dirty lenses, damage, wires disconnected Clean sensors, check for damage, verify wiring
No sensor LED lights Burned out LED or bulb, power failure Replace sensor unit(s), check power to sensors
Intermittent sensor function Moisture, loose wires, malfunction Seal sensors, check connections, replace damaged part(s)