Sensor Obstruction
Chamberlain Garage Door Opener
Severity:What Does This Error Mean?
A sensor obstruction on a Chamberlain garage door opener means the two photo-eye safety sensors near the floor on each side of the door are not aligned or something is blocking the beam between them. Both sensors must have solid (non-blinking) LEDs for the door to close. Check for objects in the beam path, then adjust sensor brackets until both LEDs are solid.
Affected Models
- Chamberlain B970
- Chamberlain B6765
- Chamberlain myQ series
- LiftMaster 8500 series
- Most Chamberlain and LiftMaster garage door openers
Common Causes
- An object (box, bike, garden tool) blocking the beam between the two sensors
- A sensor was bumped and is now pointing away from its counterpart
- Direct sunlight hitting the receiving sensor, blinding it
- Sensor wire has become loose, frayed, or damaged
- Cobwebs or dirt on the sensor lens
How to Fix It
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Check for any objects between the two sensor units mounted near the floor on each side of the door. Remove anything in the beam path.
The beam travels horizontally at floor level across the full width of the garage door opening. Even a broom handle or a garden hose crossing the path will trigger the obstruction.
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Check both sensor LEDs. The sending sensor (usually has an amber LED) should be a solid light. The receiving sensor (usually has a green LED) should also be a solid light. A blinking LED means misalignment.
If the green receiving sensor is blinking, it is not receiving the beam — loosen its mounting wing nut, adjust the sensor angle until the LED becomes solid, then retighten.
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Wipe both sensor lenses with a dry cloth to remove dust, dirt, or cobwebs.
A dirty lens can scatter the beam enough to trigger the obstruction alert even when nothing is blocking it.
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Check whether direct sunlight is hitting either sensor at certain times of day. If so, shade the sensor with a small piece of cardboard taped above it.
Strong sunlight in the afternoon can overpower the infrared sensor signal and mimic an obstruction. This is a common issue in west-facing garages during summer.
Frequently Asked Questions
Can I bypass the safety sensors to close the door?
Temporarily, yes — hold down the wall button continuously and the door will close while you hold it. This is designed for cases where a sensor has failed. Do not permanently bypass the sensors — they are a safety feature that prevents the door from closing on a person or pet.
How do I know which sensor is the sender and which is the receiver?
The sender has a steady amber (yellow) LED and does not need to be aligned — it just broadcasts the beam. The receiver has a green LED and must be aimed precisely at the sender to receive the beam. Adjust the green-LED sensor when troubleshooting alignment.