Garage door sensor has no light, or a yellow one?

Start with what the lights mean. On many Chamberlain and LiftMaster setups, the sending eye has an amber or yellow light, and the receiving eye has a green one. So a yellow light is often normal for that sensor. What is not normal is a missing light on either eye, a light that is dimmer than its partner, or a color that does not match your manual.

A sensor with no light almost always comes down to power. The sensors get low-voltage current from two thin wires that run to the back of the opener, and that wire can be damaged in many ways: a staple through the insulation, a rodent, a nick from a ladder, or old wire that has become brittle with heat and cold. If only one eye is dark, the break is on that side. If both are dark, the problem is at the opener terminals or the board.

Terminals loosen over time, and moisture can corrode the connection where wire meets screw. A sensor can also fail on its own, especially an older unit. Wire polarity matters too: some sensors have one wire marked with a stripe, and crossing them leaves the eye dark. This is why we test with a meter instead of guessing.

Sensors and wire are routine replacements, not a reason to replace a door or opener. If the opener board is the cause, see garage door opener repair before assuming you need a new unit.