A small safety reversing sensor with a glowing LED mounted low on the track beside a closed white garage door

Garage and car

Garage door won't close? Start with the sensors

4 sources

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Quick answer

If the door opens but won't close from the remote, look at the two small sensors near the floor on either side of the door. LiftMaster's manual says that when the beam between them is blocked or misaligned, a closing door reverses, and an open door won't close at all. The LEDs on the sensors tell you which problem you have.

Maker parts (check your opener's manual first):

LiftMaster 041-0136 safety sensor kit Chamberlain 041B0873 sunblocker kit

What the sensor lights mean

Sending sensor is amber, receiving sensor is green, per LiftMaster's manual.

Lights	Meaning (LiftMaster / Chamberlain)	What to do
Both steady (amber and green)	Aligned and wired correctly	Nothing; test the safety system as your manual says
Green blinking	Beam obstructed or sensors misaligned	Clear the path, realign (how)
Either light off	No power to that sensor	Check opener power and the sensor wire

LiftMaster's manual: the sending sensor has the amber LED and the receiving sensor has the green LED. If either LED is off, check that the opener has power, that the sensor wire isn't shorted or broken, and that white wires go to the white terminal and white/black wires to the grey terminal.

Guides in this section

Fix guideSensor blinking greenClear the beam, loosen the wing nut, aim, tighten.Read guide

Fix guideWon't close, light flashesWhat the flashes mean, and the hold-the-button workaround.Read guide

GuideSunlight and sensorsSwap sides, shade the green sensor, or add a sunblocker.Read guide

Never bypass the sensors. LiftMaster's manual says the safety reversing sensor is a required safety device that must not be disabled, and the beam must be no higher than 6 inches above the floor. After any fix, test it: the door must reverse when the beam is blocked.

How we work: sensor details come from LiftMaster's 98022 manual, Chamberlain Group support articles and LiftMaster's sensor kit page. We don't test garage door openers ourselves. Sources are listed below.

Questions people ask

Why won't my garage door close but it opens?

LiftMaster's manual says that if the sensor beam is blocked or misaligned while the door is open, the door won't close.

Which garage door sensor is which?

LiftMaster says the sending sensor has an amber LED and the receiving sensor has a green LED.

How high should garage door sensors be?

LiftMaster's manual says the beam must be no higher than 6 inches above the garage floor.

Sources

Last checked Oct 23, 2026. Details come from LiftMaster's 98022 manual and sensor kit page and Chamberlain Group support. Never disable the sensors; test them after any fix.