Garage door sensors are wired to the automatic overhead door opener. Contact a professional if troubleshooting or wire replacement does not correct problems with the door closing properly. If the garage door opener is Security+ 2.0, have the customer activate the door to determine if the opener was only in sleep mode. Hold off on replacing the other sensor until you check the wiring.
I have tried troubleshooting my Craftsman door opener (model 139. Only the right side green light will glow, while the left sensor light will not come on. The sensor lights are no longer on and I believe this is causing my problem. While you are waiting for an expert answer, I did manage to find three links that will provide you with some good troubleshooting tips and I am attaching the links below. I myself have a Craftsman automatic opener with sensors that look very much like the ones in the photo below. I put my hand in front of the receiver sensor and confirmed that the light turned off to verify it was functioning properly in case the door encountered an obstruction.
Genie of Fairview provides garage door troubleshooting guides, FAQ’s, and customer support. When the infra-red sensors are malfunctioning, usually one of the sensor lights will be blinking. I have a 1/2 HP Craftsman garage door opener. Garage door won’t close, nothing in the way of the sensors. A repairman had it fixed and was off my property in 7 minutes. I have yellow or orange light on the left side. Currently my garage door opener light will come on if the door is left open and something like a cat or dog walks into or out of the garage. My Craftsman opener had an option to disable the sensor leaving the light on ONLY when the opener was used. Press the Light button to turn the opener light on or off.
Craftsman Garage Door opener sensor light is out. Does this indicate a bad sensor? Door will not c. Both the sending and receiving sensors have a small LED light to help us align and troubleshoot them. Liftmaster Professional, Chamberlain and Craftsman making them similar in many respects.