They both have lights and both lights should be on.
Garage door not closing totally on one sid.
The extension springs are evenly matched and installed to keep the garage door properly aligned so that it runs smoothly throughout the entire length of the track and closes evenly.
There are usually two springs on each side of the garage door to swing it up.
First check the sensor lights.
If you need to change their tensions move them to a new hole.
A roll up door also has springs on each side that is controlled by a pulley.
Springs are one of the main causes of malfunctioning garage doors.
2 the safety sensors for your garage door located near the floor on each side of the garage on the tracks may have become out of alignment.
Check the sensors one on either side of the opening and look for anything that may obstruct them.
If the door stops and reverses near the bottom the problem may lie with the safety sensors.
Your garage door opener may tell you this by showing a blinking light.
Depending on the brand.
There is one on each side of the door.
If one side of the door is not in line with the other the door won t run smoothly in its tracks and when closed one side of the door won t close completely leaving an open gap.
If your door has a gap.
All you will have to do in this case is readjust the sensors to allow the garage door to fully close.