I feel like this has to be a common issue, but I'm having trouble finding references here. It's the same sort of Craftsman garage door opener that most of suburbia has here in the United States. This morning, I found the garage door open after my wife left in the morning, and I found that it was because the door is currently closing all of the way, then re-opening. I went through the standard steps of checking for obstructions (none, although I sweeped the area to be sure) and adjusting the downwards force up, but found that that value was already close to the max, and moving it that small amount more did not fix the problem (I did verify that reducing the force resulted in the garage door not closing all of the way). I furthermore tried the step of reducing the tension on the cable by adjusting the nuts (it seemed like a reasonable thing to try), but no dice.
The weather is cold and wet here, but no more than usual. There is some squealing when the door rises or closes, despite me re-dosing the railings with WD-40. The garage door and opener are probably pretty old, because I got them with the house six years ago, and the impression I got of the owner (now deceased) was that he didn't replace anything until he really had to.
Right now, I have the trolley disengaged so that I can get the door closed, but I'd prefer to fix this before my wife gets home tonight because I can very much see her hitting the button and just continuing on into the door.