Access Master Garage Door Opener opens by itself

I have 2 garage doors side by side with model 3280 liftmaster door openers. One of the doors began to open randomly/phantom style! After resetting the codes and checking for staples causing malfunction/shorts and replacing the circuit boards in the wall remote, none of which made a difference,I had the dealer come out and change out the entire opener/ wires/ remotes etc. The following day my "other" opener started doing the same thing-opening randomly--something that only the door beside this one was doing before the new opener was installed. This lead me to believe that it might have something to do with the wireless keypad on the exterior of the garage-(which was the only common denominator with the other side-by-side door. The new opener installed was not compatible with the older model so I knew that there was no interference with the signals from the old and new remotes. I put in a new battery and it still opened phantom style- so I would always activate the "lock" feature on the interior wall mount wired remote to make sure that the door would not open--this worked fine, however, it is a pain in the but to have to get out of your vehicle to close the door via the exterior keypad. Finally, I pulled the battery out of the wireless key pad and the garage door never opened randomly again
I tried reprogramming the keypad with other "temporary codes" and it would not allow them to be programmed--this was also an indication that the wireless keypad and the opener were not cooperating--once I replaced my exterior key pad with a new one--the problem of phantom./random openings was solved. Hopefully some garage door people will read this and get some "much needed" knowledge regarding the "Random Garage Door Openings" which I am sure will haunt home owners-but, if you are reading this info--you now know what your options are for saving some $$ as well as your security and sanity...

If you have a 315MHZ LiftMaster Garage door opener do the following:
Follow the purple wire (Antenna) up and you will see a square purple button.
Press and hold the square purple button for ten seconds until the amber led goes out.
Press and release the purple button one time (The amber led will come on solid).
Press and hold the button on the garage door opener remote control for two seconds (The light bulb on the garage door opener will blink and you will hear a click sound the amber led will go off).
to program the wireless keypad do the following:
Press and release the purple button one time (The amber led will come on solid).
Enter a four digit code into the keypad then press and hold the enter button for two seconds (The light bulb on the garage door opener will blink and you will hear a click sound the amber led will go off).

basically,first check and clean the lid switches or sensors and or got broken switch and not on it`s proper position.

Make sure it isn't the wiring to the wall console by removing the connection at terminal #1 on the end of the motor unit. Staples used in installation can cut through the insulation and cause this problem.

Most likely your door sensors are out of alignment. Make sure they are pointed directly at one another.

There are rough service bulbs you can buy at hardware stores. You can also try unplugging the unit and using a small screwdriver pull out on the center contact in the light bulb socket.

The most common cause of this problem is a bad wall control the wiring going to it. You can eliminate both temporarily by removing the wire at terminal 1 on the back of the motor unit. The wiring sometimes is shorted by the staples the installer uses. The wall control gets used a lot.

Anytime a door opens and/or closes by itself I look for a smashed wire between the motor unit and the wall button.

If the wire is smashed the insulation becomes so thin that power will leak thru the insulation and activate the door.

Loosen the staples with a small screwdriver and slide the wire about ½ inch to move any areas of thin insulation away from the staples.

The second thing would be a bad wall button or a remote with a sticking button.
Or a remote in someone’s purse that gets the button pushed by other stuff in the purse.

The test is to disconnect the push button wires at the power unit. If the self operation stops you have located the problem. If you reconnect the wires and disconnect the wire at the wall button this will tell you if the problem is the wire or the button.

what keypad are you using with new opener? Frequency has changed. can't use old one. you probably never needed to change things; just needed to follow proper coding procedures.

change the security code in the opener and the remote.
seems like omeone in your are have the same frequency remote.