How do I factory reset my Liftmaster keypad?

To factory reset your LiftMaster keypad such as 877MAX or 877LM that mounts outside garage, you need to erase its memory and reprogram it to opener, which restores factory defaults and allows new PIN. LiftMaster keypads do not have dedicated factory reset button, but factory reset is done by clearing opener memory and reprogramming keypad. First, to erase keypad from opener memory, press and hold Learn button on garage door opener motor unit hanging from ceiling for 6 to 10 seconds until LED goes out, which erases all remotes, keypads, and MyQ devices from opener, effectively factory resetting opener's memory of keypads. Next, to reset keypad itself, remove battery from keypad for 30 seconds to clear temporary memory, then reinsert battery. To reprogram keypad after factory reset, press and release Learn button on opener briefly, LED lights steady for 30 seconds, then within 30 seconds go to keypad and enter new 4-digit PIN you want to use and press Enter, holding until opener light blinks or door moves, indicating keypad learned. For keypad alone without erasing all remotes, you can change PIN by entering old PIN, pressing and holding Enter until light blinks, then entering new PIN and pressing Enter. After factory reset, test keypad by entering new PIN and pressing Enter to open and close door. If keypad still fails, it may be damaged and need replacement costing 30 to 60 dollars.