My 2014 jdm had the same issue and it was the small electric motor inside (total of 3, one for folding and two for the mirror adjust. The brushes had failed.
Was a pretty easy fix, just take your time with the disassembly. The folding motor is inside the black plastic housing on the right side of the first picture.
You have to remove the 3 JIS headed screws and one black one also that is under the aluminium bracket. Only half of the lower plastics come off before removing the hidden screw. Can be opened with a normal PH driver but they are loctited, so careful not to round the heads.
Also the blinker needs to come out and be careful if yours has the heated mirrors, the tiny connectors might be corroded. Just spray some zep or wd40 and wiggle them off with pliers.
Basically when you have everything removed, the plastic housing comes apart with 4 tabs and you have to mind the bunch of wiring when opening it up.
The white plastic ring on the oem motor swaps over and if possible take note of the orientation of the slotted axle, makes it easier to reassemble.
Bought mine from here:
Mirror motors. Chose the cheaper option as the oem was sold out when I bought mine.
Hit me up if you need any other info on this.