Apple Hardware Test Failure Code:4SNS/1/40000000:TGOP-82.125

What is the 820 number of your logic board? 820-3332 or 820-3787? It will be written on the board.

A few potential issues here.

a) Your machine is actually overheating because it is filled with dust. All Apple laptops and iMacs are designed in a way that allows dust to enter, but not to escape. Every machine on earth will eventually get clogged with dust, but Apples far worse than a Thinkpad for example. The retina is really really bad with it. Open it up and clean it, I am sure there will be a mountain of crap in there if this is the 2012 model.

b) On 820-3332 board, tin whiskers growing on Q5501 and Q5503 on the motherboard. If it is not actually overheating, it could think it is overheating due to sensor flaw, and tin whsikers on those are not uncommon. Check U5550 area as well.

My guess is on dust. Blow out the dust, clean up the fans, and you should be good to go. Extra points if you replace Apple's junk shin etsu thermal paste with some Tuniq TX-4, this will go back to being a beast in no time.

Good luck!