apple hardware test error 4MEM//40000000: 0x82061390 MacBook Pro late 2012

Welcome!

If your computer is truly a "Late 2012," it is a Retina Model and you cannot reseat or replace the RAM. RAM/memory is soldered to the logic board, not slotted as in the non-Retina Mid 2012 MacBook Pros.

However, your equipment line says "15 Inch" and, as there was never a 15" Late 2012 MacBook Pro, there is hope if you have misidentified your model and your RAM is accessible. Please do "About this Mac" to get a positive Identification of your exact model, looking for the sub-model:

If sub-model does NOT say "Retina," you can check the RAM for proper seating and even increase it if you have less than 16GB RAM, all at home.

No Retina models have user-serviceable RAM. Any RAM issues require a logic board replacement.

Hi,

As for reseat memory modules: Remove the memory modules, then reinstall them again.

How to remove or install memory module.

https://support.apple.com/en-us/HT201165

Hi,

It's a Memory error, your memory modules something wrong.

You need to get new memory modules, though before that, try to reseat memory modules if they are installed correctly.

Yup, I forgot to mention, as Allan told if your MacBook Pro is late 2012, memories are soldered on logic board, you need to replace logic board as a whole.