Audio not showing up, SMC Fault PFM006 - Possibly palm rest sensor

I've got a great deal on a MacBook from early 2015 for 100 euro. From the outside, the machine looks brand new; white keyboard lighting, matte keycaps and no scratches or dents at all.

There is something wrong with the audio; Built-in Speakers, headphones and Built-in Microphone do not show up in macOS. Even in when reinstalling macOS. Also, there is no boot chime or sound when connecting the charger, which led me to believe that this is most likely not a software problem.

Also, FaceTime is getting a Temperature warning, most likely because of the high reading of the palm rest temperature sensor.

I ran trough Diagnostics, which returned:

• PFM006 - SMC Fault
• PPN001 - Power Management System Fault

It looks like TG Pro is getting normal temp readings, they are all updating nicely and they all make sense. But there is one sensor that i think might be faulty, the palm rest temperature sensor. It’s giving a constant reading of 50 degrees celsius, without any fluctuations. Even when i let the MacBook sit, powered down for a couple of hours, it will always return 50 degrees, which is abnormally hot.

UPDATE 24-06-2023 18:32
It looks like TG Pro shows a sensor that this MacBook simply does not have (palm rest sensor). I've tried another open source program (GitHub) which talks directly to the SMC, which is stating that the palm rest sensor functions normally. This program also shows two sensors that are not included in this line of MacBooks, the Memory Proximity- and RIO-sensors. Also, every post i came across, showing TG Pro on a MacBook A1534, will always state that the palm rest sensor is at 50 degrees.

END OF UPDATE

I’ve taken the Mac apart. I can see that the battery has been changed at some point. It currently has 31 cycles, the battery doesn’t get hot or anything like that. I’ve tried reseating all ribbon cables from the trackpad, right speaker and audio-jack port, without any success. I also co

uldn’t find any signs of liquid. I believe only the battery was changed since the black tape on the display connector was still stuck firmly to the little connector bracket.

Things i’ve tried so far:

1. Resetting SMC, PRAM multiple times, even after opening the Mac after reseating the ribbons.
2. Tried plugging in a 3,5mm cable, it didn’t show up in macOS.

I don’t know where the palm rest temperature sensor resides, my guess is the trackpad but i don’t know for sure. I simply don’t know what to check, there is almost no info about this Mac online.

Thanks for reading, i hope you guys may help me out.

UPDATE 24-06-2023 23:13
Well, i took the MacBook apart once again and completely disconnected the cable that goes from the logic board to the audio controller. At first glance, everything looks okay but on closer inspection, i could see a small point in the cable. I don't know if this is enough to completely loose connection tough. The audio board itself looks really clean, no burned chips. There is a small white 'sticker' on the board, i suspect it's for liquid detection. it's completely white.

Just to be sure, I've just ordered a new flex cable. Will update again with the results.

UPDATE 03-07-2023 16:01
I received the new audio flex cable today, installed it and started my Mac. It's still the same as before; no audio devices, FaceTime error. Tried multiple SMC and PRAM resets, but still no luck.

I'm about to buy a scrap MacBook with an audio board inside and a clean display for a nice price, going to sell the OEM display to cover the cost of the audio board.