Hyundai Repair: Transmission problem 1997 Hyundai Elantra, hyundai elantra, emergency flashers

Question
Transmission problem
1997 Hyundai Elantra 4 cyl Front Wheel Drive Automatic 13400 miles

The other day while driving my Elantra, I started to hear a whining noise. Shortly thereafter, my car went into 2nd gear, and then into neutral. I pulled over, turned the car off, waited a few seconds, and then started it up again. The car then worked again and shifted normally. After a few minutes, it went into neutral again.

I drove it to the repair shop (pulling over and re-starting it multiple time). The "check engine" light never came on. The shop said there were no error codes and that it needed a new (rebuilt) transmission.

Since it is an old car, I didn't feel the repair was warranted. While I was driving the car home, it again went into neutral, but then proceeded to shut itself down. The engine stopped, the lights went out, etc. I tried to restarting it, but nothing happened. The emergency flashers wouldn't even work. I was unable to even get it out of Park. I ended up pushing the "override" button next to the shifter to get it into neutral so I could pull it home.

Could the problem be with the computer and not the transmission? The shop thought that this was a separate (additional) problem. PS. The transmission had been replaced 4 years ago with 109,000 miles on it.

Answer
I tend to agree with the shop.  The shut-down of the engine sounds like an electrical issue.  If it were mechanical, the shifter and flashers should have still operated normally.  The transmission issue sounds consistent with a major internal failure because it seems temperature dependent.  In addition, no electrical system issue should cause the transmission to go into neutral; the system is specifically designed so that a complete lack of electrical power to the transmission and control module will cause the transmission to operate in third gear.