Question

I have the engine code P0600 on my 2005 Subaru Legacy GT 2.5L, temperature gauge went up to no obvious problems with overheating

Answer 1

This is a communication error code. All of the computers communicate with each other.

To diagnose you need a scan tool. One of the systems has lost the ability to communicate with the other computers.

Answer 2

P0600 SUBARU - Serial Communication Link
Read more: https://www.autocodes.com/p0600_subaru.html