I have an overheating problem with my '95 Lumina. After some time of driving the temperature would go up to 3/4. I flushed the radiator, put new coolant and that didn't do anything. Then I put a new temperature sensor and I got all the engine power back. Probably the computer is convinced now that it is actually not overheating . The gage still goes up but comes down again, at least sometimes. Occasionally I also get a Service Engine soon but the Diagnostic System doesn't let me pull any code! Its simply not working. Is the PCM to blame? What can I do?