Code P1635

I have a 2002 Trailblazer LTZ with 59k miles. The other day there was a loss of power (hp) and the SES and reduced power light came on. I parked it for about an hour and then it drove fine although the SES light was still on. I had the code read and engine light reset by a friend. The code was a 5 volt reference 1 circuit code. Anybody have any clues what the cause of this is or how to fix it?

Why did you have the code reset?
By doing this you lost some valuable information to aid with diagnosis.
The sensors on your vehicle run on a 5 volt reference and the PCM looks for the return voltage.
Sounds like the 5 volt reference was lost.

I reset the code to turn the check engine light off. The only information the scan tool was able to pull off was the 1635 code. Nothing else was available. The reduced power or engine light has not come back on since. I was just wondering why the code was set and what part may need to be replaced.