I'm pretty sure I know what it means, failing wire on the alt running to the PCM.

But thats not my question, I'm wondering why this code is set to OFF?

In LS1-Edit it shows:
Does Error set SES = OFF
Error Mode = Type X = turned off

I've gone back and check this setting in my original stock tune that I initally read from my PCM before tuning began, and it had been set 'off' right off of the dealerships lot.

The only reason I know I'm setting the code is becuase the car felt wierd, and I had a friend w/tach2 scan it, Since LS1-Edit can not show pending codes. But to my surprise I had the P1637 sitting there....I had no idea since it didnt bother to trigger the ses light.

How is your P1637 code configured? ...and why would GM decided to not trigger the SES light?

 

Did you ever figure this one out?

I am getting this code but it is not setting the SES off...

 

Most of the tunes I've seen, from the factory this code is set to "no MIL". I have seen some that were set to "no error reported". Dont know if they changed it at some point, havent bother to figure out if its a year thing. Dont know why its set not to turn on the light, other than its not emissions related.
Alot of the tranny codes are set not to flag too. Some do some dont.

 

Looked it up in my helms and it's listed under engine electrical, not engine controls like most of the others. States PCM will not illuminate the MIL. Went to gearchatter and for a 2K also says it won't set the MIL. Some of the AC codes won't throw an SES light either.