I was putting in a pin in the ECM today and I removed the TCM for easy access to the ECM. After buttoning everything back up, I started off and I had the check engine light, along with "reduced engine power" on the information cluster...

so... I'm thinking I screwed the ECM putting a pin in... called up OnStar and they showed P0700... TCM problem... double checked the connections on the TCM and one MAY have been a little off... started out again, no reduced engine power, but the CEL remained...

A few key cycles later, I'm driving home and it the CEL goes out... call up OnStar, and the P0700 code is gone.

So... my question is this... can a loose connection on the TCM cause the P0700? It seems it went away after simply reseating the connections...

Hopefully that was it...

by the way, I finally found a use for OnStar... give me my codes when I break something... :)

Did you have the key on when you were doing the take out and reinstall listening to the radio or anything?

You know, now that I think about it... maybe... I went by my parents house and they were in and out of the truck, as my dad is fascinated with XM... he may have listened to the radio at some point...

That would explain it then. It threw the code when the key was turned on when it was unhooked.