I have the same issue as many others have with "Reduced Engine Power" issues on my 03 CTS. I ordered the Engine Wiring Harness that fixes the issue but I cannot find a guide anywhere to installing it. Does anyone have a link or a walkthrough on how to replace the Engine wiring harness?

 

Anyone out there have any knowledge of this?

 

I have the same problem with my 03' CTS. Where did ya get the harness from? I put a new throttle body on for the same errors as you, bbut that did not help. Keep me posted.