2003 Buick Rendezvous Can't get codes

2003 Buick Rendezvous Automatic

I currently am having problems with my vehicle having the check traction system light on (and anti-lock break/traction off). It does not come on directly but does after a little time. My husband has attempted to take my vehicle to AutoZone and to a mechanic )he knows personally) to get the codes read by the machine. For some reason he said we are unable to retrieve the codes. That the hookup has no power. How would I fix this so that I am able to read the codes? How do I make the hookup have power? Thank you!