AWD,,comes on in heated day after 25 miles. Never in winter time. It disengage

What is your question?

This occure every time in summer, but never in winter. I can't say, because this is the only time. The fluid get to hot or something. You can drive it the hold winter and it want come on, but as soon as it get warmer outside, it comes on after you drive about 25 miles.

What makes this problem better or worse?

The temperature of the day.

How long has your 2006 Buick Rendezvous had this problem?

Going on three years.