Rear vent windows not operating properly is a common problem with Honda Odesseys. The solution is to replace the window motors.Google+
Car Problem Reports
Honda Odyssey Rear (vent) Windows Operate Intermittantly, and Eventually Fail
Honda Odyssey Problem
Average Mileage: 109,940 mi (38,700 mi - 168,000 mi)
Visitor, 2000 Honda Odyssey, 168,000 mi
Happens intermittently. If they won't open/close, I try again at a later time and usually the problem is gone. i have had them stuck in open position when a rain storm came through, but the inside didn't get too wet so I really dion't worry about it. Hopefully they will never get permanently stuck in the open position!
Visitor, 2002 Honda Odyssey, 113,000 mi
Both window motors failed.
Rear windows would not always open or close. Dealer said needs new window motors for about $100. plus labor elected not to do had them disconnect window motors with windows in the closed position.
This is a well-known problem with the Odyssey. It happened to me, and I found detailed instructions on repairing the problem on the internet (http://www.odytalk.com/showthread.php?29-How-to-Fix-your-Rear-Vent-Window-Motors&s=b2feb4ba865d367c997ac540399c6788&p=36#post36). I have yet to complete the repair; they've been completely inoperable for four years now... maybe this weekend I'll get to it. ;)