One problem related to transmission not engage has been reported for the 2006 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2006 Toyota Sienna based on all problems reported for the 2006 Sienna.
I was driving on a straight, level dry road with cruise control set at 58mph. Suddenly car began to downshift. Assuming transmission problem I disengaged cruise control and car almost came to a stop. I pushed gas pedal and drove in low gear to nearest pull-off. Discovered left front brake was smoking. After things cooled off I drove car in low gear about 6 miles to local service station. Mechanic found all brakes locked and removed all wheels. He inspected all rotors, calipers brake lines, etc and found no problems. (I had new brakes installed at dealership about 4 months earlier. ) when mechanic manipulated left front caliper all brakes disengaged. Mechanic found brake fluid level was normal. I've driven car about 500 miles since problem occurred with no problems. I don't use cruise control often - and haven't used it since problem occurred. I'm wondering if problem is with cruise control rather than brakes?? this could have been a disaster if it happened on a freeway at higher speeds!.