Two problems related to transfer case have been reported for the 2004 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Toyota Sienna based on all problems reported for the 2004 Sienna.
Driving in passing lane of interstate 70 mph, very loud crashing noises from undercarriage that continued as long as car was moving forward. Tow truck driver said power train (drive line he called it) had come off. Mechanic identified cause as transfer case seizing up, probably because of some internal part coming loose. Right front wheel also seized up. Damage to van is catastrophic - it's totaled. Miraculously I was able to pull off to shoulder without crashing.
With about 6000 miles showing on the odometer, and children present in the vehicle we suffered from a manufacturing defect; a complete mechanical failure that was life threatening. I was on an on-ramp preparing to enter the freeway when I felt the under carriage of the vehicle slam down. The rear differential disintegrated, and the vehicle was unable to accelerate or be put into gear. With tremendous effort and horrendous noises the vehicle could struggle to move at about 5 mph. Once the dealer received the vehicle the Toyota representative. Appeared within days to inspect, collect, and later analyze the failed parts. The transfer case and rear axel assembly were replaced. We cannot and will not be picking this vehicle up from the dealer due to the unexplained and dangerous events that have occurred.