One problem related to transmission gear slipping has been reported for the 2005 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2005 Toyota Sienna based on all problems reported for the 2005 Sienna.
As we exited the dealership after purchasing the 2005 Toyota Sienna van, the transmission seemed to slip as it downshifted into a slow turn. This happened so many times with various drivers that we contacted the dealer. Some five trips and weeks without our vehicle, the dealer couldn't fix it. They also experienced the problem and would contact the Toyota rep. More visits and calls and no repair. The dealer said the transmission was getting used to the primary driver. Dealer seemed to doubt our credibility, but has agreed to either fix it or "convince us that this is the way a 2005 Sienna van drives. " after reading the numerous complaints just like ours, I doubt that Toyota can fix this. Computer was reprogrammed and fluid changed--made it worse. We give up. We note that the 2006 Sienna has not received any complaints like this.