Two problems related to transmission not engage 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.
The shifter lever made a sound and behaved as if plastic was breaking inside of it. This happened when shifting out of "park", and into gear when the car was stationary. After this, the shifting lever became loose and does not seem to have the tension to "spring" the lever into the appropriate position naturally. For example, normally the shift lever will have tension pushing toward the left so that the shift lever engages park without having to manually press it into place. Now it will float to the right and may not engage into "park" without the driver specifically concentrating on pressing it to the left. This vehicle is current with all of its recalls with the exception of the latest spare tire carrier cable inspection issued in 2014. The specific part that has broken is unknown, but I suspect there is probably a tension spring associated with the shift lever which helps keep it in the desired location which has broken. . Read more...
After years of dealing with this issue Toyota has yet to provide a reason or solution. When traveling at lower speeds the transmission disengages and when you need to accelerate there is a 1 to 2 second delay before the transmission re-engages. Toyota made me service the transmission. . . No help. . . . Then they claimed I needed a software update. . . Which they charged me $80 . . . To update their software design flaw. Still. . . The transmission has not improved. My only concern is that if I should ever need to accelerate to avoid an accident, my van may not respond in time.