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Toyota Sienna Hesitation

21 messages,  Last post on Nov 03, 2009 at 7:57 AM

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#12 of 21 Re: Hesitation [ateixeira] by wwest Feb 23, 2009 (11:48 am)
Replying to: ateixeira (Feb 23, 2009 9:37 am) No, the delay is the result of either a pending upshift, an upshift in process, or an upshift just having been completed within the past few hundred milliseconds. In that situation the transaxle simply CANNOT support a downshift and so DBW is used to delay the rise in engine torque. The engine torque cannot be allowed to rise until (presumption of engine at/near idle) the ATF gear type oil pump can (re-)pressurize enough ATF to support the next gear change.   To reduce weight, complexity and improve FE the "old" line pressure accumulator was eliminated back in about '98 in order to allow "real-time" control of ATF line pressure. This was primarily the result of the need to provide the extra space needed build more robustness into the Camry transaxle now that it had to serve duty in the upcoming HEAVIER RX300.   But without the accumulator to sustain line pressure the line pressure collapses to near zero with each gear change if/when the engine is idling or nearly so.   Ford has adopted the same ATF "real-time" line pressure control but also adopted a variable displacement ATF oil pump so line pressure recovery can be quick(er) even with the engine idling. That variability also allows them to improve FE to an even greater extend via reducing the pump displacement volume as engine RPM rises.   Ford has a better idea.......sometimes. Replies to this message: ateixeira (Feb 24, 2009 2:08 pm) wwest (Feb 24, 2009 5:05 pm) ather (Mar 08, 2009 5:12 pm)
#13 of 21 Re: 2008 Toyota Sieanna - "The Hesitation" [wwest] by arodory Feb 23, 2009 (4:19 pm)
Replying to: wwest (Feb 23, 2009 11:34 am) Thanks- it started recently and got worst... does that sound right to you?
#14 of 21 Re: Hesitation [wwest] by ateixeira Feb 24, 2009 (2:08 pm)
Replying to: wwest (Feb 23, 2009 11:48 am) Thanks for the detailed write-up.   Most people just look at the number of ratios in an automatic.   I keep telling them the 4EAT in our 2009 Forester is a whole lot more responsive than the 5 speed auto in our Sienna but noone wants to believe me.   I sense that when I go over a speed bump, I let off the gas slowly, it shifts to 4th I think, then I'm back on the gas and it takes an eternity to figure out it should be back in 2nd, 3rd tops.   So basically the Sienna seeks the tallest gear possible to improve FE but cannot conduct multiple shifts back-to-back without a slight delay between each one.   Sound about right? Replies to this message: wwest (Feb 24, 2009 5:05 pm) ather (Mar 08, 2009 5:12 pm)
#15 of 21 Re: Hesitation [ateixeira] by wwest Feb 24, 2009 (5:05 pm)
Replying to: ateixeira (Feb 24, 2009 2:08 pm) Not quite. The problem only arises when the engine is near or at idle and the ATF pressure is being, or has just, "just", been exhausted due to a throttle lift upshift. "Ask" for a downshift for acceleration in the above circumstance and for up to 2 seconds you are left "hanging".   Just as in your "speed bump" example. Replies to this message: ather (Mar 08, 2009 5:12 pm)
#16 of 21 Re: Hesitation [arodory] by kenjomarisca Feb 25, 2009 (8:34 am)
Replying to: arodory (Feb 20, 2009 6:58 pm) i had the same problem for years,including "pinging"when accelerating out of a turn,toyota said i was not using the proper gas octane and that if it's not chevron that usually happens,so i started using only chevron 91 octane but the problem was still there.take note that 2004 and later siennas does not require 91 octane,this is one point to argue with toyta,but anyway there is a recall to adjust the computer settings to correct the engine pinging problem and transmission hesitation problem and siennas are supposed to be covered up to 95,000 miles if i'm not mistaken,search google for toyota "TSB"or toyota service bulletins.i took mine back to dealership and had them reset the computer,now mine accelerates very good and i dont notice the hesitation.
#17 of 21 Re: Hesitation [wwest] by ather Mar 08, 2009 (5:12 pm)
Replying to: wwest (Feb 24, 2009 5:05 pm) I have the same problem with my 2005 XLE. So can it be fixed then? Is there a TSB for this? Thanks
#18 of 21 Re: 2008 Toyota Sieanna - "The Hesitation" [johnsienna] by hewhohesitates Oct 14, 2009 (6:13 pm)
Replying to: johnsienna (May 21, 2008 10:35 pm) Hi John, I first read your post in the spring of 2009 because I was experiencing exactly the same thing with my 2008 Toyota Sienna. The hesitation in shifting at low speeds when accelerating after slowing down to turn a corner occurs intermittently but is quite noticeable. I've been back to the dealer several times, have been in touch with Toyota Canada - (last contact was in May 2009 and still waiting for a cAll back - it's October!). There is a culture of denial around this problem that is unbelievably arrogant. I'm very disappointed with the lack of commitment to customer satisfaction. My advice to anyone looking at the Sienna is ... buy a Honda Odyssey. I sure wish I had.   John - If you - or anyone - are still following this thread, I'd like to hear how your situation is. Thanks. Replies to this message: yatesjo (Oct 15, 2009 10:07 am) ateixeira (Oct 15, 2009 10:30 am) usa09 (Nov 03, 2009 7:57 am)
#19 of 21 Re: 2008 Toyota Sieanna - "The Hesitation" [hewhohesitates] by yatesjo Oct 15, 2009 (10:07 am)
Replying to: hewhohesitates (Oct 14, 2009 6:13 pm) The hesitation coming off of corners is a design issue with the transmission (if it were Microsoft they'd call it a 'feature'). Every Sienna has it and it is not a defective part so the dealer cannot do anything for you. Toyota may re-engineer it in some future model, but don't expect to get the upgrade.   I can reproduce it every time I want to in my van with a hard brake followed by heavy throttle so the behavior cannot even be called intermittent. It is however, very driving style dependent- in my normal driving pattern I rarely see it My advice: brake further back, gently and with an even deceleration in anticipation of the stop so the down shift doesn't occur so close to when you want to hit the gas and the problem will go away (as a bonus your passengers will be more comfortable since they won't be jerked around as much.) Replies to this message: ateixeira (Oct 15, 2009 10:30 am)
#20 of 21 Re: 2008 Toyota Sieanna - "The Hesitation" [yatesjo] by ateixeira Oct 15, 2009 (10:30 am)
Replying to: yatesjo (Oct 15, 2009 10:07 am) I agree and here's how I explained it:   http://townhall-talk.edmunds.com/direct/view/.f169148/7#MSG7
#21 of 21 Re: 2008 Toyota Sienna - "The Hesitation" [hewhohesitates] by usa09 Nov 03, 2009 (7:57 am)
Replying to: hewhohesitates (Oct 14, 2009 6:13 pm) You and "johnsienna" give a very accurate description of the transmission hesitation. This is definitely a problem with the 08. I also owned an 04 Sienna and did not have this problem. This hesitation has become much more noticeable after we reached 20-25k miles. It is intermittent but very noticeable. The dealer said they can not do anything unless there is a TSB. I am adjusting my driving to anticipate when to lighten the foot on the throttle. Hopefully a bigger transmission issue will not develop in the future. I have been happy with the Toyota Sienna otherwise. How this 08 transmission continues to operate and the service provided by Toyota will determine if we stay a Toyota owner in the future.

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