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LS460_Downshift/Passing Gear/Kick-Down Hesitation

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Old 02-03-14, 08:50 AM   #1
lucyq
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Post LS460_Downshift/Passing Gear/Kick-Down Hesitation

This Thread is for the following issue: An unacceptable hesitation in transmission downshift/passing gear/kick-down (while the vehicle is in motion). This is an important issue for those who experience it (for example, see the 2 NHTSA complaints from actual LS460 owners below in Footnote 1). It should not be closed as long as LS460 owners experience this issue and desire to learn about how to resolve it.

"Tee" recently closed my proposed thread about this ( http://www.clublexus.com/forums/ls46...esitation.html ), incorrectly stating that "This has been discussed several times over the years, here is the link found in the FAQ sticky located at the top of the LS460 forum. http://www.clublexus.com/forums/ls46...-problems.html ". However, it is clear that the link he provides is for a different thread about poor acceleration from a stop (due to an engine timing issue). (Nospinzone also suggests this topic has been discussed in Club Lexus Forum, but does not provide a link to the thread that he is referring to.)

Please don't close this Thread, as I have not been able to find a Thread on this Club Lexus Forum that specifically addresses the issue I now describe to you:

I have been trying to wrap my head around my 2008 Lexus LS460’s transmission downshift (or “kick-down”) hesitation for some time. Not only does it hesitate to downshift into a lower passing gear, after the downshift and acceleration does occur, when I lift my foot to stop the acceleration after I pass, the transmission remains in the passing gear and hesitates to upshift (leaving the engine revving in the lower gear) for an unacceptable time. It does eventually downshift to a passing gear and upshift out of the passing gear, but it is dangerous. For example, I start crossing into the passing lane in expectation of rapid acceleration, but the car's hesitation to accelerate as expected places me at risk of being hit from behind.

Seeing the NHTSA complaints from other owners [see Footnote 1 below] gives me hope that Lexus has a fix for it. Lexus owners are not the only people who have experienced the same problem. For example, Jay Shoemaker, in his November 13, 2006 article on the Lexus LS460 (titled “Lexus LS 460 Review”), described the delay in downshift as follows: “there's an unacceptable hesitation as the transmission rows through a few gear changes before finding the meaty part of the engine’s torque range” (http://www.thetruthaboutcars.com/2006/11/lexus-ls-460/ ). My take on this “unacceptable hesitation” is it reflects a software programming issue.

Regardless of the number of gears a transmission has, a rapid depression of the accelerator pedal by a given distance (of pedal travel) should cause the computer to rapidly select a gear to downshift to and make it happen quickly (based on the computer program that takes into account the rate of pedal depression, the distance of pedal travel, and the speed of the car). The transmission should downshift to that selected gear almost instantaneously given today’s fast computers, regardless of the power created by the engine (i.e., regardless of what the variable valve timing (VVT) and direct injection (DI) programs are doing).

Has anyone else experienced this downshift hesitation issue? Is there a Lexus Technician out there who can explain why this occurs and how it can be solved? Is there a Service Bulletin with an official fix?

------------------------------------------------
Footnote [1]:

“THE CAR WILL (INTERMITTENTLY) HESITATE TO ACCELERATE. THIS IS ESPECIALLY DANGEROUS WHEN YOU ARE TRYING TO MERGE INTO THE FREEWAY OR SIMILAR OCCASIONS. WHEN ATTEMPTED TO DEPRESS THE GAS PEDAL WITH EXPECTATION THAT THE CAR WILL RESPOND AND ACCELERATE AS NORMAL, THE ENGINE JUST REVS UP AND THE VEHICLE DOESN'T MOVE ANY FASTER THAN CURRENT SPEED. THIS WILL CONTINUE FOR 5-10 SECONDS THEN IT KICKS IN. THIS DELAYS IS VERY DANGEROUS WHEN YOU WANT TO GET OUT OF HARMS WAY (ACCELERATE TO MERGE INTO FREEWAY, PASSING ETC). THE PROBLEM IS INTERMITTENT AND WILL GO AWAY BY ITSELF WITHIN A FEW HUNDRED MILES (BUT WILL COME BACK SPORADICALLY). ALL THIS HAPPENS BY ITSELF AND CANNOT BE REPRODUCE AT WILL” (NHTSA ID Number: 10507520, Date Complaint Filed: 04/08/2013).

“WHEN I NEEDED TO PASS A VEHICLE, I WOULD STEP ON THE GAS (MOST OF THE TIME PUSHING THE ACCELERATOR PEDAL TO THE FLOOR) THE CAR WAS VERY SLUGGISH AND UNRESPONSIVE. IT WOULD TAKE ABOUT 10 SECONDS FOR THE VEHICLE TO SLOWLY ACCELERATE AND THEN THE CAR WOULD TAKE OFF WITH THE RPMS CLIMBING NEAR RED LINE UNTIL I RELEASED MY FOOT OFF THE ACCELERATOR” (NHTSA ID Number: 10506001, Date Complaint Filed: 04/11/2013).
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Last edited by lucyq; 02-03-14 at 08:54 AM.. Reason: I included a NHTSA complaint that does not appear to be relevant
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Old 02-03-14, 09:20 AM   #2
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You know what, I am experiencing the same issues plus some more, let me know if you have any symptoms like mine. Here is the thread I posted up today http://www.clublexus.com/forums/ls46...-problems.html
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Old 03-15-15, 01:18 PM   #3
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Quote:
Originally Posted by Bozookah View Post
You know what, I am experiencing the same issues plus some more, let me know if you have any symptoms like mine. Here is the thread I posted up today http://www.clublexus.com/forums/ls46...-problems.html
If all your suspension and others checks out good, then it's most likely a ecu software issue. Probably needs to update the ecu software or replace.
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Old 03-16-15, 08:36 AM   #4
lucyq
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Default LS460 trans shift hesitation_solution (as of now)

At about 85K miles, I convinced our Lexus service department that they ARE able to change the transmission fluid, which I proved to them by showing them the service procedure (which I found on the internet). Cost me $150 for this. This solved the problem -- what a dramatic difference the transmission fluid change makes!

Problem starting again about 6 months later (don't get me wrong, transmission shifts, and in general performs, like new WHEN IT DOES SHIFT CORRECTLY).

Service department suggested a reflash the ECU, which has worked so far (it has been about 6 months since reflash; car has about 93K miles now).

Cannot tell you if, or when, the shift hesitation will begin again.

Peter.
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Old 03-16-15, 08:36 AM
 
 
 
 
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