02-06 Transmission hesitation problems

[drifter]

I just don't see it, niether did the NHTSA when they did an investigation into the transmission issue. There has never been a traffic accident reported blamed on the transmission hesitation that they could find, with all the ES's sold from 2002-2004 (when they did the investigation) you'd think they could have found ONE instance if it were truly dangerous. Anyways mine's still shifting smooth after the update and I'm getting better mileage than ever, but that may be due to my new tires.

Annoying sure, dangerous no. Old argument though.

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Curious, what kind of tires did you put on your car? I'm having the TSIB you mentioned done to my 03 ES300 tomorrow. I'm only slightly optimistic.

[SW03ES]

Michelin MXV4 Plus.

Mine's still shifting good, for the record.

[amf1932]

Michelin MXV4 Plus.

Mine's still shifting good, for the record.

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What happened to the Toyo tires that you were raving about?

[SW03ES]

The raving was short lived. They were smooth and quiet but they didn't stay smooth and quiet after 17k miles or so. Got loud and coarse and the rain and snow traction became pretty bad. The Michelins are better tires, smoother and quieter than the Toyos even when they were new and they've significantly improved my gas mileage.

[steviej]

I am still anticipating your comments on the Michie's snow performance. I'll be patient for the next six months.

steviej

[SW03ES]

Hopefully it'll be that long before we have snow lol

[wwest]

Hesitation.........RECAP

It appears that somewhere about the year 2000, possibly earlier, Toyota made a design change in the ECU control firmware for ALL transaxle, FWD, type automatic transmissions. Basically the modification involved upshifting the transaxles to a higher gear, say O/D, or maybe even into neutral, during coastdown circumstances wherein the gas pedal was fully released.

Many owners of the RX300 made note of this aspect, describing it as a feeling of being bumped lightly from behind just before coming to a full stop. At higher coastdown speeds owners described the feeling as the "slingshot effect", the vehicle "apparently" gaining speed upon throttle closure.

It is relatively easy to see that this design change would result in improved fuel economy and lower overall emissions. But if that were the real, or core reason, why not apply the same modification to Toyota's RWD based vehicles?

Why only the FWD or front biased AWD vehicle models?

The only possible answer, seemingly, was to eliminate or substantially reduce the instances of loss of control due to inadvertent, otherwise unavoidable, engine compression braking on, potentially, a very slippery roadbed.

And if you browse about here and there on the internet you will find that many RX300 owners are complaining about premature transaxle failures at 70,000 to 80,000 miles. And there is yet another clue. The owners manual for the RX300 series makes not recommendation for ATF flushing and replenishing for the life of the vehicle.

Yet at 40,000 miles the ATF in my 2001 AWD RX300 smelled burned and looked more brownish than pink. When I enquired of Lexus corporate about this I was informed that the new recommendation was to drain and replenish the ATF each 15,000 miles of standard usage.

WHY?

The hip bone is connected to the leg bone!

Let's assume that I am correct and my RX300 transaxle quickly shifts into O/D, engaging the lockup clutch. Now when I suddenly decide to accelerate the engine will respond to my gas pedal depression INSTANTLY. The O/D lockup clutch is clearly not designed to withstand strong engine torque, nor is likely the 4th, O/D, clutches within the transaxle.

So the transaxle must now be downshifted into the proper gear for acceleration given the current roadspeed, and QUICKLY before the engine starts delivering a really serious level of torque.

But the problem is that with the transaxle being configured for coastdown mode with the ECU having commanded LOW transaxle hydraulic pressure and with the engine at low RPM there is insufficient pressure to fully engage the new downshift clutches fully and quickly.

So the RX300 transaxle clutches SLIP for a few milliseconds during each of these "unexpected" downshifts. Slipping clutches generate lots of HEAT and frictional surface wear beyond that planned during the design phase.

Upon reading some of the posts from owners I have come to suspect that Toyota has instituted an "unspoken" warranty program for otherwise out of warranty transaxle owners with premature failures.

So what does Toyota do about these premature transaxle failures?

Basically NOTHING!

Except for future models.

Those get an e-throttle which allows the engineers to delay the onset of engine torque developement long enough for the hydraulic pressure to rise substantially and thereby fully and firmly engage the "downshift" clutches.

Why not just eliminate or delay the upshifting?

CAFE & CARB regulations.

Or

The automotive insurance industry has picked up on the fact that FWD vehicles have a significantly higher accident and injury rate during adverse weather conditions that their RWD brotheren.

Regardless it has now become pretty obvious that there is no going back insofar as eliminating coastdown upshifts are concerned.

And please remember that Toyota is now on record saying that the hesitation symptom is a result of the need to protect the drivetrain.

[SW03ES]

But again, you see the hesitatation on the RWD cars also, as far back as 1998.

[wwest]

Actually my only real complaint about the 2000 MY GS300 we owned briefly was the SURGE you got with just a slight bit of throttle application. It was especially sensitive, no way to avoid head-snapping acceleration, when starting up from a full stop.

After taking up all the backlash I could from the throttle cable I took it in to Lexus where the service manager INSISTED that my car had an e-throttle.

Have you seen anything close to the number of complaints of hesitation with RWD as we seem to be seeing with just the FWD Toyota/Lexus marques?

[SW03ES]

It actually had both a throttle cable and an electronic throttle, so did the 98-00 LS400. That surging is a symptom of the same issue just presented with a RWD drivetrain.

No you don't see the number of complaints as you do with the FWD cars, but theres a lot of reasons for that. One, there are FAR more ES and RX vehicles sold every year than GS, LS, SC, and IS models combined. You also have an added bias that the attention paid to the issue here on the ES and RX board shows up in google driving ES and RX owners to the site to post their complaints. You can't use the number of members on the site with the issue as a cross section of all the Lexus owners.

If you run a search you'll find threads in every forum about the transmission hesitation.

[wwest]

My searches, google, etc, seem to turn you a predominance of transaxle downshift caused hesitation complaints across multiple marques vs VERY few RWD transmissions.

Can you refer me to a few?

[SW03ES]

I mean search this site.

LS400/LS430-

http://us.lexusownersclub.com/forums/index...3&hl=hesitation

http://us.lexusownersclub.com/forums/index...7&hl=hesitation

http://us.lexusownersclub.com/forums/index...1&hl=hesitation

http://us.lexusownersclub.com/forums/index...6&hl=hesitation

http://us.lexusownersclub.com/forums/index...4&hl=hesitation

And more.

GS-

http://us.lexusownersclub.com/forums/index...0&hl=hesitation

http://us.lexusownersclub.com/forums/index...1&hl=hesitation

http://us.lexusownersclub.com/forums/index...1&hl=hesitation

http://us.lexusownersclub.com/forums/index...0&hl=hesitation

And more.

I've done this for you before...

[wwest]

THis may be helpful here..........

Someone on another thread asked why their Lexus feels like the cruise control is "punching it", when only a small increment in roadspeed needs to be regained.

"Punching it...."

Remember that the automatic transmission/transaxle is heavily biased toward wanting to be in O/D, with the lockup clutch engaged, in order to achieve the best possible fuel economy.

If any level of additional torque is required of the drivetrain the lockup clutch must be quickly released in order to bring the torque multiplication aspect of the torque converter into play. And again, to help achieve the best fuel economy under acceleration.

So even the slightest additional throttle opening will often result in the transmission/transaxle ECU commanding a downshift out of O/D.

Also keep in mind that even absent being in O/D modern day engines are running right on the "cusp", the leanest fuel/air mixture ratio possible using the downstream oxygen sensor for long term, slow reacting, feedback and the engine knock sensors for instantaneous feedback when the mixture gets too lean, the timing too early, or the engine is "lugging".

Engine knock or pinging can pretty severely damage an engine if not quickly corrected or if allowed to often occur even on an intermittent basis.

Engines knock or ping because the fuel/air mixture "flamefront" is expanding too rapidly for the cylinder volume or in the alternative the piston itself cannot move downward as fast as possible to accomodate the rapidly expanding flamefront.

The latter is typically the result of "lugging" the engine.

Most of us who often/still drive stick shifts know by experience and instinct to downshift a manual transmission before we get into the "lugging" range of the engine.

But what about modern day automatic transaxles/transmissions...??

They LEARN.

Over time, as you drive the car, the engine/transmissaxle ECU will build a "map" of parameters which it then uses to avoid engine operational circumstances that are detrimental. The ECU literally "wants" to achieve the absolute best in fuel economy but not at the detriment of mechanical failure of the drivetrain, short (knock/pinging) or long (transmissaxle clutch wear) term.

Think about what happens if you fuel a car that requires premium fuel with regular. The ECU detects pinging in some areas of the previously learned and stored parametric mapping and adusts, accordingly, the operational charactoristics, parameter mapping, of the engine ignition timing, Fuel/air mixture vs RPM & loading, and transmission shift points.

But that's the simple part...

How does it know to re-adjust all of those parameters once you refuel with premium?

Because it pushes the fuel economy "envelope", continuously!

In order to continuously, ALWAYS, operate with the very best parametric mapping for the best fuel economy it continues to "experiment" with the parameters. So, not long after you refuel with preimum "it" will have discovered that the previous, more conservative parameters are no longer valid and build a new set.

[monarch]

In the past month I've rented the following vehicles while on business trips. Since all were 2005 models I assume all had electronic throttles:

1) Ford Freestyle AWD SUV, CVT Transmission: No noticable hesitation

2) Subaru Outback AWD Wagon, 5 speed automatic: Highly noticable hesitation

3) Chevy Malibu FWD 4 speed automatic: No noticable hestitation

4) Chevy Cobalt FWD 4 speed automatic: No noticable hesitation

I think "noticable" may be the key factor here; i.e. all the cars above technically may hesistate, but the amount of the hesitation was noticable and distracting on only one of them.

[wwest]

And yet another clue...

It has bothered me a bit that Toyota and Lexus are recommending that premium fuel will alleviate some of the problems of engine hesitation. Even more bothersome is the fact that some posters have stated that going to premium fuel was helpful in alleviating the symptoms.

WHY?

So I first went to my 2001 RX300 shop manual to read up on the knock sensor and how it was used. Other than the obvious I found no new information there.

But the knot on my head was still festering and I couldn't stop scratching it.

So yesterday out of curiosity I dug into the 2004 RX330 shop manuals regarding the use of the knock sensor.

Surprise...!

My RX300 uses a RESONANT knock sensor and the RX330 uses a NON-RESONANT knock sensor.

The difference??

The resonant knock sensor in my RX300 has a fairly narrow response bandwidth and due to its resonant charactoristics cannot easily be used to discern a fairly light, non-serious, engine knock or ping from a more heavy knock/ping that can quickly result in serious engine damage.

On the other hand the RX330's non-resonant sensor can be used to sense a wide bandwidth of engine knock/ping "sounds" and can readily discern light levels of knock/ping from more serious ones.

What this means is that the RX330's engine/transaxle ECU can "push" the fuel/air mixture ratio "envelope" even further into the regions of engine knock resulting from a "leaner" mixture without unduly incurring potential engine damage. The ECU can "trial run" various lean mixture ratios at all ranges of engine RPM and loading and detect the onset of engine knock/ping before the knock/pinging level

is serious.

The RESONANT sensor in my RX300 is like a stall warning in an airplane, no indication of just how serious the situation really is, might be.

So the newer Toyota/Lexus models equipped with the non-resonant sensor would be able to operate the engine throughout its full RPM and loading ranges much, much closer to the "twilight zone", area of potential damage from predetonation, than would my RX300.

That would, or course, result in the need for greater care, resolution and sensitivity, in selecting the proper gear ratio for a given throttle position commanded by the gas pedal.

[monarch]

wwest, if you want to learn the intimate details about the electronics and engineering of Toyota transmissions and other components you can find it in the official Toyota / Lexus Technician Training Manuals available for download at http://techinfo.toyota.com/

http://i5.photobucket.com/albums/y189/mastertech/tech.jpg

[wwest]

Actually I signed up for that when it first became available but quickly discovered that they don't have anything like "theory of operation" pertaining to their own unique design aspects. Everything otherwise is available in the model specific shop manuals I purchase whenever I buy a new Toyota or Lexus.

[monarch]

While the manuals may not cover "unique design aspects" they do cover general theory of operation in great detail. Like here is just one of dozen of pages that covers the Variable Valve Timing with Intelligence system

http://i5.photobucket.com/albums/y189/mastertech/techa.jpg

[wwest]

Can some one who is really, REALLY encountering this problem do me a favor?

Each night for say a week or ten days disconnect the battery for about 10 or 15 minutes.

The engine/transaxle ECU will be forced to revert to the default factory parameters for fuel mixture and that may eliminate the engine hesitation symptom. At least until the ECU can re-learn just how much it can lean out the mixture before the onset of knocking/pinging and I doubt that one day would be enough.

You don't suppose that's what the dealers do each night so new customers never encounter the symptom??

[SW03ES]

You don't suppose that's what the dealers do each night so new customers never encounter the symptom??

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On a lot of 250 cars?

I seriously doubt it.

[wwest]

They would not have to worry about the new, factory fresh non-driven cars, only the demos, or ones that have been driven enough for the ECU to have "learned" how lean the mixture can be throughout the engine's RPM and loading parameters.

[steviej]

If I can achieve the same thing by just pulling the ECU fuse, then I might try it.

Disconnecting the battery means I loose all my radio and seat presets everytime.

On second thought, won't the result of the first ECU reset be the same as the 10th ECU reset. It always goes back to default, so whatever it learns, it loses.

steviej

[wwest]

I would assume that during the day following each disconnect the ECU will be "busy" re-learning the engine/transaxle parametric mapping. So the "safe" thing to do insofar as this test is concerned is to "reset" to the factory default parameters each night.

[SW03ES]

Just for the record, I was behind a gentleman today picking his 04 LS430 up after having the tranny reflash to help his hesitation problem when I dropped my ES off for service today.

[wwest]

Does anyone have the sequential shift system and is experiencing the hesitation symptom?

If so can you try an experiment for us?

Do a couple of downshift "nudges" of the sequential shifter when you know you might, may, encounter an acceleration recovery problem, hesitation, from an inadvertent upshift during coastdown.

I can't do that myself because the only downshift I can command is all the way down to 2nd.