Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!





Toyota/Lexus transaxle shift delay

MrShift@EdmundsMrShift@Edmunds Posts: 43,647
edited March 21 in Toyota
This topic is more of a technical focus on the causes, characteristics, and speculative solutions to peculiar shifting behavior noted by some of our members in a range of Toyota/Lexus vehicles, various years, various engines. it is open to owners and non-owners.
«13456714

Comments

  • scoti1scoti1 Posts: 676
    Thanks Shifty. I think the title fits better than the one for the former site (Engine Hesitation).
  • the title was wwest's suggestion.
  • user777user777 Posts: 3,341
    thank you wwest and shifty. beggars can't be choosey, but the implication is that there is a transaxle shift delay at root cause, when *it's possible* the transaxle (and by implication transmission) may be doing all that is asked of it, and in a timely manner too on vehicles without the behaviors.

    one would think the word transaxial is perhaps unnecessary and possibly misleading.

    my sincerest thanks shifty that you leave a place open for honest open discussion on this issue.
  • wwestwwest Posts: 10,706
    I keep wondering if it isn't altogether a personal driving style unique to just a few individuals.

    For instance during coastdown does it upshift due to gas pedal fully released, or does it only upshift if the driver hesitates, only briefly or momentarily, in an intermediate position? Say somewhere between the prior "acceleration" position and the throttle fully closed gas pedal position.

    Some of this might even have to do with how often the ECU reads the gas pedal position. Remember that it must make two readings (redundant feedback sensors) virtually simultaneously and cross check the two to verify validity of the position. And what happens if the gas pedal is in motion, moved, between the two readings?

    In any case if I'm the driver and I simply release gas pedal pressure slightly I would fully expect the result to be an upshift, absolutely an appropriate reaction to my input.

    On the other hand if I release the gas pedal from an accelerating position to fully released, QUICKLY, I would expect the ECU to determine that I want "full" coastdown mode using engine compression braking in the current "low" gear.

    (The above theory is quite thoroughly "muddied", of course, by my FWD "safety" theory wherein engine compression braking should never be used.)

    But let's go forward with the thought that we happen to have a driver that hesitates, is hesitant, in changing gas pedal positions.

    Once the transaxle upshifts into an inappropriate gear ratio for even slight acceleration, only quick, rapid, and CERTAIN repositioning, any position, of the gas pedal and HOLDING that position will suffice.
  • wwestwwest Posts: 10,706
    Out driving tonight, out to dinner, and tried to see just what causes my 2001 RX300 to upshift during coastdown. Discovered I really can't feel the upshift well enough to judge whether any specific gas pedal position is the trigger or not.

    But that got me to thinking.

    For eons upon eons (making a point) the springs used to return the throttle butterfly valve to fully closed had to be quite strong and heavy. If you took your foot off the gas pedal the last thing the manufacturer wanted to have happen was the throttle valve getting stuck open due to a slight cable bind or maybe a wee bit of debris in the way.

    But that throttle valve return spring, even if still required, no longer serves to also return the gas pedal to the neutral position. Nor does it provide back-pressure against your foot as you apply gas.

    So, with Toyota's implementation of DBW, just how strong is the spring that provides back-pressure against your foot?

    For those of you with Toyota DBW, is it easier to leave the gas pedal slightly applied due to a weaker spring when your real intent is to fully release it?

    WOW...

    Remember the few discussions/rumors early on about left foot braking might be a cause? If you brake with your left foot then might you "rest" your right foot on the gas pedal? A DBW gas pedal with a very light back pressure return spring....

    Okay, say you were to do that somewhat consistently, rest your right foot on the gas pedal while applying the brakes with your left foot.

    Wouldn't the "learning" algorithm of the engine/Transaxle ECU be perfectly justified in recalibrating the gas pedal neutral position as the one slightly "in" due to foot pressure. Remember the brakes are being applied, why would the ECU "expect" the gas pedal to be anywhere but in the neutral position during braking?

    Anyone want to try a strong, really STRONG, return spring on your DBW gas pedal?
  • wwestwwest Posts: 10,706
    "...The strong braking force does not interfere with the braking force control of the VSC system by turning off the accel. and reducing changes in the driving torque at shift-down...."

    RX330 2004 Electrical System Diagram Pub No EWD563U page 177.

    As of 2004 it appears that there was/is only one "module", "Skin Control ECU with actuator" controlling all VSC functions, including ABS & Trac.

    The above sentence is under:

    4. Mutual System Control.

    Amongst other things does that senstence mean that the engine throttle might be opened in certain situations to prevent engine compression braking from over-coming ABS brake release, moderation, functionality in lower gears?
  • wwestwwest Posts: 10,706
    "...accel..." in the quoted statement refers to the accelerator pedal.

    Apparently the signal from the "Accel Position Sensor" is ignored if the VSC/Trac/ABS module has to take control of the throttle valve position.

    That would certainly help to explain why the vehicle will not accelerate into a tight turn. But might it also help to explain the hesitation symptom?

    Page 148 of the same manual...

    "...It makes smooth driving possible by shift selection for each gear which is the most appropriate to the driving conditions at that time, by preventing dowing (sp? "downing"), squat and gear shift shock when starting off...."
  • wwestwwest Posts: 10,706
    Worth a try.........??

    For those of you having hesitation problems you might try applying a (VERY) light touch with your left foot to the brake in instances where you foresee the possibility of a quick return to "acceleration" mode.

    The 2004 RX330 Lexus shop manual indicates that the transaxle will drop out of O/D the instant the brakes are applied. So just maybe it might prevent the upshifting of the transaxle during brief periods of coastdown.

    The engine/transaxle ECU firmware appears to be sensing that the driver wishes to go into cruise mode when the gas pedal is released or slightly released (coastdown..) and therefore it quickly upshifts to attain the best fuel economy.

    If instead you "apply" the brakes the ECU firmware is more likely to assume your wish is NOT to enter cruise mode but to slow the vehicle. It might therefore leave you in the current gear or maybe even downshift.
  • wwestwwest Posts: 10,706
    Proposal for an aftermarket device to fix hesitation problems in all Toyota/Lexus 5-speed transaxles.

    Constantly monitor the gas pedal position via the OEM hall effect sensors. If/when the gas pedal returns to the "neutral' position check to see which gear the transaxle is currently in and automatically change the "shifter" electrical gear control contacts (there is no mechanical connection) to "command" a one-level downshift.

    If the brakes are applied simultaneously with the gas pedal being returned to neutral then "command" a downshift all the way into first. The vehicle will not downshift until the appropriate lower speed is reached.

    In both cases while the transaxle may not actually downshift due to roadspeed being too high it certainly would not upshift and later leave you waiting 2 to 3 seconds for it to downshift back into the most appropriate gear ratio for the acceleration level dictated by the new gas pedal position.

    If these were RWD vehicles I wouldn't hesitate to bring such a product to market but with FWD we would be incurring the liability that arises from FIRM engine compression braking on the front wheels.
  • After reading the glowing reviews of the Highlander, I'm crushed to hear of the transaxle shift problem. Is this an issue with all/most Highlanders and Toyota vehicles? Seems awful to have a chronic problem that is both annoying and hazardous. It appears that some of you have given this problem a lot of thought and have searched for a solution. Any advice would be appreciated. Should we look elsewhere, or is it something that has been addressed in the '06 models?
  • billranbillran Posts: 113
    Hi clover,

    For what it is worth, I have an 05 V6 AWD Highlander that drives perfectly, with no hesitation problems at all. I have two coworkers who also have that car (04 and 05) and have no problems at all, and love their cars as well. You will find many, many very satisfied owners who love their cars, like we do. There are two million cars on the road with the V6 5 speed drivetrain and those who actually report a problem are a very small minority.

    Also, you should be aware that the majority of the posts about this issue are by people who don't actually own one of these cars and have never personally driven one to experience the hesitation first hand. They enjoy speculating about the issue and are mostly well intentioned, but it is all based on second hand information.

    And finally, there are also some posters with an obvious anti-Toyota agenda who may provide you information that is not exactly unbiased.

    With that in mind, I personally think you should still give the Highlander a close look with an open mind, I love mine!

    Good Luck
  • scoti1scoti1 Posts: 676
    There have been reports of hesitation in 2006 models, so I can tell you that it does not appear that the problem has been completely fixed. However, this problem does not seem to be noticeable in every vehicle. Even when it is noticeable, it seems to be present in different levels of severity, so it can range from "no problem" and "minor annoyance" to "serious problem" based on my experience and the reports I have read. If this is the vehicle you really want, I would just recommend that you take several of them on lengthy test drives in different driving conditions. Read through these boards, other web site discussions, and the TSB issued by Toyota so you can get a better handle on when people notice the problem the most and try to replicate those driving conditions.
  • user777user777 Posts: 3,341
    agreed. good advice -> clover2 should look at the TSB and see if the hesitation is evident in any of those scenarios, test driving another if it is.

    this is a problematic post though:
    frogg, "Toyota Highlander Owners: Problems & Solutions" #3294, 11 Jan 2006 9:20 am

    there was at least another post in the forum that was shut down where an owner didn't experience the issue at the time of purchase. perhaps he/she wasn't being sensitive to it while being distracted by being in a new vehicle, etc, etc. that's a possibility.
  • Hmmm...I read that post carefully and it sounds different than the usual complaint...there was a definite "slip" in the transmission, as in revving in neutral, according to that poster.
  • user777user777 Posts: 3,341
    Good point, yeah slipping between gears. Very odd and not the same issue as other people reporting hesitation. One interesting thing was that it initially drove fine, got bad, was reset and got bad again. I do believe there are potentially a few issues, some the TSB addresses, and some that are not. Interestingly they changed out his valve body (would that include or not include the solenoids?). It wouldn't surprise me if his problem is very very different from the rest of the posters, which is what I think you are implying may be the case. i'm wondering why the service manager didn't replace his TCM to see if that was at root cause.
  • scoti1scoti1 Posts: 676
    In his title, frogg mentions hesitation and shifting problems. Hard to tell by hsi description, though. The tech mentioned the "slipping".
  • user777user777 Posts: 3,341
    right, and to be fair to posters like billran and others, no doubt there are some people that would classify or categorize the problem(s) using similar terminology, in part because these systems are complex and our understanding of what is actually happening isn't widely known...for that matter, even by the service techs apparently.

    this is why it is so important for someone to capture objective data that we could graph and review sequence of events to get a better handle on what is being commanded and when, and what is the response and how much later.

    i thought the other day of going down to a dealership and driving one of the vehicles in question to see for myself if i instantly noticed a problem, or could get the vehicle to exhibit the behavior. i just don't want to lie to one of the sales reps about why i want to take the vehicle for a spin. if i were looking for a vehicle for purchase, i would.

    too bad we couldn't get some posters shopping for cars to do some helpful "lifting".
  • wwestwwest Posts: 10,706
    seems to run through some of the complaints of engine/throttle hesitation, so maybe it's a not so common aspect of a not so common engine/throttle hesitation.
  • wwestwwest Posts: 10,706
    Several years ago TeamSeattle(.com) ran two Saleen SR-7s at the 24 Hours of Daytona. Prior to the race one of the cars had been over-heating and had to be torn down to replace both radiators.

    Just before race time, really too close for comfort, the car was finally re-assembled and when the engine was started it immediately went WOT and luckily was shut down before anything was damaged.

    For some reason the engine control ECU had "forgotten" the parameters for the DBW gas pedal/throttle control system.

    Picture this....

    A technician laying upside down, butt on the drivers seat, head and shoulders in the brake/clutch/gas pedal "tunnel". At the same time the Saleen factory engineer, white shirt and tie, is standing behind the cab with one foot on each exhaust manifold of the big-iron Ford V8, laptop computer laying on the cab top in front of him.

    The Saleen engineer has the technician alternate the gas pedal position between "neutral" and WOT while he manually moves the throttle itself to the same, appropriate positions, meantime using the laptop to "tell" the Saleen's engine ECU to "trap" the sensor signals to save the positional parameters to coordinate the throttle valve position with the gas pedal.

    Often wished I had made a video of the procedure.

    So, how does your car "learn" these DBW parameters, for learn it must. And does it continuously re-adjust those parameters from time to time if it decides the previous parameters are for some reason no longer valid? Floor mat laying lightly on the gas pedal for instance.

    Or someone left foot braking???

    I can imagine a VERY confused engine/transaxle control ECU should the gas pedal suddenly go "negative" from the previously memorized neutral position established while that floor mat was in place and now removed or someone's right foot being finally removed from the gas pedal after "resting" there even with the brakes applied.

    I have no doubt that the previous "false" neutral gas pedal sensor parameter would be immediately scrubbed, erased, but how long would it take, and HOW would it, go about re-establish a "certain", for sure, neutral position parameter?

    And just how would the transaxle "act" until a new gas pedal neutral position parameter is memorized?
  • user777user777 Posts: 3,341
    I can imagine a VERY confused engine/transaxle control ECU should the gas pedal suddenly go "negative" from the previously memorized neutral position established while that floor mat was in place and now removed or someone's right foot being finally removed from the gas pedal after "resting" there even with the brakes applied.

    I have no doubt that the previous "false" neutral gas pedal sensor parameter would be immediately scrubbed, erased, but how long would it take, and HOW would it, go about re-establish a "certain", for sure, neutral position parameter?


    there you go. many moons ago, i suggested maybe we were dealing with a non-linearity in the accelerator or throttle position sensors. of course, they could be loosing their calibration due to mechanical slop or similar.
«13456714
This discussion has been closed.