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I think the hesitation is a software problem. I bought a 2020 a week ago and there was no hesitation. Last weekend I went to the dealership to inspect a check engine message (it was a defective CO2 sensor).

After the service inspection, the vehicle software appears to be updated (or ECU reset?) because the start/stop feature was enabled (it was always OFF by default and now it is ON by default ?) and I began to feel that engine hesitation at low rolls.

Lets hope there is a new Toyota update or something that fix it. Or “retrain” the vehicle ??‍♂
 

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Yeah, it sounds like they disconnected the battery and reset the ECU and your car has to learn all over again. Somehow, I don't think A.I. is quite ready for prime time in automobiles just yet because it sure seems flaky that either a dead battery or disconnecting it can screw things up again. By the way, someone here posted the Toyota recommended procedure for the tech to follow retrain the trans. programming after doing the TSB and now I can't find it. I'd like to have a copy in case I try to reset my trans ECU by disconnecting the battery so that I can retrain it the way Toyota wants it to be done.
 

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Yeah, it sounds like they disconnected the battery and reset the ECU and your car has to learn all over again.
That's really odd. I've disconnected my battery on purpose when installing my OEM hitch. The battery was disconnected for a few hours. I've also come out to a dead battery in the morning once. Power disconnected twice and I've never had this hesitation issue.
 

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That's really odd. I've disconnected my battery on purpose when installing my OEM hitch. The battery was disconnected for a few hours. I've also come out to a dead battery in the morning once. Power disconnected twice and I've never had this hesitation issue.
I was inquiring from BazingerZ's comment that if disconnecting the battery would cause a reset of the ECU, I could then try driving the car and have it relearn the trans shift points. But pnunez seems to be having new hesitation troubles after his car's battery was disconnected whereas he didn't have it before. I had the TSB done for the second gear downshift hesitation and lurching. That worked fine, but now I have issues with first not downshifting until I'm almost stopped from the day the TSB was done. It's not a substantial issue, just an irritant because most of the time during a rolling stop, it stays in second. So the reprogramming just moved the issue to first on my Rav4 and I don't think any amount of driving relearning will fix that since the base programming for the trans seems to be hard programmed into some sort of flash memory. Otherwise, why bother with the TSB procedure if all it took was to disconnect the battery and drive the car in a certain fashion to fix things? I'm guessing any "learning" is done on top of those base parameters. Inquiring minds would love to know how this system works.
 

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There is software you can use to reset the ECU, but in my experience, disconnecting the battery and connecting the red and black leads together to drain any stored energy in the circuits is enough to clear everything. Then, after reconnecting the battery, you can start training the ECU to idle properly and shift smoothly at various driving conditions. The ones you want to focus are the ones the transmission struggles to shift smoothly. It took me a while to get this right. I tried multiple times(disconnect battery and retrain), but I got it and I was able to get my transmission to shift right after the dealership screwed up my transmission. That was on my 2017 gas RAV4 though.

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I think the hesitation is a software problem. I bought a 2020 a week ago and there was no hesitation. Last weekend I went to the dealership to inspect a check engine message (it was a defective CO2 sensor).

After the service inspection, the vehicle software appears to be updated (or ECU reset?) because the start/stop feature was enabled (it was always OFF by default and now it is ON by default ?) and I began to feel that engine hesitation at low rolls.

Lets hope there is a new Toyota update or something that fix it. Or “retrain” the vehicle ??‍♂
This doesnt make sense. I thought all 2020s had auto start stop by default. ??

So you should have had it when you bought it.
 

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By the way, someone here posted the Toyota recommended procedure for the tech to follow retrain the trans. programming after doing the TSB and now I can't find it. I'd like to have a copy in case I try to reset my trans ECU by disconnecting the battery so that I can retrain it the way Toyota wants it to be done.

He is correct on training the vehicle here is the last page of the TSB that explains what the technician is required to do before releasing the vehicle to the customer. View attachment 149686
 

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This doesnt make sense. I thought all 2020s had auto start stop by default. ??

So you should have had it when you bought it.
Yeah, its supposed to had it ON by default. But, mine was OFF by default all the time the week before returning to the dealer for the service appointment. I know, really odd, but that confirms that Toyota could do an update to keep the S/S off by default, because that’s what 95% of people want.
 

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Thanks. I swear I went through every post, but I missed it somehow. At this point, I'm going to just drive my Rav4 and enjoy it without going through all that BS. It drives well enough to not have to go in, argue with some service writer and have some tech mess with it for naught AND leave off my positive battery terminal cover yet again. If someone here on the board goes into their dealer and actually gets a second ECU TSB done and it works, I'll pursue it.
 

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There is software you can use to reset the ECU, but in my experience, disconnecting the battery and connecting the red and black leads together to drain any stored energy in the circuits is enough to clear everything. Then, after reconnecting the battery, you can start training the ECU to idle properly and shift smoothly at various driving conditions. The ones you want to focus are the ones the transmission struggles to shift smoothly. It took me a while to get this right. I tried multiple times(disconnect battery and retrain), but I got it and I was able to get my transmission to shift right after the dealership screwed up my transmission. That was on my 2017 gas RAV4 though.

Sent from my SM-A102U using Tapatalk
Why perform the TSB reprogramming then? I'd think that if they wanted to retrain the ECU, they'd just go through the pull the battery cables and retrain driving procedure, unless that's all the techs were doing for the TSB. Something was definitely changed after I had the dealer perform it and it's been that way ever since.
 

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My issue is more of a hard shift when coming to a full stop. Some people are having same issues as mine, but most are just experiencing the rolling hesitation lurk. With my car and others that posted, we have 2 problems with transmission. The hesitation stop doesn't bother me. I'm more concerned about the 2nd problem which is the hard downshift when coming to a full stop.
Toyota USA
I have the same exact problem with my 2019 Aventure. A loud grinding sound that sounds like a hard downshift. It happens mostly but not exclusively at 10 mph. Its not a consistant thing at all, and the RPM indicator doesn’t move significantly... if it was a downshift I would expect it to jump noticeably.. I’m at a loss, the dealer of course is giving me the “ we have never even heard of such a thing” ... The issue started exactly at 6500 miles. ‘Wheeeezzzrrr’ is the best way I can phonetically replicate it. I hope Toyota has answers soon, it’s starting to feel very lemon-like.
 

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. I’m at a loss, the dealer of course is giving me the “ we have never even heard of such a thing” ... The issue started exactly at 6500 miles. ‘Wheeeezzzrrr’ is the best way I can phonetically replicate it. I hope Toyota has answers soon, it’s starting to feel very lemon-like.

May want to try and record it for documentation purposes.
 

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Ha! I had logged into my Toyota Owners site and happened to check on the status of any recalls. I looked at the comments about the ECU reprogramming that the tech performed on my Rav4. According to him, the trans shifted correctly after he got done with it. Not even close bozo. In fact, I don't even think he performed the learning procedure. After reading how to do it from a poster here, there's really no way to perform it on our city streets in all practicality. You'd almost need to go to a barren empty road or unused runway, disconnect and reconnect the battery to clear the ECU, then hop in and perform the long driving procedure. There's no way to perform it on our city streets and not piss off some other driver in the process. What was Toyota thinking when they designed this thing, because I can't blame the tech (other than lying about the results of the "fix") for local road conditions where he can't practically perform the ECU training.
 

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Mine seems to be fine at the rolling stops still but it has transitioned into starting off in 1st gear more than 95% of the time now. It was the strangest thing. I normally only drive on surface streets since they are expanding the section of freeway that I would normally take for my commute. One evening I took the freeway and then I started getting the mooing sound, but only once. After that, I noticed that something was different. That difference was it no longer liek starting off in 2nd gear any more and it was back to how it was the day I bought it, but without the "clutch popping" rolling stops. It appears that it gets into 1st sooner and better than it was originally. I wonder if mine finally got the proper learning, however, I've taken it on the freeway after the update. Not sure if I like it or not since 1st gear is like a granny gear and it's not in it for very long.
 

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Mine's still staying in second during most rolling stops. First gear only on the count of 2 when almost stopped, below 1 kph usually. If I try to accelerate before it shifts down to first, then I get the dropped clutch lurch. If I am completely stopped, then it's no issue. I'd like to find a place to perform the training properly. On my city streets it's impossible to find a decent spot away from traffic. What Mode are you in most of the time? I'm in Sport around town.
 

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Mine's still staying in second during most rolling stops. First gear only on the count of 2 when almost stopped, below 1 kph usually. If I try to accelerate before it shifts down to first, then I get the dropped clutch lurch. If I am completely stopped, then it's no issue. I'd like to find a place to perform the training properly. On my city streets it's impossible to find a decent spot away from traffic. What Mode are you in most of the time? I'm in Sport around town.
How about a mall parking lot?

Sorry to say, but they should all be pretty much vacant now a days.
 
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