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1. Does downhill assist work (when the car downshifts a couple gears to increase engine braking) on cold start? Mine doesn't work until the engine is warm enough for the F gauges to activate, and I don't remember this being the case before.
2. Looking at the fluid change threads, I've seen it suggested that overfilling is better than underfilling to ensure the transmission performs normally. Is there any significant risk of damage if I overfill by, let's say around 1 quart? I want to avoid having to go through the temperature set procedure if possible.
I wouldn't imagine the downhill assist would work on cold start, as the entire idea behind engine braking is to use higher RPM's to decelerate the car, and high RPM's are mitigated when the engine is cold. Also, having higher fluid levels is better than lower fluid levels, as these transmissions will go positively bonkers if their level is even lower than normal. It is still best to be within the specifications though, probably more than 3/4ths for a quart over might be a bit too much. Don't know for sure though.
1. Does downhill assist work (when the car downshifts a couple gears to increase engine braking) on cold start? Mine doesn't work until the engine is warm enough for the F gauges to activate, and I don't remember this being the case before.
2. Looking at the fluid change threads, I've seen it suggested that overfilling is better than underfilling to ensure the transmission performs normally. Is there any significant risk of damage if I overfill by, let's say around 1 quart? I want to avoid having to go through the temperature set procedure if possible.
Any help is appreciated.
1. The transmission is in limp mode/detuned when the engine is cold. That is why the downshifts don't have throttle blips (using paddles or in auto mode) and very limited engine braking available. It is to protect the transmission when it is cold and to ensure longevity. The transmission will also auto upshift in manual mode at around 4500 rpm, if the engine is cold. Again, to ensure the transmission and engine are properly warmed up before pushing it hard.
2. No don't overfill. It could cause some foaming issues and potentially can damage the engine.
1. The transmission is in limp mode/detuned when the engine is cold. That is why the downshifts don't have throttle blips (using paddles or in auto mode) and very limited engine braking available. It is to protect the transmission when it is cold and to ensure longevity. The transmission will also auto upshift in manual mode at around 4500 rpm, if the engine is cold. Again, to ensure the transmission and engine are properly warmed up before pushing it hard.
That makes sense, but I recall seeing it downshift from 8th to like 5th even when cold on the steep hill near my place. Even in 5th it only ends up at roughly 2500 RPM. Would detuned mode prevent all auto downshifts or just aggressive ones, like the ones the car gives you when braking into corners in sport mode?
Thank you everyone for answering - I'll look into just resetting the level.
That makes sense, but I recall seeing it downshift from 8th to like 5th even when cold on the steep hill near my place. Even in 5th it only ends up at roughly 2500 RPM. Would detuned mode prevent all auto downshifts or just aggressive ones, like the ones the car gives you when braking into corners in sport mode?
Thank you everyone for answering - I'll look into just resetting the level.
The transmission has artificial intelligence built into it so it takes a lot of inputs such as, load, temperatures, driving habits etc. into account. When the engine is cold, the rev limiter starts at only 4500 rpm so if the downshift engine speed exceeds 4500 rpm then it will refuse the downshift both in auto and manual mode. If it is a slower speed, descending downshift where the lower gear is within the maximum engine speed then it will allow it. The rev limiter works slowly all the way to around 7400 rpm (redline 7300 rpm) once it is fully warmed up.
If that's the case, hill assist should work, right? By the time I need the engine braking the redline has usually moved up to 5500-6000 rpm. It will downshift if I pull the paddles in D for engine braking, but I'm wondering if it works automatically in everyone else's cars. I recently added 3/4 of a quart of fluid because I was having issues and while it definitely shifts faster and feels less sloppy now, the timing of the shifts are still awkward. I was thinking maybe it's still low on fluid and the lack of hill assist is another symptom.
I have always understood that overfilling a transmission will do more damage than underfilling. Blowing seals, foaming, overheating all can happen with overfilling. If you have an issue, overfilling it won’t help fix the issue, it may help cover it up temporarily. Also, I have a very hard time believing Toyota/Lexus accept the idea that these trans run better overfilled. Hey, maybe your right, but I would be surprised if that was the case. I think they have their **** together over there.😂
I would follow the process of topping off the transmission to spec than add no more than 1/4 qt more. Most standards allow for 1/2qt overfill margin for human error but not all. If you have not pulled the battery to reset the transmission learning I would do that also. I have learned to do that every 5-6k because my torque converter gets really noticeable locking up at 2k and after a reset it feels less noticeable. I think it’s the transmission trying to combat me beating up the trans by giving a larger fuel dip to protect internals in the trans.
I have always understood that overfilling a transmission will do more damage than underfilling. Blowing seals, foaming, overheating all can happen with overfilling. If you have an issue, overfilling it won’t help fix the issue, it may help cover it up temporarily. Also, I have a very hard time believing Toyota/Lexus accept the idea that these trans run better overfilled. Hey, maybe your right, but I would be surprised if that was the case. I think they have their **** together over there.😂
I would follow the process of topping off the transmission to spec than add no more than 1/4 qt more. Most standards allow for 1/2qt overfill margin for human error but not all. If you have not pulled the battery to reset the transmission learning I would do that also. I have learned to do that every 5-6k because my torque converter gets really noticeable locking up at 2k and after a reset it feels less noticeable. I think it’s the transmission trying to combat me beating up the trans by giving a larger fuel dip to protect internals in the trans.
It is always best to fill to the manufacturer's specifics. There is some margin for error but you should always do the temperature level set. From what I've seen though, the lower the level the worse these transmissions cope with it. Overfilling or underfilling is pretty much not a good idea anyhow, it's best to be right where the transmission was mean't to be.
I believe this procedure was for the IS F but since it's basically the same transmission, it should work just fine. Temperature checking may be a pain but it is probably worth it. And yes, it is a good idea to disconnect the battery for a while, plug it back in then go for a bit of a spirited drive. As others have said it resets the learning.
It is always best to fill to the manufacturer's specifics. There is some margin for error but you should always do the temperature level set. From what I've seen though, the lower the level the worse these transmissions cope with it. Overfilling or underfilling is pretty much not a good idea anyhow, it's best to be right where the transmission was mean't to be.
I believe this procedure was for the IS F but since it's basically the same transmission, it should work just fine. Temperature checking may be a pain but it is probably worth it. And yes, it is a good idea to disconnect the battery for a while, plug it back in then go for a bit of a spirited drive. As others have said it resets the learning.
Good info! Do we know if TechStream gives us the temp of the transfluid? I ask this because this process is very similar to our Mercedes however, the software that is used (STAR/DAS/Xentry) shows you the operating temp of the transfluid so you can precisely open the drain to bleed off the excess once the trans is up to proper temp. The whole off/on/blinking icon seems like a very large range of temp.
Good info! Do we know if TechStream gives us the temp of the transfluid? I ask this because this process is very similar to our Mercedes however, the software that is used (STAR/DAS/Xentry) shows you the operating temp of the transfluid so you can precisely open the drain to bleed off the excess once the trans is up to proper temp. The whole off/on/blinking icon seems like a very large range of temp.
-Nigel
Yes, there is a TechStream version of this procedure where you monitor the trans fluid temps. You basically want the temp to be between 113 to 133°F (45 to 56°C). That range is when the icon is ON using the procedure listed above. The icon is OFF below 113°F and is blinking when temp is above 133°F.
Yes, there is a TechStream version of this procedure where you monitor the trans fluid temps. You basically want the temp to be between 113 to 133°F (45 to 56°C). That range is when the icon is ON using the procedure listed above. The icon is OFF below 113°F and is blinking when temp is above 133°F.
Excellent!! Saved for future use when the time comes!
Appreciate. I wish we had a stickied thread with stuff like this in it! I wonder if we can get one to put how -to's and procedures. Every other forum I am on we have a stickied thread that is like 10+ pages of common and uncommon stuff to do on the car. It's a real life saver. The Toyota forum on ToyotaNation is insane. Down to the part of different fluids/filters that can be used on a particular model/sub thread.
Excellent!! Saved for future use when the time comes!
Appreciate. I wish we had a stickied thread with stuff like this in it! I wonder if we can get one to put how -to's and procedures. Every other forum I am on we have a stickied thread that is like 10+ pages of common and uncommon stuff to do on the car. It's a real life saver. The Toyota forum on ToyotaNation is insane. Down to the part of different fluids/filters that can be used on a particular model/sub thread.
It would make our life easier. IE: Stickied - DIY thread. Then people can could start posting/linking to oil changes, trans fluid change (normal/TVD), interior ambient lighting retrofits/mods, headlight adjustment, spoiler swaps, interior part removals (console, pillars, seats..etc.). I get excited just thinking of all this knowledge that could be sitting there for people to enjoy and add.
I would LOVE to be able to do a power folding mirror retro fit... that is IDEAL! I'm still hoping Barry can help me out with part numbers for the face lifted version and I have no problem taking the plunge and being the test guy for it.
09-30-21, 06:03 PM
a few questions about the transmission
