Transmission Clunk TSB L-SB-0042-25 (4 Viewers)

[cmfhsu]

I’m also experiencing the harsh downshifting when coming to a stop. Just called to make a 5k service appointment and was told that the tsb doesn’t apply to my 2025 gx. Am I just out of luck?

What TSB number did you reference when calling? You need to ask for L-SB-0042-25, not the earlier L-SB-0036-24, which is now closed and deprecated.

My July 2025 production GX got the updated calibration no problem, but it didn't fully solve the harsh downshift. I suggest lubricating the driveshaft slip yoke (especially) and u-joints - it makes a much bigger difference for harsh downshifting, and comes with the bonus of significantly smoother driving in general.

 

[Reef Surfer]

Thank you. I'm not 100% sure of the build date. I took ownership in August 2025, so probably a couple months prior to that. When I called service I offered several times to provide the TSB that you mentioned but they wouldn't take it. The guy entered my vin on his side and said that no TSB's came up.
I saw a couple people recommend greasing the driveshaft and will definitely give that a go.

 

[CCTX]

I haven't done the reflash yet but I agree that when I reset the TCM myself by disconnecting the battery's -ve, it works for maybe 500 miles or so and then it comes back and sometimes even worse.

The jolt coming to a stop is usually more prominent for the first few miles after I start driving. This morning, though, I happened to sit in the car while it was running for a few minutes before I started driving. I noticed no to minimal jolting even for the first few miles as usual. I plan to test this again by letting the car run for a few minutes before I start driving and see if it is indeed the case.

I understand the transmission oil takes a few minutes to get to the optimal operating temperature. But my question is the following: if the issue is just the algorithm, then would the temp still be a factor? if so, why?

Thanks in advance!

 

[RPMSTL]

My biggest issue that remains after the update is my first cold 1>2 shift in the morning is rough.
All other shifting is very decent now and this only happens on 1st shift of the day on completely cold
transmission .
Even if I let the truck sit for 6 hours the first shift is fine.

I have also noticed that if I let the car warm up for a while, the shifting is better.

 

[Roman]

My biggest issue that remains after the update is my first cold 1>2 shift in the morning is rough.
All other shifting is very decent now and this only happens on 1st shift of the day on completely cold
transmission .
Even if I let the truck sit for 6 hours the first shift is fine.

I have also noticed that if I let the car warm up for a while, the shifting is better.

This is exactly what I still experience after the update. Only the first cold shift after backing out of my driveway and it moves from 1st to 2nd. I have learned to live with it but wish it was addressed with the TCM update.

 

[4130]

I thought it was my imagination. Thanks for confirming the hard 1-2 shift after cold start after the transmission flash. I'm experiencing it, too. Not a big deal, but good to know it's "normal" behavior.

 

[CCTX]

This is exactly what I still experience after the update. Only the first cold shift after backing out of my driveway and it moves from 1st to 2nd. I have learned to live with it but wish it was addressed with the TCM update.

@Roman @4130 @RPMSTL
So not with slowing down to a stop but just the first 1st to 2nd shift? If so, did you have the jolt coming to a stop before the reflash? Thank you!!

 

[4130]

I had very mild downshift jolts. Post flash, all I notice is the 1-2 slight harshness on cold start. Everything else is smooth.

 

[cmfhsu]

This is exactly what I still experience after the update. Only the first cold shift after backing out of my driveway and it moves from 1st to 2nd. I have learned to live with it but wish it was addressed with the TCM update.

In my own experience, this has largely resolved itself after 1500 miles. It seems like this transmission takes a really long time to learn and adapt transmission hydraulic parameters. I still have a little bit of a harsh torque converter clutch engagement on light-medium throttle situations, but I suspect it's a similar case of simply needing to drive it for a long, long time to learn.

This behavior sounds a lot like what's described in GM's 8 speed class action documents, where the ATF hydraulic fluid bleeds out overnight from the piston that engages second gear's clutch. That causes a varying amount of clutch fill and apply time that is difficult to adapt to, since you have to purge all the air before the clutch will start to move, and you have no way of knowing how much air is in there. In GM's case, I believe the root cause of fluid bleeding overnight was manufacturing tolerances, so here's to hoping our transmissions don't have the same root cause.

 

[RPMSTL]

I did not have a jolt coming to a stop before or after the update.

 

[incognito.gx]

Truck is in for 10k so Im going to have them flash it and lube the U-joints/zerks etc to see if that helps. I’ve only had the “jolt” once or twice. By biggest issue is the lag on acceleration. I do agree the transmission could be smoother overall

 

[Roman]

@Roman @4130 @RPMSTL
So not with slowing down to a stop but just the first 1st to 2nd shift? If so, did you have the jolt coming to a stop before the reflash? Thank you!!

The jolt is minor but still happens from time to time...
What I notice sometimes is a jolt when accelerating and suddenly braking such as examples of sudden stops in traffic.

 

[cmfhsu]

The jolt is minor but still happens from time to time...
What I notice sometimes is a jolt when accelerating and suddenly braking such as examples of sudden stops in traffic.

I was able to totally eliminate this behavior by greasing my driveshaft zerks. Now when braking suddenly, whether via radar cruise or via manual braking, I don't have any noticeable jolt, at least once the transmission is warm.

Give it a try - it's a huge improvement.

 

[Roman]

I was able to totally eliminate this behavior by greasing my driveshaft zerks. Now when braking suddenly, whether via radar cruise or via manual braking, I don't have any noticeable jolt, at least once the transmission is warm.

Give it a try - it's a huge improvement.

Very interesting! I would have expected Lexus to take care of this when they so called resolved the issue with the update... What kind of grease did you use for the U-joints & Drive shaft?

 

[cmfhsu]

I used Lucas Red n Tacky grease for all driveline zerks, but the manual states any NLGI Grade 2 Lithium grease without Molybdenum is compatible. I promise it'll be the single most impactful thing you can do to make your GX drive like a luxury vehicle again.

There's a writeup on how to do it here in the forums somewhere I can't find right now, but the highlight is to be careful not to overfill the slip yoke - if you see the slip yoke starting to extend or move, stop immediately. It's possible to damage the slip yoke seal, transfer case, and differential by packing it full of non-compressible grease. I was able to get a good 15-20 pumps in without the slip yoke moving at all. The U-joints have a grease purge and cannot be damaged by overfilling.

My guess is that it's an annoying maintenance item that Lexus doesn't want to mandate, since you'll have to re-grease it every couple thousand miles, so they're trying to calibrate around it. I'm just thankful they still have zerk fittings, because greasable driveshafts tend to have much longer lifespans.

 

[cmfhsu]

Also, for anybody running aftermarket wheels without TPMS sensors, my transmission seems to behave differently after I installed & paired genuine Toyota TPMS sensors. Anybody who's having weird clunks & thumps and is just living with the constant TPMS light, it seems like shift logic and adaptation are possibly affected by the presence of accurate TPMS signals - though it's pretty hard to tell whether something else might have caused it.

Here's what I think has changed since I installed TPMS sensors:

• The transmission seems to launch from second gear much more frequently, avoiding the first gear downshift thump and reducing the delay between hitting the throttle and getting movement
• In bitter cold <30F, the torque converter clutch will start to lock up and go into "normal driving" logic much faster. Without TPMS sensors, it would stay in unlocked "warmup" mode for upwards of 5 minutes, whereas now it goes into normal lockup mode within 1-2 minutes
• It seems to have unlearned my harsh second gear TCC engagement within ~200 miles of driving - something that's been plaguing me for almost 2000 miles beforehand. Maybe the transmission will more readily go into learning / adaptation mode when the TPMS sensors are functioning, or maybe the TPMS light was preventing adaptation before.
  • I keep my factory wheels in the garage next to the GX, so it had valid TPMS signals every morning. Maybe the trans will adapt until the TPMS error is set?
  • I noticed you can access TPMS sensor temperatures from OBD2, so maybe tire temperatures are a part of transmission shifting & adaptation logic?
• The car seems to be much more wiling to downshift with the TCC locked when braking, bringing back the neck-swinging jerkiness as I'm slowing down. Bit of a downside, if I'm honest, but I understand that maximizing DFCO improves fuel economy.

 

[RCFGX]

Had this done when it came out still getting rough downshifts time to time.

 

[RPMSTL]

Finally got around to greasing the driveshafts. (5) zerk locations.

Did it improve the low speed shifting? - quite possibly.

Hard to say for sure with the placebo effect in play, but it does seem to shift smoother when in a stop and go situation - such as a momentary near pause when coming to a stop sign. Generally, I am getting back on the gas right as the vehicle is downshifting into 1st. What some call a rolling stop. Not a real stop, but close enough to pass.

I will keep monitoring it, but it seems better. No stiff shifts, so far.

I can't imagine the added grease at the u-joints did anything but greasing the yolk could definitely have an effect as they typically have a little wiggle room in the spline fitment since they are made to slip together without too much effort.

 

[ninjaboym5]

Thanks to this thread. Went to the dealer for the transmission software update. And luckily, my service adviser knows exactly what the update is unlike the other dealership I took my vehicle in for the 10k service. Much smoother on the downshift now. Didnt have the issue when I first acquired the vehicle. But seems to feel the downshift more and more in the last 3-4k miles. Hope this will last.

 

[cmfhsu]

Don't get your hopes too high before you give it 1-2000 miles. Myself and other forum members had great experiences just after it was flashed, but it's come back after a few thousand miles.