LX570 Lean/Sag (1 Viewer)

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It’s probably worthwhile to consider if a lean is caused by the AHC system, or if it’s just a tendency due a weaker spring in the suspension.

I would attribute it to the latter. This is not a new thing to trucks/SUVs. It's been common since the beginning of these types of vehicles. AHC or KDSS not withstanding. Plenty of "misconstrued KDSS", or just plain 200-series lean issues on these boards.

Fuel weight is probably worth considering. The tank is offset and on the passenger side. Weight can swing almost 150lbs to/from that side depending on fuel level.

4x4’s leaning overtime is common. When there is tall and soft springs involved, most SUVs will take a set one way or another. Take a look at any SUV/truck forum and this will be a very relevant topic. Overtime, the lower/weaker spring side will further droop as more weight is transferred to the lower side springs. Something < ¾” isn’t really a concern.

During the days of torsion bars, it was easy to re-level the ride with a few cranks. 100-series with AHC experienced these issues as well. In those vehicles, torsion bar front suspensions could be adjusted to compensate to a degree. Larger leans needed the rear weaker spring supported.

Trim packers have been around for as long as 4x4s to address this very thing. Adding 5/10/15/20mm trim packers to the lower side rear spring is the real solution.

IIRC, the AHC system has 3 height sensors. 1 at each front wheel. One for the rear axle. The system has some but limited ability to compensate for height mistmatch side to side. If the system is like the 100-series, most of the lean is propagated by a weak spring at the rear position. Systems compensation or adjustment at the front will only go so far.

I don't believe that this is an AHC ECU issue. From a control loop and diagnostic POV, it doesn't make sense. It's probable that the newer AHC ECUs have revised/updated control logic to compensate for lean, rather than the original ECU having a fault. Sure, there's one example of it solved with that, but IMO, I believe it's more likely that they re-calibrated the heights upon installation of the ECU.

Coming full circle, focusing on the AHC system is a red herring. It may be able to compensate. But the actual root cause is a weaker spring, particularly at the rear axle. Trim packers are the solution here as they always have been. It's a rather easy 30 minute operation to install at the lower side.
 
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CLHickman said:
You could find some on eBay used. What's the issue with yours? Most issues are programming and not an actual malfunction with the ECU.
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The Left rear corner is 1" lower than the right at every height. I tried fiddling with the height sensor on that wheel to see if I could adjust it that way. If I adjusted the LR sensor to attempt to raise that wheel, nothing happened. If I adjusted the LR sensor to lower by 1", the RR side adjusted on its own by exactly the same amount. Could be a calibration issue. I'm going to order the Techstream cable and attempt to troubleshoot that way. If that doesn't work I'll take it down to Lexus for some diagnostics before I go replacing anything.
 
TeCKis300 said:
It’s probably worthwhile to consider if a lean is caused by the AHC system, or if it’s just a tendency due a weaker spring in the suspension.

I would attribute it to the latter. This is not a new thing to trucks/SUVs. It's been common since the beginning of these types of vehicles. AHC or KDSS not withstanding. Plenty of "misconstrued KDSS", or just plain 200-series lean issues on these boards.

Fuel weight is probably worth considering. The tank is offset and on the passenger side. Weight can swing almost 150lbs to/from that side depending on fuel level.

4x4’s leaning overtime is common. When there is tall and soft springs involved, most SUVs will take a set one way or another. Take a look at any SUV/truck forum and this will be a very relevant topic. Overtime, the lower/weaker spring side will further droop as more weight is transferred to the lower side springs. Something < ¾” isn’t really a concern.

During the days of torsion bars, it was easy to re-level the ride with a few cranks. 100-series with AHC experienced these issues as well. In those vehicles, torsion bar front suspensions could be adjusted to compensate to a degree. Larger leans needed the rear weaker spring supported.

Trim packers have been around for as long as 4x4s to address this very thing. Adding 5/10/15/20mm trim packers to the lower side rear spring is the real solution.

IIRC, the AHC system has 3 height sensors. 1 at each front wheel. One for the rear axle. The system has some but limited ability to compensate for height mistmatch side to side. If the system is like the 100-series, most of the lean is propagated by a weak spring at the rear position. Systems compensation or adjustment at the front will only go so far.

I don't believe that this is an AHC ECU issue. From a control loop and diagnostic POV, it doesn't make sense. It's probable that the newer AHC ECUs have revised/updated control logic to compensate for lean, rather than the original ECU having a fault. Sure, there's one example of it solved with that, but IMO, I believe it's more likely that they re-calibrated the heights upon installation of the ECU.

Coming full circle, focusing on the AHC system is a red herring. It may be able to compensate. But the actual root cause is a weaker spring, particularly at the rear axle. Trim packers are the solution here as they always have been. It's a rather easy 30 minute operation to install at the lower side.
Click to expand...
@TeCKis300 thanks for putting some thought into this. I think the key clue here is that the height difference in that corner is consistent regardless of the circumstance--H/N/L, loaded, or unloaded. That rules out fuel or any other weight induced sag which the system is already compensating for.

I'm not sure about the LX470, but the LX 570 has four height sensors--one at each wheel. This being the case, I'm not sure what impact a weak spring would have on the system. The accumulators are independent and should have the ability to control pressures in each corner to level the vehicle. If it had a weak spring I wonder if it would just increase hydraulic pressure at that corner to compensate?

The manual points to three potential areas of concern when Height control function is normal, but vehicle height is uneven--Initialization, Height control sensor link, or Suspension control ECU. The 1,824 page section on the AHC is a mind-bender (especially when the hotlinks to relevant sections in my copy don't work).
 
^Good stuff.

Even with 4 sensors, I'm not sure the system has the ability to independently control height at each corner. With the way it lifts through L/M/H alternating between an axle at a time, I suspect the system can only control AHC pressure independently per axle, rather than per corner.
 
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TLCLVR said:
The Left rear corner is 1" lower than the right at every height. I tried fiddling with the height sensor on that wheel to see if I could adjust it that way. If I adjusted the LR sensor to attempt to raise that wheel, nothing happened. If I adjusted the LR sensor to lower by 1", the RR side adjusted on its own by exactly the same amount. Could be a calibration issue. I'm going to order the Techstream cable and attempt to troubleshoot that way. If that doesn't work I'll take it down to Lexus for some diagnostics before I go replacing anything.
Click to expand...
Hello, I'm having the same issue come up with LX. Did you figure out what was the cause and replacement part to fix the rear sag? Thanks
 
Roc14 said:
Hello, I'm having the same issue come up with LX. Did you figure out what was the cause and replacement part to fix the rear sag? Thanks
Click to expand...
There really needs to be a 200 series “lean” wiki.

I think there is a lot of good info in this post
Post in thread 'LX570 Lean/Sag'
LX570 Lean/Sag - https://forum.ih8mud.com/threads/lx570-lean-sag.918190/post-12752944

weve learned a bit about 200 series AHC since then, but I think it mostly holds true.

I don’t think it’s worth chasing lean, unless it’s way off, but if I were, I would attack it in these steps. I’ll preface this with a statement that this isn’t fact by any means, but more an educated guess.

1a. Get techstream and connect to tha AHC module. Verify height sensors aren’t in any crazy state.
1. Park truck on flat spot.
2. use techstream AHC module and open both gate valves a couple times with the test utility. This will balance the left and right side of each axles system pressure.
3. Remeasure corner heights. this should let you know if your lean is sensor related or spring related. Possibly could be an ECU issue as well, but doesn’t seem likely.

If you are level at this point, then you should be able to move sensors to get the system pressures after an L to N adjustment to be closer to balanced and the truck should ride level more often, as well as probably make less adjustments on the fly.

If you are not level, then the only real way to get level is with spring adjustments (either spacers or new springs). You could also opt to adjust sensors so that the L to N adjustment gets you similar to the post gate valve measurement Then you would at least lessen the on the fly adjustments.

Honestly I have no idea how precise you can be with making physical sensor adjustments. But if you got with a .5 inches, I’d probably call that good.
 
lx200inAR said:
There really needs to be a 200 series “lean” wiki.

I think there is a lot of good info in this post
Post in thread 'LX570 Lean/Sag'
LX570 Lean/Sag - https://forum.ih8mud.com/threads/lx570-lean-sag.918190/post-12752944

weve learned a bit about 200 series AHC since then, but I think it mostly holds true.

I don’t think it’s worth chasing lean, unless it’s way off, but if I were, I would attack it in these steps. I’ll preface this with a statement that this isn’t fact by any means, but more an educated guess.

1a. Get techstream and connect to tha AHC module. Verify height sensors aren’t in any crazy state.
1. Park truck on flat spot.
2. use techstream AHC module and open both gate valves a couple times with the test utility. This will balance the left and right side of each axles system pressure.
3. Remeasure corner heights. this should let you know if your lean is sensor related or spring related. Possibly could be an ECU issue as well, but doesn’t seem likely.

If you are level at this point, then you should be able to move sensors to get the system pressures after an L to N adjustment to be closer to balanced and the truck should ride level more often, as well as probably make less adjustments on the fly.

If you are not level, then the only real way to get level is with spring adjustments (either spacers or new springs). You could also opt to adjust sensors so that the L to N adjustment gets you similar to the post gate valve measurement Then you would at least lessen the on the fly adjustments.

Honestly I have no idea how precise you can be with making physical sensor adjustments. But if you got with a .5 inches, I’d probably call that good.
Click to expand...
Thanks for the reply. I pulled the truck into the garage and measured the 4 corners. There was no lean, it went away, but when I pulled out of the garage it was 1 inch on the driver side rear. The driveway has a slight pitch. Weird going to keep an eye on it. It's a 2011 185k miles had it for 10 years. Going to change the globes and flush AHC fluid. Updating front shocks this week as well. Thanks again, o e more question. Where do you suggest picking up techstream?
 
My driver (left) rear fender is sitting 1.6"+/-0.1" lower than the right at L, N, and H. Having read through a ton of AHC threads over different timelines, is swapping the LR spring for a RR spring still the consensus way to go? I saw TeCKis suggest spring packers at some point. Any pros/cons to either approach?
Thanks

P.S. From what I have read, changing the accumulators and/or flushing seems to help restore ride quality but any correction to the DR height seems to be short-lived once the AHC adjusts.
 
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Add to this thread, but I have limited knowledge, so take it for what it’s worth.

I just got my LX back from the shop with the Wescott kit installed and a right rear spring replacing the left rear.

I still have about the same amount of lean. I do not have Techstream and so I haven’t looked at the HOU to see what the offset is between left and right rear, I think that’s my next Step, but I thought the spring would simply correct the lean. 🤷‍♂️
 
eXpLoreLX said:
Add to this thread, but I have limited knowledge, so take it for what it’s worth.

I just got my LX back from the shop with the Wescott kit installed and a right rear spring replacing the left rear.

I still have about the same amount of lean. I do not have Techstream and so I haven’t looked at the HOU to see what the offset is between left and right rear, I think that’s my next Step, but I thought the spring would simply correct the lean. 🤷‍♂️
Click to expand...
I’ll start this by saying, unless you have a crazy unsafe lean, it’s not worth chasing it. (Anything less than an inch)

Have to remember there are 2 states your suspension can be in when on a level surface. A state that is set when the truck adjusts to a predetermined height based on the height sensors. Then a 2nd state where the gate valves that balance pressure between left and right have been opened. These two states are certainly not necessarily equal. Unless you know which state you are measuring, you are just throwing crap into a fan. If you are always measuring the state right after a height adjustment, it doesn’t matter what you do to the suspension it’s going to rest at what the AHC ECU sets it at based on the height sensors.

(Speculation from here on)
In a perfect world I would think you’d want to do the typical 4x4 leveling with shims or fresh springs, but only after using Techstream to open the gate valves and make sure the pressure between left and right is even before shimming. Then either use HOU or manually adjusting sensors to get the AHC ECU height adjustment to move to level. I think this would lead to less on the fly adjustments that bother some people and get a more consistent leveling between left and right for you OCD types.
 
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lx200inAR said:
I’ll start this by saying, unless you have a crazy unsafe lean, it’s not worth chasing it. (Anything less than an inch)

Have to remember there are 2 states your suspension can be in when on a level surface. A state that is set when the truck adjusts to a predetermined height based on the height sensors. Then a 2nd state where the gate valves that balance pressure between left and right have been opened. These two states are certainly not necessarily equal. Unless you know which state you are measuring, you are just throwing crap into a fan. If you are always measuring the state right after a height adjustment, it doesn’t matter what you do to the suspension it’s going to rest at what the AHC ECU sets it at based on the height sensors.

(Speculation from here on:)
In a perfect world I would think you’d want to do the typical 4x4 leveling with shims or fresh springs, but only after using Techstream to open the gate valves and make sure the pressure between left and right is even before shimming. Then either use HOU or manually adjusting sensors to get the AHC ECU height adjustment to move to level. I think this would lead to less on the fly adjustments that bother some people and get a more consistent leveling between left and right for you OCD types.
Click to expand...

Well I just measured again to be sure, but it's about 1 3/16 or so... and I don't care if it's perfect, but I had that just about the exact same height difference previously prior to the brand new passenger coil (right side coil) being installed on the driver side (left side). Sounds like I should consider some other items to investigate. The right rear sits at about 40" the driver side is 38 13/16" (measured in High). So it's close and from the back it's barely noticeable, but when you see it from the side it and walk around to the other side it's quite obvious that the passenger side is taller.

Perhaps the gate valve is the solution? Otherwise I might just lower the right side slightly with the sensor.
 
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eXpLoreLX said:
Well I just measured again to be sure, but it's about 1 3/16 or so... and I don't care if it's perfect, but I had that just about the exact same height difference previously prior to the brand new passenger coil (right side coil) being installed on the driver side (left side). Sounds like I should consider some other items to investigate. The right rear sits at about 40" the driver side is 38 13/16" (measured in High). So it's close and from the back it's barely noticeable, but when you see it from the side it and walk around to the other side it's quite obvious that the passenger side is taller.

Perhaps the gate valve is the solution? Otherwise I might just lower the right side slightly with the sensor.
Click to expand...
So, if you are measuring in high, then i assume you are parking on your flat surface and then moving it into high with no driving after that. With that assumption, I would expect you are measuring the height that the AHC ECU is setting based on the sensors. I would not expect your truck to ever settle at a different height no matter what you did to the suspension in that scenario, because the height will strictly be set by whatever pressure is needed at each corner to get the height sensors where the ECU wants them.

I probably should have been more clear above. When the truck sets the height during a lift/drop, that height is set by the sensors. Once the gate valves open (which they do periodically) then the truck will have balanced pressure between left and right (not necessarily balanced height). Now you are in the position of any standard 4x4 and at the mercy of how balanced your load and springs are directly affecting if the truck is sitting level. The mystery is, how often does the truck balance left and right with the gate valves, and then how often does it correct the height based on the sensors after it does the balance. I think there is a good chance that every time you stop at a red light with foot on brake for more than 4-5 seconds it adjusts back to sensor height.

All that said, if you are 1.375" off from one side to the other right after a height change, I would suspect your only way to get that closer is to move one of your sensors to get them closer to matching. HOU can only offset a sensor +- 0.8", so technically if they were currently at 0 you could use HOU to get it corrected by offsetting one up and the other down, but i bet that's more trouble than just adjusting a sensor.

But keep in mind, the AHC ECU is adjusting height frequently, so what you see when you are parked may have little to do with what happens while you are actually on the road.
 
I’m not sure whether the following explains the persistent drive side lean/sag we see (I’m not an engineer):

Though, it may be the crown of the road forcing the suspension system to equalize left to right with a slight dip on the driver’s side.

I’ve noticed that when I bump into high mode and then back into neutral, I generally dont have lean/sag….the sensors work to get everything even…however, after driving a while, it does seem common to end up with the passenger side slightly higher than driver.

Roads are generally slanted so the driver sits higher than the passenger so rain will drain off…

What if the vehicles, sensing the lean of the vehicle caused by the road, is fixing the vehicle so the occupant doesn’t feel the lean caused by the road…which then causes the vehicle to “settle” in a driver down passenger up orientation over time.

One way to test this is to bump the vehicle into high then neutral…and let it sit idling on a flat surface for 20-30 minutes and see whether a sag/lean occurs…

Then take the vehicle, bump it into high then neutral and let us sit idling on a crowned road for 20-30 minutes to see whether a lean occurs.

You could even park it on the wrong side of a crowned road to see if the sag shifts to the other side.
 
highfructose said:
I’m not sure whether the following explains the persistent drive side lean/sag we see (I’m not an engineer):

Though, it may be the crown of the road forcing the suspension system to equalize left to right with a slight dip on the driver’s side.

I’ve noticed that when I bump into high mode and then back into neutral, I generally dont have lean/sag….the sensors work to get everything even…however, after driving a while, it does seem common to end up with the passenger side slightly higher than driver.

Roads are generally slanted so the driver sits higher than the passenger so rain will drain off…

What if the vehicles, sensing the lean of the vehicle caused by the road, is fixing the vehicle so the occupant doesn’t feel the lean caused by the road…which then causes the vehicle to “settle” in a driver down passenger up orientation over time.

One way to test this is to bump the vehicle into high then neutral…and let it sit idling on a flat surface for 20-30 minutes and see whether a sag/lean occurs…

Then take the vehicle, bump it into high then neutral and let us sit idling on a crowned road for 20-30 minutes to see whether a lean occurs.

You could even park it on the wrong side of a crowned road to see if the sag shifts to the other side.
Click to expand...

I like the theory. I definitely agree there is a chance that if you stop at a red light and the truck adjusts height to level itself, and then you stop and park shortly their after, the truck will be setting based on however it adjusted height when on the road. Just another reason in the long list of reason to not bother "chasing lean" on an LX unless it actually seems to be causing something unsafe to be happening.

I don't think you have to let anything sit for 20-30min. If you are in "D" and are stopped with foot on brake, Truck will almost always adjust height after 5-6seconds, if the ECU thinks its necessary.
 
lx200inAR said:
I like the theory. I definitely agree there is a chance that if you stop at a red light and the truck adjusts height to level itself, and then you stop and park shortly their after, the truck will be setting based on however it adjusted height when on the road. Just another reason in the long list of reason to not bother "chasing lean" on an LX unless it actually seems to be causing something unsafe to be happening.

I don't think you have to let anything sit for 20-30min. If you are in "D" and are stopped with foot on brake, Truck will almost always adjust height after 5-6seconds, if the ECU thinks its necessary.
Click to expand...
I decided to confirm further, as you were correct previously that I was in my garage on a nice flat surface and shifted into High to measure. So I went for a coffee run (Starbucks of course so I can see my Adv motorcycle buddies) and then remeasured when I got home (in N)

The difference is still essentially the same; about 1.20". I might just try adjusting the senor slightly but other than than not going to "chase lean" as mentioned it may be a fools errand!
 
eXpLoreLX said:
I decided to confirm further, as you were correct previously that I was in my garage on a nice flat surface and shifted into High to measure. So I went for a coffee run (Starbucks of course so I can see my Adv motorcycle buddies) and then remeasured when I got home (in N)

The difference is still essentially the same; about 1.20". I might just try adjusting the senor slightly but other than than not going to "chase lean" as mentioned it may be a fools errand!
Click to expand...
In the DIY Smartphone APP thread, I posted a OBD Fusion Dashboard that monitors all the important AHC functions. If you are really into it, you can install that, and then watch how much things move around as you drive around. The only thing that sucks is that the refresh rate isn't great, so you may not see everything, or may see things on a delay. But it is useful to get a better idea of whats going with the suspension. I never do any bleeding or fluid swapping without having that running. As there is generally a lot more going on than what the dashboard shows you.

forum.ih8mud.com

DIY Smartphone Scan Gauge - OBD Fusion

I did this and couldn’t locate one. I checked all sections under the Toyota advanced pack. If you bought the Toyota PID pack for $10 it should be there. This is where mine is. You may need to rescan all of the PIDs while in Park if it’s not showing up… it’s possible it’s hidden as OBD Fusion...
forum.ih8mud.com forum.ih8mud.com
 
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