Solution to intermittent AHC lean? (1 Viewer)

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I did the searches and didn’t find a solution that was settled.
Some replace a very expensive part and hope…I don’t like that idea.

I had enough lean the passenger side that I decided to do a moderate ahc lift on driver side side and mild ahc lift on driver side to even it out with about a 0.5” lift total over where the passenger side was.

So I adjusted all my ahc sensors and straightened everything out…

then when I go into low mode and put it back into neutral, it cranks the passenger side up quite a bit higher than the driver again.

If I put it in high mode and then go back down to neutral, everything appears even again.

So the system gets goofy going from low to neutral…

Does this really require the replacement of a part? Has anyone else had this specific problem, identified the cause, and implemented a specific solution?
 
My LX almost always leans to one side slightly... I thought it was normal.
Mine was significant. The passenger side looked like it was almost in high mode…driver side looked almost in low.

After the ahc lift I started readjusting at one point because I again had a side markedly higher than the other…then I realized if I cycled through high and back down to normal it fixed everything.

I think the issue has been there for a long time because when my truck is “level” left to right, the truck pulls to the right moderately…indicating that when I got my alignment done after my tires, the truck was in a “leaned” position.

Also, when I first got the car it pulled hard to the right…I assumed it was a tire issue so I got them replaced and alignment done. In reality, the car probably had this significant lean that I didn’t notice yet was causing the truck to pull to the side…and I got it aligned while in leaned mode and just didn’t notice it until I took a look at the passenger side with a critical eye one day…

stupid me I always approach the car from the driver side and always parked it in low mode so I never really noticed how far out of whack the passenger side was in normal until I one day decided to always leave it in normal height mode…then I started noticing the passenger side when I happened to approach from the passenger side.
 
Like the KDSS lean, AHC lean is a fallacy. Not that it doesn't lean, but it's not because of AHC or KDSS.

AHC as part of its operation, will equalize pressures left to right. So while it may appear to be able to level side to side, it will equalize at speed, or in transitions as you're finding.

Root cause, as for any slinky 4x4, is wear and settling of the coil springs. As cars age, a weaker side will show. With continual lean, more and more weight gets put on said coil, further causing the weaker coils to settle more than others.

Appropriate fix, like for KDSS, is to use coil shim packers. Readily available in 5/10/20/30mm sizes. We can't readily shim or trim the front spring. So a 5 or 10mm added to the rear spring in the low corner is the fix. Or new fresh springs, but nothing wrong with trim packers.
 
Like the KDSS lean, AHC lean is a fallacy. Not that it doesn't lean, but it's not because of AHC or KDSS.

AHC as part of its operation, will equalize pressures left to right. So while it may appear to be able to level side to side, it will equalize at speed, or in transitions as you're finding.

Root cause, as for any slinky 4x4, is wear and settling of the coil springs. As cars age, a weaker side will show. With continual lean, more and more weight gets put on said coil, further causing the weaker coils to settle more than others.

Appropriate fix, like for KDSS, is to use coil shim packers. Readily available in 5/10/20/30mm sizes. We can't readily shim or trim the front spring. So a 5 or 10mm added to the rear spring in the low corner is the fix. Or new fresh springs, but nothing wrong with trim packers.
Interesting. Odd that Lexus didn’t design the system to level the car…and instead designed it to equalize the pressure.

I’ll have to try replacing the springs on the driver side.

It looks like the part numbers for the job follow:

4823160D21 Lexus Is the rear spring

$135



4813160D91 Lexus is the front spring

$135
 
I’ve installed a lev-o-gage that gives me an easy indicator of when my vehicle is “off kilter.”

I’ve noticed that when I have lean, it’ll rest at about a 5 degree tilt, generally leaning to make the driver side low.

However sometimes it’s the driver side which is high.

If I quickly choose high mode…and let it lift a little…I can bump it back down to normal height and it will equalize the height left to right.

At this point I kind of want to remove lots of strain from the ahc system…preferably via uprated springs.

I notice that under normal cornering, the body rolls up to 15 degrees before settling. I think Lexus tried to make this vehicle as soft and supple as it could be…and I don’t need that.

Has anyone come across an uprated coil for the front?

51EFE2CE-C62B-49C8-BD96-8BDA9E98FD5A.jpeg
 
What's the measurement difference when parked? Are we talking about ~.5 to 1" or more? Some lean is always expected and within normal.

I guess other than the static lean, I'm confused as to what you're trying to solve.

Taking "strain" off AHC may just mess up the system as the system is designed for what it's handling, and from my experience can handle some serious weights. It's already has stiffer secondary main springs on the front axle to handle cornering loads. Monitoring the AHC system via OBD-II that reports heights for each wheel, when turning, the loaded corner barely compresses. The system is hyper active to engage the secondary springs and use compression damping to support flat cornering. Of course, there will still be lean as tires sidewalls flex and body mounts flex as this is a tall body on frame vehicle.
 
What's the measurement difference when parked? Are we talking about ~.5 to 1" or more? Some lean is always expected and within normal.

I guess other than the static lean, I'm confused as to what you're trying to solve.

Taking "strain" off AHC may just mess up the system as the system is designed for what it's handling, and from my experience can handle some serious weights. It's already has stiffer secondary main springs on the front axle to handle cornering loads. Monitoring the AHC system via OBD-II that reports heights for each wheel, when turning, the loaded corner barely compresses. The system is hyper active to engage the secondary springs and use compression damping to support flat cornering. Of course, there will still be lean as tires sidewalls flex and body mounts flex as this is a tall body on frame vehicle.
Bottom of driver side fender is 34.5 vs 36.25 on passenger after a drive.

They are 35.5 vs 35.75 after cycling up to high and then back to normal


Turn left in parking lot (compressing driver side spring) results in 5 degree tilt

Turn right in parking lot (compressing driver/low side spring) results in 10-15 tilt

Following a couple turns, vehicle is resting at a 2.5 degree tilt with driver side low again.

Bumping up to high momentarily and then back to normal equalizes height again.
 
Bottom of driver side fender is 34.5 vs 36.25 on passenger after a drive.

They are 35.5 vs 35.75 after cycling up to high and then back to normal


Turn left in parking lot (compressing driver side spring) results in 5 degree tilt

Turn right in parking lot (compressing driver/low side spring) results in 10-15 tilt

Following a couple turns, vehicle is resting at a 2.5 degree tilt with driver side low again.

Bumping up to high momentarily and then back to normal equalizes height again.
25 degree tilt on driver side spring during 15 mph turn to right

15 degree tilt with 15 mph turn to left.

Starting to think you’re right a d the springs on the driver side need to be replaced.
 
25 degree tilt on driver side spring during 15 mph turn to right

15 degree tilt with 15 mph turn to left.

Starting to think you’re right a d the springs on the driver side need to be replaced.
Well...something else to consider, at those speeds, it's possible one of your turns had the secondary spring engaged and one didn't.
 
Well...something else to consider, at those speeds, it's possible one of your turns had the secondary spring engaged and one didn't.
That’s something to consider.

I’m going to keep testing at various speeds.

within a parking lot at 5mph, the lean appears to be 5 degrees on “the strong side” and 10-15 on the weak.
 
The coils from the 2021 lx570 are in. The following are measurements I took. Take the spring compression info with a grain of salt. It’s really awkward balancing plates on top of the springs and then attempting to measure from the same spot to the same spot. If anyone has pointers on being more repeatable/scientific, let me know.

-2021 front springs is 17.75” tall & 5 1/16th across (15mm thick compared to 16mm for my 2011 front coils)
16.5” with 88 lbs on it

-Left rear (same across all lx570’s) is 16.25” (14mm thick) & 7” across
16” with 113 lbs (awkward probably not accurate)

-Right rear (same across all lx570’s) is 20” & 7” across (13mm thick). I was unable to balance plates and kettlebells on it…too tippy.
 
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I replaced the left rear coil with a right rear coil (which is like 3” taller and obviously stronger) in order to give the car a more equal distribution of its weight handling…and now the front left coil, which was always the saggy/lowered spot on the car, is 2-3” taller than the front right…which to me indicates that if I adjust that front left sensor again it might bring everything into balance and fix my intermittent lean…


I’m a novice but this system appears to use the sensors we can adjust to get the suspension a rough position as to what is level…but then the system later equalizes the pressures left to right thus negating whatever your initial setting was IF there is a disparity between the spring strength of the left and right.

Thus, perhaps, when you’re figuring out a sag/lean issue, using height adjustments via the sensors may only work when the car first bumps into that height setting…later as the car “settles” itself, you may end up with the same lean, albeit slightly higher off the ground. In my case, I could get the car to sit level after bumping it into high and then back to normal (doesn’t seem to work from low to neutral) but then after driving a while, the driver side front would sag again.

I got a set of 2021 coils from an lx570 that got an aftermarket suspension for cheap so I figured I would start experimenting.

When I noted that the rear right coil is a full 3” taller than the rear left, I suspected that, perhaps due to my slightly heavier truck (with tools and what not), a sag was occurring across the vehicle opposite that one extra tall spring (to the driver side front)…so due to my carrying more tools plus a wilco, a riser, a hitch carrier, etc, I should augment the rear suspension by using the right rear coil on the left rear too.

Sometimes I’m basically “even” left to right and sometimes, after bumping into high and then back to normal and then stopping the car quickly, I’m actually HIGH on the side where I was previously always low.

My suspicion is that I’ve now solved my problem of intermittent sag/lean and now need to adjust my sensors, which were previously adjusted to bias more pressure to the driver side front due to its sag there, back down a bit.

I’ll probably drive it as it is for a bit and see if the system “pressure equalizes left to right” and the fenders in the front are again basically equal distance from the ground left to right. If that occurs I’ll adjust the sensors until when I bump from high back to normal the fenders initially rest, prior to “pressure equalization left to right.” At that point I think I can assume I’ve “sprung” the vehicle appropriately and also adjusted the sensors appropriately.

Or it might not work and I’ll still keep messing with it.

Also, I’ll be, at some point, likely, seeing how 2021 front coils compare to 2011’s (there was a change around 2015) since I’ll be messing with front coil spacers and I have brand new take off’s already.

I’ll do that relatively soon if the current rear left coil replacement doesn’t eliminate my intermittent sag/lean.
 
I replaced the left rear coil with a right rear coil (which is like 3” taller and obviously stronger) in order to give the car a more equal distribution of its weight handling…and now the front left coil, which was always the saggy/lowered spot on the car, is 2-3” taller than the front right…which to me indicates that if I adjust that front left sensor again it might bring everything into balance and fix my intermittent lean…


I’m a novice but this system appears to use the sensors we can adjust to get the suspension a rough position as to what is level…but then the system later equalizes the pressures left to right thus negating whatever your initial setting was IF there is a disparity between the spring strength of the left and right.

Thus, perhaps, when you’re figuring out a sag/lean issue, using height adjustments via the sensors may only work when the car first bumps into that height setting…later as the car “settles” itself, you may end up with the same lean, albeit slightly higher off the ground. In my case, I could get the car to sit level after bumping it into high and then back to normal (doesn’t seem to work from low to neutral) but then after driving a while, the driver side front would sag again.

I got a set of 2021 coils from an lx570 that got an aftermarket suspension for cheap so I figured I would start experimenting.

When I noted that the rear right coil is a full 3” taller than the rear left, I suspected that, perhaps due to my slightly heavier truck (with tools and what not), a sag was occurring across the vehicle opposite that one extra tall spring (to the driver side front)…so due to my carrying more tools plus a wilco, a riser, a hitch carrier, etc, I should augment the rear suspension by using the right rear coil on the left rear too.

Sometimes I’m basically “even” left to right and sometimes, after bumping into high and then back to normal and then stopping the car quickly, I’m actually HIGH on the side where I was previously always low.

My suspicion is that I’ve now solved my problem of intermittent sag/lean and now need to adjust my sensors, which were previously adjusted to bias more pressure to the driver side front due to its sag there, back down a bit.

I’ll probably drive it as it is for a bit and see if the system “pressure equalizes left to right” and the fenders in the front are again basically equal distance from the ground left to right. If that occurs I’ll adjust the sensors until when I bump from high back to normal the fenders initially rest, prior to “pressure equalization left to right.” At that point I think I can assume I’ve “sprung” the vehicle appropriately and also adjusted the sensors appropriately.

Or it might not work and I’ll still keep messing with it.

Also, I’ll be, at some point, likely, seeing how 2021 front coils compare to 2011’s (there was a change around 2015) since I’ll be messing with front coil spacers and I have brand new take off’s already.

I’ll do that relatively soon if the current rear left coil replacement doesn’t eliminate my intermittent sag/lean.
The equalization of pressure between left and right side is documented in the manual for AHC, so I agree it is there, and is also the reason trying to fix a lean with height sensors is a fools errand.

Sounds like you are on the right track. You can also keep in mind, that spring spacers also preload the springs to make them stiffer, so that is another option to attack the issue.

If you are using techstream, the utilities for the AHC ecu allow you to open the gate valves that equalize pressure between left and right on each axle. This could save you the trouble of having to drive the truck around to verify changes.
 
The equalization of pressure between left and right side is documented in the manual for AHC, so I agree it is there, and is also the reason trying to fix a lean with height sensors is a fools errand.

Sounds like you are on the right track. You can also keep in mind, that spring spacers also preload the springs to make them stiffer, so that is another option to attack the issue.

If you are using techstream, the utilities for the AHC ecu allow you to open the gate valves that equalize pressure between left and right on each axle. This could save you the trouble of having to drive the truck around to verify changes.
Good info. I have a tech stream and have downloaded the software…haven’t actually plugged it in and run it yet.

And yes I’ve got spacers on the rear currently along with two right side spring (super easy install, like two bolts in each side).

I’ve got front spacers but haven’t installed yet. They’re a little more involved.

Any idea how long it takes for the “gates” to open up and equalize?
 
Good info. I have a tech stream and have downloaded the software…haven’t actually plugged it in and run it yet.

And yes I’ve got spacers on the rear currently along with two right side spring (super easy install, like two bolts in each side).

I’ve got front spacers but haven’t installed yet. They’re a little more involved.

Any idea how long it takes for the “gates” to open up and equalize?
It’s hard to say. I have a OBD tool that I can run while I’m driving that shows all the AHC actions. The refresh rate isnt great, so I assume you don’t always catch the changes, but I have seen the gate valvaes open when driving with little rhyme or reason to when it happens.

Check this thread for info on that.

Thread 'DIY Smartphone Scan Gauge - OBD Fusion'
DIY Smartphone Scan Gauge - OBD Fusion - https://forum.ih8mud.com/threads/diy-smartphone-scan-gauge-obd-fusion.1269979/
 
update:
I think this solved the lean: replacing the left rear spring.

It’s been about 60 miles since the install and my fender heights have normalized. They seem to always be within 0.5” of each other, even though I haven’t messed with the height sensors since swapping a new right rear spring into the left rear spring perch.


Previously (for basically one drive after the coil replacement) my left front was super high for some reason and it wouldn’t “normalize.” So I bumped it into low, high, and then neutral height to “reset” the AHC computer…since then the fender heights have been normal.

I think sometimes the AHC computer gets itself wonky if you take a corner to hard pulling into a parking spot and immediately turn the car off…or if you bump it into high and then accelerate to above 15-20 mph before it’s complete raised itself…and then, like a rudimentary computer, it keeps itself stuck in that wonky state until you come along and “restart” it by bumping it into low high and then neutral.

I’ll update if the car goes wonky again, but fingers crossed, it was just an issue arising from Lexus deciding that one of the coils should be around 23% taller (albeit skinnier) than the others.

I know not everyone has had the same issue and most people do have that 23% taller spring. All I can say is that perhaps my car sat for a long time before I purchased it and degraded that spring that was catching excess weight. That side is still half an inch lower than the passenger, generally…so by replacing the left rear maybe I put a bandaid on the issue for a while.

Not to get repetitive, but I’m going to try, if it fits, To put brand new 2021 front coils on…and then we will see if the 0.5” differential from passenger to driver goes away.
 
After another 100 miles or so, it appears replacing that left rear spring fixed my issue for now. No more intermittent sag/lean

This morning, I had a 2.5” differential/lean to the driver side front, which was disconcerting…however after an 8th of a mile or so I felt the ahc do some sort of correction…and then after about 35 miles of driving when I measured, everything was back to even…no more sag.

If others have similar issues, my sneaking suspicion is that the following narrative may have happened to my vehicle, and perhaps yours:

-Before I owned it, someone who didn’t drive much owned the car (so it had low miles when I bought it, good times)
-the car sat parked for an extended period of time.
-during that period of time since the right rear coil is 3” taller than the rest, a differential of weight was placed on the opposite (front left) spring.
-slowly the spring and/or some pressurized ahc component gave way due to always having excess weight on it. The coil and/or some ahc part deteriorated.
-once I got the car and added a bunch of weight to the back (I like tools and parts and junk) the issue with the coil and or ahc component was exacerbated.
-the coil was weaker than the others which meant when the ahc equalized pressure left to right, it would sit lower than the others
-the suspension also would, it seems, “leak down” over a period of time via whatever ahc component has deteriorated.
-the car would find itself in a wonky leaned position outside its normal parameters and wouldn’t correct itself via adding pressure unless I cycled through the ahc settings of low high and neutral…then it would even itself out, but, due to the weak spring, as the pressure equalized left to right, it would sag again.

Short term Solution: adding a tougher left rear spring took some pressure off the left front and, now, whatever ahc part has a slow leak doesn’t leak down so far that rhe car’s ahc system finds itself outside its normal parameters so it “resets itself” after driving a short distance and will be able to, likely, keep itself well situated for a long time.

Long term solution: replace the front left coil too…and always run equal strength springs left to right.
 
There still seems to be a bit of “leak down” occurring on the driver side, mostly front. The droop is quite a bit lessened however and shortly after starting the vehicle, while waiting to pull out of my driveway, the ahc system seems correct itself (it lifts the front left and the fenders are back to within 0.5” of one another when I arrive where I’m going).

So the coil replacement/upgrade in the left rear seems to have alleviated most of the ahc lean issue I was having in the driver side front corner…

I will try to replace the front left coil with a 2021 coil (which is a different part number albeit with the same part numbered strut/shock in the center of it).

If that stops the leak down, it’ll be a strong indicator that an lx570 that sits for a while will slowly weaken the front driver coil due to the 3” taller spring in the right rear.

If the leak down continues, it’ll likely be the case that some seal in the ahc system in the driver front has slightly given up the ghost (probably due to that 3” taller spring in the right rear applying more pressure to that front left corner)…and I may end up replacing the globe(s).
 
When I turn ahc “off” it appears the rear will slowly leak down over the course of several days.

While the persistent intermittent lean to the driver side front seems to have alleviated itself, some “leak down” seems to be occurring.

As long as I cycle through high and then back to normal, it seems to keep itself relatively level side to side and front to back (within an inch or so).

Supposedly oem tolerances are something like 0.39”. I’ve ordered new accumulators since the current ones are 10 years or so old and have a bit more than 90k miles.

Supposedly gas slowly leaks out of them or something. I’ve noticed that there’s almost no noticeable difference between sport and comfort mode. Ironically sport seems to provide a better ride…I think because comfort allows a little more “spring” and because my accumulator globes may have lost their “depth”/range due to gas loss, I’m guessing sport tends to keep the suspension from compressing enough to “overshoot” the current range of the accumulators.

As long as I do t hit any moderate bumps, the ahc rides like it seems it should. Noticeably more subdued in its suspension than other vehicles. However if I hit anything more than moderate sized bumps, it appears to be bouncy/harsh.

Similarly, when I bounce down a curb even at very low speeds, the bounce seems a bit harsh.

Interestingly, IMMEDIATELY after pressing the “off” button for AHC, it dropped the front end back down to normal height.

D012A5C2-DF63-4529-82ED-F7B312C447A9.jpeg
 
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