LX570 AHC height modifications (lift it!) (6 Viewers)

[lx200inAR]

One caution to using too much spring, is the system may spit out AHC fluid from the reservoir, when going to low position. The system basically continues to evacuate AHC fluid, and if Low is hard or unattainable because of too my physical spring, more of the normally pressured fluid volume in the accumulators will go to the reservoir. And it may never reach low position.

Can you explain this part? I was under the impression that the weight of the truck pushing back on the actuators (shocks) was what drove fluid back into the reservoir. If the springs stop the truck from lowering, won't there not be any pressure pushing fluid back into the reservoir?

Only asking for academic reasons, I won't be changing my springs any time soon.

 

[beer]

How far did you move the front sensors?

All the way down. I'll be getting an alignment this week. Gained about an inch on each front side when measuring floor-to-fender. I still have a small amount of rake as the rear measurements are a bit under 1" higher than the front measurements.

 

[victor910]

No.Do you know how to fix differences between left and right side?

 

[TeCKis300]

Can you explain this part? I was under the impression that the weight of the truck pushing back on the actuators (shocks) was what drove fluid back into the reservoir. If the springs stop the truck from lowering, won't there not be any pressure pushing fluid back into the reservoir?

Only asking for academic reasons, I won't be changing my springs any time soon.

You're on the right track. It would normally be the weight of the truck pushing fluid out of the shock bodies that drives fluid back to the reservoir. But the system is calibrated that even in the Low kneel position, that AHC and the accumulators are still bearing some small portion of the vehicles weight. For the sake of discussion, let's call this 20% of the weight. So the accumulators are still pressurized to a degree (and diaphragms are pushed in, holding more volume of fluid) by the weight of the truck.

With too much physical spring, it may bear potentially the full weight of the car before that low position is even reached. This allows AHC accumulators to "droop" more than normal, potentially holding 0% of the weight of the truck. Basically this has the diaphragms in the accumulators fully expanded, reducing the fluid volume held in each of the 5 accumulators to very little - and driving excess volume of fluid into the reservoir where it may overflow.

 

[lx200inAR]

You're on the right track. It would normally be the weight of the truck pushing fluid out of the shock bodies that drives fluid back to the reservoir. But the system is calibrated that even in the Low kneel position, that AHC and the accumulators are still bearing some small portion of the vehicles weight. For the sake of discussion, let's call this 20% of the weight. So the accumulators are still pressurized to a degree (and diaphragms are pushed in, holding more volume of fluid) by the weight of the truck.

With too much physical spring, it may bear potentially the full weight of the car before that low position is even reached. This allows AHC accumulators to "droop" more than normal, potentially holding 0% of the weight of the truck. Basically this has the diaphragms in the accumulators fully expanded, reducing the fluid volume held in each of the 5 accumulators to very little - and driving excess volume of fluid into the reservoir where it may overflow.

I see what you are saying, the ecu will open the leveling valves to lower the truck, but if it can’t reach L, eventually the pressure will drop below be provided by the gas pressure in the accumulators and the accumulators will fully evacuate even though the truck won’t lower because it’s supported by the springs.

Have you ever seen this in a 200? The tank looks so big, and “full” is only like 30-40% full.

Edit: I made a minor edit above to correct conceptually my account of system pressure

 

[borfoo3]

A bit of a side question here..
I'm having a problem trying to access the AHC ECU in tech stream (using VXDiag VCX NANO) for my 2021 Land Cruiser 200.. Basically it does not shop up at all under the ECU table.
I'm suspecting that I'm not choosing the correct vehicle version in the 'vehicle connection wizard' dialogue box I can't seem to find the correct vehicle version.. any ideas? Which region/ area are you using?

 

[lx200inAR]

Most people here are probably using North America and selecting the LX570. In the USA, only the Lexus has AHC. I would think your trouble stems from either the wrong region/model like you are suggesting, or possibly not a new enough version of Techstream.

 

[AnyMal]

There are multiple ways the AHC ECU could be regulating pressure or even fluid volume per corner if thats what its designed to do. Just do some experimentation and it would answer many questions in this thread and some accusations. Luckily i have done this for you.
All of this can happen without any sensor involvement but just through clever engineering and some math.
When you have lot of known and fixed variables, this is exactly when computation and data can be of huge benefit in building systems like this.
If you take some time to do your homework, you can see a whole bunch of evidence the ECU is making calculated decisions.

Also, the truck does not just level laterally when being driven. AHC is not KDSS. Thats a gross oversimplification and is just wrong.
All one would have to do to disprove this dangerous misinformation is to set all sensors to opposite values, Left hand set front down and rear up, right side set front up and rear down. Your truck will be pressurized to meet the normative sensor value and remain there. AHC does not damp by fluid dynamic LEFT/RIGHT or X. AHC redirects shock valving to pre loaded dampers, 2 in front one in rear axle per corner.


Here are some examples of basic computation values the ECU could be taking into account.

Time it takes to lift to reach where sensor needs to be (timeout lockout)
Time the pump is running (fluid volume known as well as single pressure sensor account)
Sensor value when loaded versus where the sensor value should be in L, N or H against last known pressurized height value
Sensor value not changing despite pump adding pressure (overload condition)

In regards to leveling if you pay attention, you can see some calculations affecting decisions.
Since we know both axles lift simultaneously, and we can set the truck to be out of level on either axle (although there is a built in limit as well) we can deduce that shocks can be independently adjusted and pressurized to height.

This can be so easily achieved by just lifting both valves (left/right) open, and just shutting one down earlier than the other.
Also it could know pump run time or calculated fluid volume and run for the adjusted snesor sum of getting to level either way since the truck has no way to know if its overloaded one one corner only or just off kilter. We can never really know what its doing but HOU is extremely indicative that there are more parameters that need to be met other than just reaching a sensor voltage value.


I could go on and on and i really don't want to have a debate but i implore you to go back and perform my troubleshooting guide if you want to resolve any issues with AHC. Anyone running a lift and either out of level or failing to raise or lock in H could potentially be compromising themselves in some unknown area. I personally wouldnt run my truck that way out of my sheer OCD but also, we dont know what we dont know, and its best to have full operation anyway.

 

[lx200inAR]

There are multiple ways the AHC ECU could be regulating pressure or even fluid volume per corner if thats what its designed to do. Just do some experimentation and it would answer many questions in this thread and some accusations. Luckily i have done this for you.
All of this can happen without any sensor involvement but just through clever engineering and some math.
When you have lot of known and fixed variables, this is exactly when computation and data can be of huge benefit in building systems like this.
If you take some time to do your homework, you can see a whole bunch of evidence the ECU is making calculated decisions.

Also, the truck does not just level laterally when being driven. AHC is not KDSS. Thats a gross oversimplification and is just wrong.
All one would have to do to disprove this dangerous misinformation is to set all sensors to opposite values, Left hand set front down and rear up, right side set front up and rear down. Your truck will be pressurized to meet the normative sensor value and remain there. AHC does not damp by fluid dynamic LEFT/RIGHT or X. AHC redirects shock valving to pre loaded dampers, 2 in front one in rear axle per corner.


Here are some examples of basic computation values the ECU could be taking into account.

Time it takes to lift to reach where sensor needs to be (timeout lockout)
Time the pump is running (fluid volume known as well as single pressure sensor account)
Sensor value when loaded versus where the sensor value should be in L, N or H against last known pressurized height value
Sensor value not changing despite pump adding pressure (overload condition)

In regards to leveling if you pay attention, you can see some calculations affecting decisions.
Since we know both axles lift simultaneously, and we can set the truck to be out of level on either axle (although there is a built in limit as well) we can deduce that shocks can be independently adjusted and pressurized to height.

This can be so easily achieved by just lifting both valves (left/right) open, and just shutting one down earlier than the other.
Also it could know pump run time or calculated fluid volume and run for the adjusted snesor sum of getting to level either way since the truck has no way to know if its overloaded one one corner only or just off kilter. We can never really know what its doing but HOU is extremely indicative that there are more parameters that need to be met other than just reaching a sensor voltage value.


I could go on and on and i really don't want to have a debate but i implore you to go back and perform my troubleshooting guide if you want to resolve any issues with AHC. Anyone running a lift and either out of level or failing to raise or lock in H could potentially be compromising themselves in some unknown area. I personally wouldnt run my truck that way out of my sheer OCD but also, we dont know what we dont know, and its best to have full operation anyway.

I'm going to pretend like we are having a normal conversation and not one where you are making personal attacks at my career for some reason, and respond accordingly.

Have you seen the manual for AHC? It explains very specifically that there is a gate valve on each axle between corners and that it's purpose is to balance the pressure between the left and right side. I'm not inferring that from any tests, it's right there in the documentation. (I do agree it's not used for any stability type control as I stated in a post not directed at you that I've since edited, since that valve being open would negate the affects of the center suspension control cylinder)

2) Gate Valve
This valve is provided for both the front and rear sides. This valve opens and closes the fluid passage to
both the left and right leveling valves. Normally, the fluid passage is closed. The fluid passage opens in
accordance with signals from the suspension control ECU, thereby balancing the fluid pressure for both
the left and right gas chambers.

It sounds like you aren't considering the fact that the system responds differently when parked in your driveway and when the truck is in motion. I don't really understand why you are hung up on the ability to move one corner when parked. I've never said that wasn't possible. But at some point the truck opens the gate valves and the balance between the sides of an axle are restored, so the fact that it can doesn't really matter. Obviously, it's not ideal to have different pressures at each corner as it will cause unplanned shifts in height every time the gate valve is open. This means it's more important to have the pressure balance between the left and right side than it is to have no lean (assuming there is one when the pressure is balanced). In a perfect world you'd have even pressure and no lean, but if you have to pick one or the other, you want even pressure.

Lets assume the truck is measuring pressure at each corner, why would it? And if it did, why would Toyota hide that data from Techstream? In the 100 you got 2 values for pressure (3 including the accumulator) because the truck filled all three sections separately, so it could report how much pressure it took to fill all three. All your guesses at how it would calculate pressure are mildly plausible and on an even simpler level the system could just record the pressure from the pump sensor for each corner when it closes the leveling valve for that corner. Here's where all that gets tricky through, those methods really only work when the truck is going up. When the truck is going down, it's a whole different equation, that gets far more inaccurate.

Back to the "WHY?" We already know the system makes decision based on sensor heights (and for all aspects of the AHC/AVS system, inputs from all the other sensors explained in the manual). We know this is true because you can get the system out of whack moving the sensors. If the truck was making decisions based on pressure, it wouldn't' allow you to go to heights that put the system pressure. off. At the very least, wouldn't Toyota trigger a DTC if it knew the pressures were off to get to a certain height?

I'll add, I believe we aren't really arguing too far a different point. We both know the pressure needs to be in a certain range for the system to function properly, although you seem to argue against that regularly when you keep trying to say that you can level out the truck with AHC or HOU. You keep making this point even after you've proven that the way to level the truck was to change out your spring on one side to change the balance between AHC and springs. So I don't really know where the disconnect is. I should maybe restate more clearly, I know the truck requires a certain pressure range to function properly (primarily so that the spring rate switching valves and actuators are functioning as designed), but the ECU doesn't make decisions based on pressure. It will freely let you muck up the pressure in the AHC system with no complaints and happily go about it's business giving a crappy ride.

As far as your troubleshooting guide, I certainly don't fault the highlights of making sure everything in the system is healthy. The only minor error I see is that you only offer doing an AHC lift as a possible solution. If the truck is already too high and that was causing a poor ride, then lifting more isn't going to fix anything, Luckily you can only go 2 ways, so if lifting makes it worse it's no problem to undo that, and even try lowering to see if that improves it. But all this isn't new info, it was worked out years ago on the 100 series and the general premise of having your pressure in the correct operating range was no secret.

 

[TeCKis300]

Not looking to take sides here and partly afraid to wade in. Well, not really, but just know my only prerogative is understanding so we can scheme on how to modify!

The AHC system doesn't rather care about volume or pressure. Actually has no ability to meter volume and would not be a great strategy when there's so many variables (accumulator or spring wear) that effect it. It does measure pressure but over at the pump/reservoir, where it's likely meant to monitor more for pump/system protection.

The main PV in the PID loop (read main variable in the feedback loop) is the height sensors.

 

[AnyMal]

Not looking to take sides here and partly afraid to wade in. Well, not really, but just know my only prerogative is understanding so we can scheme on how to modify!

The AHC system doesn't rather care about volume or pressure. Actually has no ability to meter volume and would not be a great strategy when there's so many variables (accumulator or spring wear) that effect it. It does measure pressure but over at the pump/reservoir, where it's likely meant to monitor more for pump/system protection.

The main PV in the PID loop (read main variable in the feedback loop) is the height sensors.

The point is Teckis, it absolutely cares. Its built to regulate pressure in the damping, and otherwise like you said would be dangerous not to monitor from a safety standpoint. If all values were satisfied, but a pressure calculation not within tolerance it would be a good place to stop the system from running.
How that happens or wether its visible or not is not another story. Fluid volume etc is just one of many ways that things could be monitored, thats all.
It does not have to be measured, and would be far from the realm of possibility to be calculated.

 

[TN LX570]

Up, Up, Down, Down, Left, Right, Left, Right, B, A, Start..levels right up In techstream.

 

[nwfl4runner]

so here's a question: when I am driving around town and come to a stop, often the front driver side will raise itself to level. I've assumed it's normal, but is that particular issue something that can be addressed with either the sensors or the HOU? And my entire front/rear suspension/globes are new, fluid fresh.

 

[radman]

so here's a question: when I am driving around town and come to a stop, often the front driver side will raise itself to level. I've assumed it's normal, but is that particular issue something that can be addressed with either the sensors or the HOU? And my entire front/rear suspension/globes are new, fluid fresh.

This (the constant self-leveling) drove one of the members crazy, and he ultimately sold the truck because of it (overly OCD maybe?). There's no way to stop the self-leveling other than pressing the "off" button, which I believe will automatically come back on if you drive over 20mph.

One interesting thing that I've observed is that my front will normally auto-adjust; however, if i have aux tank full and my spare tire on (100lbs), the rear does all the leveling.

 

[tbisaacs]

Y'all need to zip up and put your tools back in your pants and take a break from Mud for a few days. Bunch of strangers rage typing at each other on the internet. I'm here for the cruisers.

 

[Romer]

I cleaned up a few posts and will shut this thread down if you make me put my drink down and get out of my chair to moderate this thread

As a poster you may be convinced you know whats going on and are an expert. You may counter respectfully with your opinion. You can not insult others

And after you have clearly made your point . . . MOVE ON. These debates don't help and detract from everyone else here

 

[beer]

Anything look off here? I'm still not convinced my suspension is functioning as intended, so just trying to check things off in the proper order. No current codes were thrown. Have recently done globes, fluid, sensor lifted front, and alignment. Dealer said no issues at 95k service and about to do 100k.

 

[grinchy]

Anything look off here? I'm still not convinced my suspension is functioning as intended, so just trying to check things off in the proper order. No current codes were thrown. Have recently done globes, fluid, sensor lifted front, and alignment. Dealer said no issues at 95k service and about to do 100k.

View attachment 2855646

Are you using LT tires? If so up the pressure 3 psi.

 

[LOTFB]

Are you using LT tires? If so up the pressure 3 psi.

Love my 35s

 

[beer]

Are you using LT tires? If so up the pressure 3 psi.

Yes, 285/75R17 Cooper Discoverer AT3 XLT. Looking back, I see 35psi is what was prescribed for this tire+vehicle combo, but I've been running 38psi for some reason. Will test a range of pressures and see if anything changes.