AHC Height Offset Utility How-To (2 Viewers)

[AnyMal]

Every good thread deserves a revival. @NeMal512 - any update? I've got a 1/2" driver side lean I'd like to perfect out... Haven't decided on sensor bracket route or techstream yet (weighing my available time ahead of trip - may just leave it be for now).

What year is your LX?
After moving house, family stuff and my garage still not being in order I’ve been sittin’ sidewayz for a while now.

Since I first wasted a couple of weeks with a non communicative tech stream instance, and the following week or two trying to see if the car would settle evenly I haven’t fully dove into it since. I’m debating disconnecting AHC ECU or relay to fully disable system while leveling the car and “zeroing” in sensors by hand. I do think there is an issue with its programming and I haven’t yet found an AHC ECU reset procedure anywhere. I simply don’t have enough users techstream data to warrant pulling off and troubleshooting height sensors manually but at a middle lock the front read wildly different values, although I do believe they are supposed to be mirrored opposite values (negative for driver side, positive on passenger). If it’s not the sensors sending bad values, or the ECU making an incorrect “leveling” calculation, it may be a bad AHC valve or harness. The former would be impossible for me to diagnose on my own. It could also be a worn shock but it’s too commonly on driver side for that to be an issue and on cars with less than 60k probably not likely to happen anyway.

I made a thread regarding the lean recently and I noted how many LXs Ive seen on the road even new that lean to the driver side. It’s a much bigger issue than it would seem. I am beginning to think that the offset spring height in the rear has a lot to do with it, and frankly I’m not sure why it’s designed that way. The weight of the gas alone is not enough to warrant that much of a Left to Right difference in my view.

I really need some of the forums help or just take the car to a member in TX that can have another look at it. Believe me when I say the dealers have no clue.

 

[TexasPat]

Not having a working laptop, I’m wondering if this is something that a Toyota/Lexus dealership can do. Does anyone know?

 

[radman]

Not having a working laptop, I’m wondering if this is something that a Toyota/Lexus dealership can do. Does anyone know?

I haven't seen any info on the height offset utility in the FSM (does the dealer even really use the FSM??), and always wondered if there's a separate manual for it somewhere.

What's your end goal - level out or lift?

 

[lx200inAR]

I haven't seen any info on the height offset utility in the FSM (does the dealer even really use the FSM??), and always wondered if there's a separate manual for it somewhere.

What's your end goal - level out or lift?

Im sure I’ve read directions from the manual on how to use the offset utility. I’ll post tomorrow.

the gist is that you get the truck close to factory height with physical adjustment of sensors, then you put truck on flat ground and use a jack to level out whichever corner you are working on. This will give you an “after adjust“ value. Then you enter the standard value plus the measured value and those coupled with the after adjust value all are used in an equation the truck uses for offset. I’m sure I’m forgetting some key details, but I know those 3 factors are the important parts.

 

[radman]

Im sure I’ve read directions from the manual on how to use the offset utility. I’ll post tomorrow.

the gist is that you get the truck close to factory height with physical adjustment of sensors, then you put truck on flat ground and use a jack to level out whichever corner you are working on. This will give you an “after adjust“ value. Then you enter the standard value plus the measured value and those coupled with the after adjust value all are used in an equation the truck uses for offset. I’m sure I’m forgetting some key details, but I know those 3 factors are the important parts.

yea, you're right. I believe I was thinking about not ever seeing a general techstream manual that covers all the various screens/tools...

This procedure only works to level out the rig using the obscure measuring methods. If you're wanting to use HOU to lift, you can offset your measured and target measurements up to .8" to achieve the height adjust that you're looking for (described in my original post).
Here are the pages:

 

[lx200inAR]

That’s the one. I was mostly commenting, because I’ve never seen a tutorial that mentions factoring in the after height adjust value, I think this is the key to getting consistent results with the HOU. I know the few times I messed with it, it would rarely accept any inputs I entered, I assume because I wasn’t meeting the requirements of the equation in the FSM.

 

[AnyMal]

Ive done this procedure multiple times and the instructions are still unclear.
It's almost impossible to measure correctly and I still haven't figured what jacking the car is supposed to do although i have some theories.
If youre doing this dont even bother measuring or jacking. Just punch in the INVERSE difference value you want into the field and check visually.
You're really wasting your time if you do more than that.

There is also a section of the service manual pertaining to replacing the height sensors and their installion which is equally dumbfounding.
How exactly are you supposed to set the height sensor within their brackets without having these measurements first is beyond me.
They don't even mention where the sensor arm should be on the bracket if I recall.
It seems like if i wanted to rewrite the spec on stock height, and alignment you could just do as you please and just fix cv angles and be golden.

In my vehicle for example, they are not at all "centered" for stock height, they are kind of all over the place. It makes me think they are slapped on at the factory and there is some super secret AHC ecu setting procedure that is done on first boot that records the relative values and is stuck there for the rest of its existence.

If anyone wants to brainstorm AHC, im down. I will be probably ripping mine apart soon to fix my lean. I am going to mess with the rear springs first though.
Never understood why the rear right hand spring is taller than the rear left. I think its throwing off the rear pressures. I get it for the LC, but makes no sense on the LX or cars with AHC. Doesn't help that you cant read the pressures either like you could on the 100 series.

If AHC compensates for 2,000 lb payload leveling with ease, why do i need a spring rate tension adjustment for a gas tank weighing 145 lbs tops when full that doesnt even sit over the rear axle? Makes no sense at all to me. I will definitely take my individual corner weight readings first though and see where it really shows any imbalance. If anyone has done this with a 16+ LX let me know. You would be saving me a lot time trying to find or buy scales.

Honestly, all of this fooling around really pisses me off. I want to be able to have more control over the suspension.
There isn't even a way to disable the ride height speed limits other than disabling the entire system and I know everyone would love to have that option.
If anyone is savvy in can bus we need to intercept the control relays and build a piggyback kit.
Im tired of being a slave to AHC. I will help fund this as I'm sure many others would.

 

[radman]

Just punch in the INVERSE difference value you want into the field and check visually.
You're really wasting your time if you do more than that.

you hit the nail on the head. However, sometimes you have to stay near the FSM standard values (3.9 or 3.7) rather than something crazy like 18.0 and 17.5 (to get .5" lift).

How exactly are you supposed to set the height sensor within their brackets without having these measurements first is beyond me.
They don't even mention where the sensor arm should be on the bracket if I recall.

same.

they are not at all "centered" for stock height, they are kind of all over the place.

same. I break all the 10mm nuts loose, and then use a stick to measure the 4 corners. Hand loosen/tighten the sensor and try to get close to my stick mark (waiting 30 seconds after movements), and then use HOU to fine tune if needed.

If AHC compensates for 2,000 lb payload leveling with ease, why do i need a spring rate tension adjustment for a gas tank weighing 145 lbs tops when full that doesnt even sit over the rear axle?

I broke 8,000lbs on a certified scale, 5k of that on the rear axle. I love the system, and don't really have a huge desire to change it or turn parts of it off.

Never understood why the rear right hand spring is taller than the rear left.

interesting note for my rear. If I adjust the driver side, it affects the passenger side. No one has ever been able to confirm if i'm isolated or if it's the same on others, but my rears are not isolated like my fronts.

I'd be open to dive back into this, but I've forgotten a lot of it and some of you guys have picking up the slack!

 

[AnyMal]

you hit the nail on the head. However, sometimes you have to stay near the FSM standard values (3.9 or 3.7) rather than something crazy like 18.0 and 17.5 (to get .5" lift).

same.

same. I break all the 10mm nuts loose, and then use a stick to measure the 4 corners. Hand loosen/tighten the sensor and try to get close to my stick mark (waiting 30 seconds after movements), and then use HOU to fine tune if needed.


I broke 8,000lbs on a certified scale, 5k of that on the rear axle. I love the system, and don't really have a huge desire to change it or turn parts of it off.


interesting note for my rear. If I adjust the driver side, it affects the passenger side. No one has ever been able to confirm if i'm isolated or if it's the same on others, but my rears are not isolated like my fronts.

I'd be open to dive back into this, but I've forgotten a lot of it and some of you guys have picking up the slack!

Hell yeah brother, im in Houston all the time bootleg techstream on deck LOL.
What would really be interesting is swapping ECUs with someone and seeing what the truck does.

As far as can-bus spoofing someone like @linuxgod needs to help because these systems are all linux based and im not savvy enough at all to read or reverse engineer it.
(I'm assuming you're a Linux ENG/DEV)

What really has me thinking right now is how absolutely easy it would be to fully replace height sensors with artificial voltage manipulation.
AHC system itself is so mechanically simple ( I mean that in the best way) that there are multiple points where I can see potential for bypassing / tricking the system.
Once the AHC nut is cracked I think we will all be absolutely crushing some whole foods parking lots.

I had my car in H when loading something at Home Depot and a guy stopped me to ask what car it was.
I answered him and his reply was a bewildered "Thats a Lexus?!" Yeah buddy... Its a Lexus alright. Best car in the world.

 

[lx200inAR]

you hit the nail on the head. However, sometimes you have to stay near the FSM standard values (3.9 or 3.7) rather than something crazy like 18.0 and 17.5 (to get .5" lift).

same.

same. I break all the 10mm nuts loose, and then use a stick to measure the 4 corners. Hand loosen/tighten the sensor and try to get close to my stick mark (waiting 30 seconds after movements), and then use HOU to fine tune if needed.


I broke 8,000lbs on a certified scale, 5k of that on the rear axle. I love the system, and don't really have a huge desire to change it or turn parts of it off.


interesting note for my rear. If I adjust the driver side, it affects the passenger side. No one has ever been able to confirm if i'm isolated or if it's the same on others, but my rears are not isolated like my fronts.

I'd be open to dive back into this, but I've forgotten a lot of it and some of you guys have picking up the slack!

Maybe i can spend some time on it this weekend. I don't have a flat spot to test at my house, so i have to go somewhere else to tinker with it.

I don't think it's as "witch crafty" as it's being made out here.

I'll save my theories on how it all works after playing with it more, as sometimes i run my keyboard too much without having a clue what i'm talking about.

My quick unscientific theory on why both sides might adjust when you adjust one of the corners is that i've read in 100 series AHC threads that the height chosen by the system is based on an average of the two height sensors. Also, the system has a gate valve that balances the two sides out on each axle. Possibly what is happening is you enter a new height so that side gets more pressure, then they system decides to use the gate valve to balance the two sides and you end up getting both sides raised a little rather than one side raised a lot. If this is the case then doing the offset on both wheels at the same time would be the best course of action.

It could be either or both of these factors, or neither for that matter.

I agree there is a lot that we don't know about the system. But there are only so many sensors and physical inputs It can't be that complicated, it would be nice to know what triggers each of the system adjustments. To my earlier point, we know the gate valve is there between each corner on an axle, but we don't know what factors trigger it opening. Does it open after every height adjust to balance, or just when it senses too big a difference in height between the two axles, or something else, or all of the above.

 

[lx200inAR]

Hell yeah brother, im in Houston all the time bootleg techstream on deck LOL.
What would really be interesting is swapping ECUs with someone and seeing what the truck does.

As far as can-bus spoofing someone like @linuxgod needs to help because these systems are all linux based and im not savvy enough at all to read or reverse engineer it.
(I'm assuming you're a Linux ENG/DEV)

What really has me thinking right now is how absolutely easy it would be to fully replace height sensors with artificial voltage manipulation.
AHC system itself is so mechanically simple ( I mean that in the best way) that there are multiple points where I can see potential for bypassing / tricking the system.
Once the AHC nut is cracked I think we will all be absolutely crushing some whole foods parking lots.

I had my car in H when loading something at Home Depot and a guy stopped me to ask what car it was.
I answered him and his reply was a bewildered "Thats a Lexus?!" Yeah buddy... Its a Lexus alright. Best car in the world.

I've considered this before, and I agree, grabbing and faking the voltage from the height control sensors has to be the easiest way to manipulate the system. I don't think CAN manipulation is an option. I know the height sensor data is available on CAN BUS, but the Suspension Control ECU takes inputs from the sensors and outputs to all the actuators and controls the AHC pump. So I believe it's only available on the CAN BUS for TechStream. There would be no way to hijack the CAN signal and manipulate since the Suspension Control ECU isn't "using" the CAN data, it's just providing it.

 

[AnyMal]

Thanks @lx200inAR for your input.

I see where youre going with this but at the very least, is the AHC ECU not receiving wheel speed telemetry to block high mode and enter highway low for example?
Not that spoofing the wheel speed is a safe idea, but it could be switched on and off and just be an inline module to the AHC ECU.
I believe its the blue and white cable only and the other output cabling could be left untouched. (stuff that controls the pumps and reservoirs and dampers).
It could be something so simple as a constant 5MPH spoof relay and could be switched back to stock input.

Thats whats in my understanding at the moment. Hoping for more info and opinions.

I've considered this before, and I agree, grabbing and faking the voltage from the height control sensors has to be the easiest way to manipulate the system. I don't think CAN manipulation is an option. I know the height sensor data is available on CAN BUS, but the Suspension Control ECU takes inputs from the sensors and outputs to all the actuators and controls the AHC pump. So I believe it's only available on the CAN BUS for TechStream. There would be no way to hijack the CAN signal and manipulate since the Suspension Control ECU isn't "using" the CAN data, it's just providing it.

 

[AnyMal]

Maybe i can spend some time on it this weekend. I don't have a flat spot to test at my house, so i have to go somewhere else to tinker with it.

I don't think it's as "witch crafty" as it's being made out here.

I'll save my theories on how it all works after playing with it more, as sometimes i run my keyboard too much without having a clue what i'm talking about.

My quick unscientific theory on why both sides might adjust when you adjust one of the corners is that i've read in 100 series AHC threads that the height chosen by the system is based on an average of the two height sensors. Also, the system has a gate valve that balances the two sides out on each axle. Possibly what is happening is you enter a new height so that side gets more pressure, then they system decides to use the gate valve to balance the two sides and you end up getting both sides raised a little rather than one side raised a lot. If this is the case then doing the offset on both wheels at the same time would be the best course of action.

It could be either or both of these factors, or neither for that matter.

I agree there is a lot that we don't know about the system. But there are only so many sensors and physical inputs It can't be that complicated, it would be nice to know what triggers each of the system adjustments. To my earlier point, we know the gate valve is there between each corner on an axle, but we don't know what factors trigger it opening. Does it open after every height adjust to balance, or just when it senses too big a difference in height between the two axles, or something else, or all of the above.

Didnt see this...

The 100 shares a rear sensor, and I believe works that way but the 200 has independent sensors and a fancier multi way valve assembly. Its like a 4 way matrixing valve controller. @TeCKis300 will know way more here on that.

My theory on the 200 AHC is that its constantly working on individual corner pressures **which techstream is not showing us** to achieve level AGAINST the corner height sensor readings. That way it is both fully mechanical and each height level is a simple function of what pressure the system needs to lift the shock assembly to reach the voltage value of the sensor. There is some internal calibration to the AHC ECU that knows for the GVWR what those pressures should be and what the damping rate pressures are to be sustained for the ride comfort setting needed.

That is my armchair analysis at this point, but i need more time with the system.

 

[tbisaacs]

Why the desire to lock in high other than to flex on the haters? It rides significantly worse in my opinion.

 

[lx200inAR]

Didnt see this...

The 100 shares a rear sensor, and I believe works that way but the 200 has independent sensors and a fancier multi way valve assembly. Its like a 4 way matrixing valve controller. @TeCKis300 will know way more here on that.

My theory on the 200 AHC is that its constantly working on individual corner pressures **which techstream is not showing us** to achieve level AGAINST the corner height sensor readings. That way it is both fully mechanical and each height level is a simple function of what pressure the system needs to lift the shock assembly to reach the voltage value of the sensor. There is some internal calibration to the AHC ECU that knows for the GVWR what those pressures should be and what the damping rate pressures are to be sustained for the ride comfort setting needed.

That is my armchair analysis at this point, but i need more time with the system.

I don't think this is true. Where is the system getting the system pressures from? There is no mention of there being a pressure sensor anywhere in the system except at the pump. I think the system uses the height sensors to determine if there is enough pressure and only uses the system pressure to determine if the system is functioning, meaning it only triggers anything if the pressure is too low or too high.

The height control is based on 6 valves (not including pump and accumulator valves) 1 for each corner and 1 gate valve between the corners on each axle.

Also, my reference to the averaging of sensors was in reference to the front end on the 100 series where there are two height measurements.

 

[lx200inAR]

Why the desire to lock in high other than to flex on the haters? It rides significantly worse in my opinion.

I agree, i really have no desire for the system to function any differently when moving. My only curiosity would be using the system to auto level the truck when parked. WHich is why it's not super high on my actual list of concerns.

 

[tbisaacs]

I agree, i really have no desire for the system to function any differently when moving. My only curiosity would be using the system to auto level the truck when parked. WHich is why it's not super high on my actual list of concerns.

i think the killer feature would be a switch in back to kneel the truck while off like a Range Rover. I know there is the switch to automatically every time truck is turned off - but I don’t leave it on all the time.

 

[linuxgod]

Hell yeah brother, im in Houston all the time bootleg techstream on deck LOL.
What would really be interesting is swapping ECUs with someone and seeing what the truck does.

As far as can-bus spoofing someone like @linuxgod needs to help because these systems are all linux based and im not savvy enough at all to read or reverse engineer it.
(I'm assuming you're a Linux ENG/DEV)

What really has me thinking right now is how absolutely easy it would be to fully replace height sensors with artificial voltage manipulation.
AHC system itself is so mechanically simple ( I mean that in the best way) that there are multiple points where I can see potential for bypassing / tricking the system.
Once the AHC nut is cracked I think we will all be absolutely crushing some whole foods parking lots.

I had my car in H when loading something at Home Depot and a guy stopped me to ask what car it was.
I answered him and his reply was a bewildered "Thats a Lexus?!" Yeah buddy... Its a Lexus alright. Best car in the world.

Ask @TeCKis300 as he's done an AHC sensor lift on his rig. If your LX is unlevel it's possible one of the sensors is misaligned.

 

[lx200inAR]

I don't think this is true. Where is the system getting the system pressures from? There is no mention of there being a pressure sensor anywhere in the system except at the pump. I think the system uses the height sensors to determine if there is enough pressure and only uses the system pressure to determine if the system is functioning, meaning it only triggers anything if the pressure is too low or too high.

The height control is based on 6 valves (not including pump and accumulator valves) 1 for each corner and 1 gate valve between the corners on each axle.

Also, my reference to the averaging of sensors was in reference to the front end on the 100 series where there are two height measurements.

In looking at the FSM for the 100 series. It appears to only have one sensor as well. From memory I don't believe techstream reports pressures for each corner but actually for each axle. I wonder if it takes a pressure reading while only the front leveling valves are open and another reading while only the rear valves are open to report a value for each field in Techstream. From what little i've read on the 100 series, the field is similar to 200 series in that it only shows values during pump activation and that the numbers are not consistent and you need to check multiple times to get a somewhat accurate reading.

 

[lx200inAR]

And more thoughts about how the AHC ECU may use the pressure sensor. It may store a pressure reading during filling the accumulator, or maybe even periodically checks the pressure in the accumulator by opening the accumulator valve with pump activated and all leveling valves closed. There are definitely references in the manual to the accumulator valve opening or not depending on the pressure in the accumulator. I only skimmed the 100 series manual but it goes into depth a little more about when the pump or the accumulator are used to raise the vehicle, depending on vehicle speed. For example, it explains that if the vehicle is going over 16mph, only the pump is used to raise the vehicle. This goes against speculation recently in another thread that the accumulator is used to maintain height when the system goes back up after dropping when traveling over 62mph.

It would be very interesting to see all this in action. I'd love to be able to see a debug dump of all the sensor inputs and control outputs from the AHC ECU.