The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (4 Viewers)

[IndroCruise]

Good morning group from an icy Kentucky. I'm currently working from home and have a great deal of extra time. So, having recently purchased a 1998 Lexus LX 470 with 237K on it I'm still deep in the throughs of frenzied research and the honeymoon period.

The truck is in remarkably great shape for its age and had a great service record and at the time was the only one within 500 miles of me in my price range. So I made the plunge and she's ours. We are the fourth owner and she was maintained flawlessly according to Lexus records up until about 10k ago.

I don't know about you guys but I've wanted a Land Cruiser since I was a young man (I'm 53 now) and ironically could only afford one many years later... I digress. I give a whole diatribe on how I chose this truck and why in another thread. That being said, I'm going through her pretty thoroughly (When I say I that's my very trusted mechanic and I). I'll do the body, suspension, power steering flush, heater t's etc.. I'll have him do the timing belt, pump, serpentine etc.

It's at his shop now being checked out for a random "fire and no start" issues early this week (it started as soon as AAA got here of course but hey its free so I had them drop it there). I was taking it there anyway to be checked out (check engine on PO says it's an O2 sensor). I've ordered an OBD2 reader that should be in any day.

All that being said here is my question:

The AHC currently goes into the N and L position. It will not go into H. It seems to be working. You can hear the pumps and it leveling. The level in the reservoir changes from L to N. But, will not go any higher. It even changes height when in L once moving. Just no H. So, that would tell me the system is "working" somewhat.

Question 1. If I can't do a graduation test where do I begin? Is it just low? Could I add fluid see if it raises then do a flush later? Just kind of don't know where to start? All the information I've seen starts with assuming everything is working - i.e. the graduation test. The fluid is expensive as you all know and I don't just want to go throwing it away.

Question 2: It seems to ride just fine now - actually very nice. Telling me the globes and system is again, "somewhat functional." What is the harm in not addressing the AHC? I have timing belt and other "essential maintenance" to get though in the next couple of months. Can this wait for warmer weather assuming simple adding fluid doesn't fix it? Can it wait on my list? Looks like I may be dealing with the known "fuse box" issue also...we'll see what the mechanic says today. Just trying to pick my battles as I rides just fine today. There is a lot of rust around the components and I'd like to soak them down for the next month with some WD40 and penetrating lubricant before I attempt to turn the first wrench. Thoughts?

Suggest that your starting point is Techstream.

If you have not got Techstream or need help in setting it up the following thread provides excellent guidance:
How-To: TechStream In 5 Minutes - https://forum.ih8mud.com/threads/how-to-techstream-in-5-minutes.1034923/

The point is that you really need to know your AHC neutral pressures -- just make sure that there is adequate genuine fluid in the AHC tank, at least between the MAX/MIN lines, then measure AHC pressures after moving from "N" to "LO" then back to "N".

Various causes of your 'symptoms' are possible but a commonly this is indicative of 'globes' being at excessive pressure, due either to (1) huge loads in the vehicle, or more likely, (2) old age meaning tired front torsion bars and tired rear springs such that nowadays the AHC is carrying a greater share of the vehicle weight than it should. Either way, in this condition the system will refuse to lift to "HI" because pressures increase even further when the vehicle raises to "HI". The 'fix' at the front is easy and cheap -- turn both torsion bar adjusters equal turns clockwise (as seen when looking up at the bolt head) until front AHC pressures are in the specified range. After making this adjustment check and equalise front cross-level. The rear is a bit more complicated -- rear overpressure is not adjustable and usually requires correction at least by spacers, or better still, replacement rear springs. Suggest start at the front and go from there.

If your mechanic is new to AHC, explain that on an AHC vehicle, torsion bar adjustment is NOT used for adjusting the 'ride height' of the vehicle. (Height Control Sensor adjusters are used to adjust 'ride height').

If you have not seen them, also suggest having a look at the “Cheat Sheet”, video and explanation at this link:
Builds - The YotaMD Build - Cypress - https://forum.ih8mud.com/threads/the-yotamd-build-cypress.1184210/page-9#post-13383404

And also suggest go back to the begining “ABC’s of AHC” for a refresher:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520

Note that the 'graduation test' comes last when checking out AHC -- (1) cross-level, (2) get hub-to-fender distances right, (3) get AHC neutral pressures right, (4) check overall condition of 'globes' using 'graduation test' at correct AHC neutral pressures.

 

[Todd Atchison]

Suggest that your starting point is Techstream.

If you have not got Techstream or need help in setting it up the following thread provides excellent guidance:
How-To: TechStream In 5 Minutes - https://forum.ih8mud.com/threads/how-to-techstream-in-5-minutes.1034923/

The point is that you really need to know your AHC neutral pressures -- just make sure that there is adequate genuine fluid in the AHC tank, at least between the MAX/MIN lines, then measure AHC pressures after moving from "N" to "LO" then back to "N".

Various causes of your 'symptoms' are possible but a commonly this is indicative of 'globes' being at excessive pressure, due either to (1) huge loads in the vehicle, or more likely, (2) old age meaning tired front torsion bars and tired rear springs such that nowadays the AHC is carrying a greater share of the vehicle weight than it should. Either way, in this condition the system will refuse to lift to "HI" because pressures increase even further when the vehicle raises to "HI". The 'fix' at the front is easy and cheap -- turn both torsion bar adjusters equal turns clockwise (as seen when looking up at the bolt head) until front AHC pressures are in the specified range. After making this adjustment check and equalise front cross-level. The rear is a bit more complicated -- rear overpressure is not adjustable and usually requires correction at least by spacers, or better still, replacement rear springs. Suggest start at the front and go from there.

If your mechanic is new to AHC, explain that on an AHC vehicle, torsion bar adjustment is NOT used for adjusting the 'ride height' of the vehicle. (Height Control Sensor adjusters are used to adjust 'ride height').

If you have not seen them, also suggest having a look at the “Cheat Sheet”, video and explanation at this link:
Builds - The YotaMD Build - Cypress - https://forum.ih8mud.com/threads/the-yotamd-build-cypress.1184210/page-9#post-13383404

And also suggest go back to the begining “ABC’s of AHC” for a refresher:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520

Note that the 'graduation test' comes last when checking out AHC -- (1) cross-level, (2) get hub-to-fender distances right, (3) get AHC neutral pressures right, (4) check overall condition of 'globes' using 'graduation test' at correct AHC neutral pressures.

Thank you guys so much. I’ll do my part and dig into the treads. I’d like to keep the system if possible. I will be battling rusty components from the get go. Going start by keeping the miles down on her and slowly bringing things back into spec. I have an ODB2 sensor on the way.

 

[IndroCruise]

Thank you guys so much. I’ll do my part and dig into the breads. I’d like to keep the system if possible. I will be battling rusty components from the get go. Going start by keeping the miles down on her and slowly bringing things back into spec. I have an ODB2 sensor on the way.

Just so you don’t get a shock ….

Be aware that if you cannot see new ‘globes’ in the recent history of the vehicle, it may be on the horizon and may be revealed by the HI/LO graduation check when you get to that point, where 14 graduations = as new ‘globes; 7 graduations = time to change out ‘globes’.

Usually the ride will become harsh towards 7 graduations which indicates that 'globes' have lost much of their nitrogen pressure.

Also be aware that correct AHC pressures and correct AHC operation, “LO” > “N” > “HI”, tells you nothing about ‘globe’ condition.

Hope all goes well and that you enjoy the truck!!

 

[IndroCruise]

Just so you don’t get a shock ….

Be aware that if you cannot see new ‘globes’ in the recent history of the vehicle, it may be on the horizon and may be revealed by the HI/LO graduation check when you get to that point, where 14 graduations = as new ‘globes; 7 graduations = time to change out ‘globes’.

Usually the ride will become harsh towards 7 graduations which indicates that 'globes' have lost much of their nitrogen pressure.

Also be aware that correct AHC pressures and correct AHC operation, “LO” > “N” > “HI”, tells you nothing about ‘globe’ condition.

Hope all goes well and that you enjoy the truck!!

If you have not seen the document elsewhere, recommend downloading the General Description of the AHC system from the following reference and suggest printing for easy referral (about 20 pages). It is an introductory descriptive document with diagrams and it is very helpful in gaining an understanding of how the Active Height Control (AHC) and the Toyota Electronic Modulated Suspension (TEMS) systems actually work:

https://lc100e.github.io/manual/
Look for the index tabs starting at top left hand side of the opening page and choose these tabs in order to reach the General Description document:
New Car Features > CHASSIS > Suspension > Active Height Control Suspension.

Other tabs in the index panel take you to more detail for diagnosis and repair.

The reference takes you to a genuine Toyota Factory Service Manual covering all Land Cruiser "100 series" models from 1998 to 2007. The main systems on the LX470 models are exactly the same as LC100 -- engines, transmissions, axles, suspensions including AHC, brakes, etc, etc -- so this reference suffices for most LX470 items. The LX470 does have some additional features and fittings and some different body details and these are not covered in this FSM version.

 

[LndXrsr]

Thought I’d post a personal experience update. Installed a set of King KTRS-79 springs on my truck today. I’ve slowly been loading up the LX with drawers, roof gear, armor, and knew I needed some more support from the springs to help the longevity of the AHC. Here are my results loaded with a trunk full of the heaviest stuff I could find in my garage as well as unloaded (which still includes a drawer system, tools/recovery gear, and a rooftop 3.5gal rotopax).

EDIT: I didn't disconnect the temp sensor for any of these measurements:

Loaded rear pressures (OEM —> King):
8.8 —> 7.4

Unloaded (OEM —> King)
8.1 —> 5.8

Pretty sure I had a good bit more weight in the loaded King test than the loaded OEM test so those numbers might be a bit pessimistic. Regardless, it puts me a lot closer to in spec. Front pressures stayed relatively unchanged in the high 6s to mid 7s range. Might crank the Tbars a bit more in the near future.

Oh, and the ride? It’s soooo much better. I aggressively took on some speed bumps today and it’s firm, controlled, not harsh at all, even unloaded. The difference between comfort and sport modes on the TEMS knob is much more noticeable too.

Definitely worth the investment for those running even just a little more weight on a daily basis than stock.

 

[Todd Atchison]

Suggest that your starting point is Techstream.

If you have not got Techstream or need help in setting it up the following thread provides excellent guidance:
How-To: TechStream In 5 Minutes - https://forum.ih8mud.com/threads/how-to-techstream-in-5-minutes.1034923/

The point is that you really need to know your AHC neutral pressures -- just make sure that there is adequate genuine fluid in the AHC tank, at least between the MAX/MIN lines, then measure AHC pressures after moving from "N" to "LO" then back to "N".

Various causes of your 'symptoms' are possible but a commonly this is indicative of 'globes' being at excessive pressure, due either to (1) huge loads in the vehicle, or more likely, (2) old age meaning tired front torsion bars and tired rear springs such that nowadays the AHC is carrying a greater share of the vehicle weight than it should. Either way, in this condition the system will refuse to lift to "HI" because pressures increase even further when the vehicle raises to "HI". The 'fix' at the front is easy and cheap -- turn both torsion bar adjusters equal turns clockwise (as seen when looking up at the bolt head) until front AHC pressures are in the specified range. After making this adjustment check and equalise front cross-level. The rear is a bit more complicated -- rear overpressure is not adjustable and usually requires correction at least by spacers, or better still, replacement rear springs. Suggest start at the front and go from there.

If your mechanic is new to AHC, explain that on an AHC vehicle, torsion bar adjustment is NOT used for adjusting the 'ride height' of the vehicle. (Height Control Sensor adjusters are used to adjust 'ride height').

If you have not seen them, also suggest having a look at the “Cheat Sheet”, video and explanation at this link:
Builds - The YotaMD Build - Cypress - https://forum.ih8mud.com/threads/the-yotamd-build-cypress.1184210/page-9#post-13383404

And also suggest go back to the begining “ABC’s of AHC” for a refresher:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520

Note that the 'graduation test' comes last when checking out AHC -- (1) cross-level, (2) get hub-to-fender distances right, (3) get AHC neutral pressures right, (4) check overall condition of 'globes' using 'graduation test' at correct AHC neutral pressures.

I ordered TechStream this weekend. The ODB2 / Blue Tooth Sensor works for reading and reseting codes but provides no other data.

 

[IndroCruise]

I ordered TechStream this weekend. The ODB2 / Blue Tooth Sensor works for reading and reseting codes but provides no other data.

As a shortcut, I use a “ELM327 Mini Interface” – widely available on Amazon and eBay for around USD11.00. I have found that this Interface works with the following App from Google Playstore on a Samsung Android tablet ….

ELMScan Toyota - Apps on Google Play - https://play.google.com/store/apps/details?id=com.obd2.elmscantoyota (Cost: around USD6.00 if I remember correctly).

…. even though my turbodiesel vehicle has the Toyota M-OBD system, not OBD2.

I have not been successful with other Apps. I am not sure whether this App also works with other ELM327 Interface devices.

The arrangement I use is pretty much plug-and-play although there is a bit of fiddling around to make it work because neither the Interface nor the App come with instructions. There are some useful videos on Youtube and some guidance also can be found here:

ELM327: 5 Best ELM327 Adapters/Interfaces 2021 [Review] - OBD Advisor - https://www.obdadvisor.com/elm327/

This is not as useful as the proper Techstream with cable to a relevant laptop as used by many IH8MUD Members – but it is low cost and Bluetooth connectivity to a tablet makes it easy to take the tablet around the car -- or attach it to the windscreen for testing/observation during real time driving.

I have found that the above arrangement is very useful for accessing the AHC Electronic Control Unit (ECU) for readings of AHC system – AHC pressures, Height Control Sensors, other Sensors, actions of various relays and solenoid valves and so on -- either in the garage at home or on the roadside.

Accessing the AHC ECU is my sole purpose with this arrangement -- I don’t use this arrangement on other ECU’s for other purposes.

 

[TNLCMama]

Hi Folks... first let me say, this thread is empowering. This fall I purchased, from older friends of mine, their 2003 LX470, with 125k miles on.
So my friends are late 60's and mid-80's. They offered the LX to me, letting me know they were going to junk it (were going to take $2.5k to junk it). This is a Maine vehicle but has been garage kept, so rust is minimal. It will remain in Maine and will be used in winter or to go to the mountains. It's my first Lexus but my 3rd 100 series, so I'm at least familiar with the vehicle. The 1st one, purchased new in 2000, was totaled by my then 17 yr old son at 230K miles after just putting in a remanned tranny (he walked away with a bruised thumb, which he got getting out the moon roof) and I am still driving my second one (a 2002 which I had modified and is now a "unicorn"). That truck is in Tennessee.

SO... thanks to y'all and my mechanic and his helper who knows these beasts, we have completely redone the AHC, the brakes, and a few other things. I do the purchasing (which has been fun, found some great leads with good prices, which I will share once this is done done done), and the guys do the wrenching.


We are coming down to the end and ... we need AHC fluid. I've found a place to buy it, I've read all the threads, and have come up with:
Toyota no longer produces 2.5L cans
I have seen for flush & bleed, everything from 2-3 2.5L cans, to 12 qts, to 3 qty 1L (a Paddo comment re: bleeding).

HOW MUCH FLUID DO I NEED for a completely NEW system??? It looks like the reservoir takes 4 liters... but I would presume one would need more than that to maintain pressure? (I'm getting in above my paygrade here). Should I purchase 12 L? 7 L? Help!!!

Thanks in advance~

 

[trdcorolla]

Hi Folks... first let me say, this thread is empowering. This fall I purchased, from older friends of mine, their 2003 LX470, with 125k miles on.
So my friends are late 60's and mid-80's. They offered the LX to me, letting me know they were going to junk it (were going to take $2.5k to junk it). This is a Maine vehicle but has been garage kept, so rust is minimal. It will remain in Maine and will be used in winter or to go to the mountains. It's my first Lexus but my 3rd 100 series, so I'm at least familiar with the vehicle. The 1st one, purchased new in 2000, was totaled by my then 17 yr old son at 230K miles after just putting in a remanned tranny (he walked away with a bruised thumb, which he got getting out the moon roof) and I am still driving my second one (a 2002 which I had modified and is now a "unicorn"). That truck is in Tennessee.

SO... thanks to y'all and my mechanic and his helper who knows these beasts, we have completely redone the AHC, the brakes, and a few other things. I do the purchasing (which has been fun, found some great leads with good prices, which I will share once this is done done done), and the guys do the wrenching.


We are coming down to the end and ... we need AHC fluid. I've found a place to buy it, I've read all the threads, and have come up with:
Toyota no longer produces 2.5L cans
I have seen for flush & bleed, everything from 2-3 2.5L cans, to 12 qts, to 3 qty 1L (a Paddo comment re: bleeding).

HOW MUCH FLUID DO I NEED for a completely NEW system??? It looks like the reservoir takes 4 liters... but I would presume one would need more than that to maintain pressure? (I'm getting in above my paygrade here). Should I purchase 12 L? 7 L? Help!!!

Thanks in advance~

When you say redone AHC, what was replaced exactly? What is new and what is old in your system? For reference I needed to run 2 metal cans through my AHC to get my my fluid coming out clean and a few plastic bottles later on when I replaced all my globes.

 

[tjb]

Just answered this privately, but the FSM says 3.7 liters of fluid is the system capacity.

When replacing the globes, I only got about 3-ish out - presumably the rest was in the shocks somewhere.

AHC Fluid

• tjb
• Mar 30, 2021
• ahc ahc fluid

FSM spec for AHC fluid

 

[TNLCMama]

When you say redone AHC, what was replaced exactly? What is new and what is old in your system? For reference I needed to run 2 metal cans through my AHC to get my my fluid coming out clean and a few plastic bottles later on when I replaced all my globes.

For the AHC,
New/replaced:
Front Shocks (RF, LF)
Rear Shocks (RR, LR)
Coil Springs (RR, LR)
AHC Air suspension Compressor Line/hose, front ds/ps, rear ds/ps (used but in excellent condition)
Front globes
Rear globes
Accumulators (RF, LF, RR, LR) & brackets
(Note: we got a complete set of used globes and accumulators that we have put in, but if the globes are bad, which we don't think they are as this vendor has provided excellent parts, we have a spare set of NEW globes).
Suspension Control Pump accumulator (used but in excellent condition)
Hydro suspension proportion valve/distrubution valve/Suspension control valve with bracket (used but in excellent condition)
variety of hoses

We have also replaced the PS gear assembly, L/R tie rods, PS pressure lines & return lines & pressure switch

Front pads, rotors, shims, clips, dust shields
Rear pads, rotors, shims, clips, etc
E-brake plates

Transmission cross member

fuel tank
Fuel pump

and purchased a full set of wheels with nearly new Michelin all-season tires (as the vehicle has heavy snow tires on right now). Again, used but in excellent condition

There may be a few other things...

Does that help???

Thanks,
Vivi

 

[TNLCMama]

Just answered this privately, but the FSM says 3.7 liters of fluid is the system capacity.

When replacing the globes, I only got about 3-ish out - presumably the rest was in the shocks somewhere.

AHC Fluid

• tjb
• Mar 30, 2021
• ahc ahc fluid

FSM spec for AHC fluid

Thanks!

 

[trdcorolla]

For the AHC,
New/replaced:
Front Shocks (RF, LF)
Rear Shocks (RR, LR)
Coil Springs (RR, LR)
AHC Air suspension Compressor Line/hose, front ds/ps, rear ds/ps (used but in excellent condition)
Front globes
Rear globes
Accumulators (RF, LF, RR, LR) & brackets
(Note: we got a complete set of used globes and accumulators that we have put in, but if the globes are bad, which we don't think they are as this vendor has provided excellent parts, we have a spare set of NEW globes).
Suspension Control Pump accumulator (used but in excellent condition)
Hydro suspension proportion valve/distrubution valve/Suspension control valve with bracket (used but in excellent condition)
variety of hoses

We have also replaced the PS gear assembly, L/R tie rods, PS pressure lines & return lines & pressure switch

Front pads, rotors, shims, clips, dust shields
Rear pads, rotors, shims, clips, etc
E-brake plates

Transmission cross member

fuel tank
Fuel pump

and purchased a full set of wheels with nearly new Michelin all-season tires (as the vehicle has heavy snow tires on right now). Again, used but in excellent condition

There may be a few other things...

Does that help???

Thanks,
Vivi

Wow, if you can get the fluid quickly, 8 might be enough assuming you don't have a lot of air in the system and expect to buy more if you do. If there is a lot of air, you'll go through a lot of fluid getting all of the air out.

 

[IndroCruise]

For the AHC,
New/replaced:
Front Shocks (RF, LF)
Rear Shocks (RR, LR)
Coil Springs (RR, LR)
AHC Air suspension Compressor Line/hose, front ds/ps, rear ds/ps (used but in excellent condition)
Front globes
Rear globes
Accumulators (RF, LF, RR, LR) & brackets
(Note: we got a complete set of used globes and accumulators that we have put in, but if the globes are bad, which we don't think they are as this vendor has provided excellent parts, we have a spare set of NEW globes).
Suspension Control Pump accumulator (used but in excellent condition)
Hydro suspension proportion valve/distrubution valve/Suspension control valve with bracket (used but in excellent condition)
variety of hoses

We have also replaced the PS gear assembly, L/R tie rods, PS pressure lines & return lines & pressure switch

Front pads, rotors, shims, clips, dust shields
Rear pads, rotors, shims, clips, etc
E-brake plates

Transmission cross member

fuel tank
Fuel pump

and purchased a full set of wheels with nearly new Michelin all-season tires (as the vehicle has heavy snow tires on right now). Again, used but in excellent condition

There may be a few other things...

Does that help???

Thanks,
Vivi

Thanks @TNLCMama, that information helps. Seems like a very thorough renovation of the AHC/TEMS system. Just to be clear on the details, here is a diagram with all the parts labelled in ‘Toyota/Lexus language’.

I suspect that “AHC Air suspension Compressor lines/hoses” in your post means the tubes/hoses from the AHC pump. There is no air and no air compressor in the AHC/TEMS system, just nitrogen behind the resin membranes in the Gas Chambers, also called ‘spheres’ or ‘globes’. “Suspension Control Pump accumulator” in your post probably means the long cylindrical Height Control Accumulator midway along the outside of Left Hand Side chassis rail, and, “hydro suspension proportion valve” probably means the Control Valve Assembly midway along the inside of Left Hand Side chassis rail.

It is unclear whether the AHC Pump and Motor assembly also has been replaced?

This illustration comes from https://lc100e.github.io/manual/ : go to tabs at Index Panel -- New Car Features (first item in the list) >CHASSIS > Suspension > Active Height Control Suspension & Skyhook TEMS. If not already seen, it is worthwhile to read this General Description of the AHC/TEMS system -- about 20 pages with many helpful diagrams, including diagrams of the hydraulic circuit at the last 4 pages.

Anyway, let’s get beyond the labels. This has been a huge project. Congratulations!

If the ‘Shock Absorbers’ have been replaced in dry condition, then it will take some effort to cause them to fill with AHC Fluid and purge the air remaining inside them. (The preferred method would have been to suck some fluid into the ‘Shock Absorbers’ before installation by operating them like a syringe to draw in some fluid from a container, so that they are partially filled with fluid and not completely full of air).

It is no problem if the ‘Shock Absorbers’ have been installed in dry condition, but the process will take a little longer because the ‘bleeding’ cycle and purging the air will need to be repeated several times. This will require more fluid. (Some IH8Mud Members suggest recycling AHC Fluid – this may be OK but there is a risk that air dissolved in the fluid remains in the system and also carries with it any debris picked up in the system. New fresh fluid is best – but obviously this is more expensive than recycling).

As shown by @tjb, the system capacity is around 3.7 litres but as mentioned by @trdcorolla, repeat ‘bleeds’ will require several times this amount of fluid, maybe at least 8 litres or more.

If I were doing your job, I would buy 4 x 2.5 litre drums of Toyota/Lexus Genuine AHC Fluid Part No. 08886-01805. These steel drums are available in my part of the world.

If these drums are not available in USA, then the alternative seems to be 1 litre plastic containers, Toyota/Lexus Genuine AHC Fluid Part No. 08886-81221.

(Supply in UK and maybe EU seems to be in 5 litre plastic drums, Toyota/Lexus Genuine AHC Fluid Part No. 08886-81260 -- not sure whether these are available in USA).

Whatever, it is important to use only Toyota/Lexus Genuine AHC Fluid in the AHC system. Using other fluids risks internal damage.

Given the magnitude of your project, may I also suggest that the three Height Control Sensors also are checked. These often are weak and problematic components on older LC100/LX470 vehicles fitted with AHC. They are covered in many IH8MUD threads.

More information on AHC Fluid:

AHC oil no longer available?

tried to buy some AHC oil today and the order was cancelled. when did Toyota and Lexus quit handling it? what are we supposed to replace it with???

forum.ih8mud.com

 

[TNLCMama]

Thanks @TNLCMama, that information helps. Seems like a very thorough renovation of the AHC/TEMS system. Just to be clear on the details, here is a diagram with all the parts labelled in ‘Toyota/Lexus language’.

I suspect that “AHC Air suspension Compressor lines/hoses” in your post means the tubes/hoses from the AHC pump. There is no air and no air compressor in the AHC/TEMS system, just nitrogen behind the resin membranes in the Gas Chambers, also called ‘spheres’ or ‘globes’. “Suspension Control Pump accumulator” in your post probably means the long cylindrical Height Control Accumulator midway along the outside of Left Hand Side chassis rail, and, “hydro suspension proportion valve” probably means the Control Valve Assembly midway along the inside of Left Hand Side chassis rail.

It is unclear whether the AHC Pump and Motor assembly also has been replaced?


View attachment 2631224


This illustration come from https://lc100e.github.io/manual/ : go to tabs at Index Panel -- New Car Features (first item in the list) >CHASSIS > Suspension > Active Height Control Suspension & Skyhook TEMS. If not already seen, it is worthwhile to read this General Description of the AHC/TEMS system -- about 20 pages with many helpful diagrams, including diagrams of the hydraulic circuit at the last 4 pages.

Anyway, let’s get beyond the labels. This has been a huge project. Congratulations!

If the ‘Shock Absorbers’ have been replaced in dry condition, then it will take some effort to cause them to fill with AHC Fluid and purge the air remaining inside them. (The preferred method would have been to suck some fluid into the ‘Shock Absorbers’ before installation by operating them like a syringe to draw in some fluid from a container, so that they are partially filled with fluid and not completely full of air).

It is no problem if the ‘Shock Absorbers’ have been installed in dry condition, but the process will take a little longer because the ‘bleeding’ cycle and purging the air will need to be repeated several times. This will require more fluid. (Some IH8Mud Members suggest recycling AHC Fluid – this may be OK but there is a risk that air dissolved in the fluid remains in the system and also carries with it any debris picked up in the system. New fresh fluid is best – but obviously this is more expensive than recycling).

As shown by @tjb, the system capacity is around 3.7 litres but as mentioned by @trdcorolla, repeat ‘bleeds’ will require several times this amount of fluid, maybe at least 8 litres or more.

If I were doing your job, I would buy 4 x 2.5 litre drums of Toyota/Lexus Genuine AHC Fluid Part No. 08886-01805. These steel drums are available in my part of the world.

If these drums are not available in USA, then the alternative seems to be 1 litre plastic containers, Toyota/Lexus Genuine AHC Fluid Part No. 08886-81221.

(Supply in UK and maybe EU seems to be in 5 litre plastic drums, Toyota/Lexus Genuine AHC Fluid Part No. 08886-81260 -- not sure whether these are available in USA).

Whatever, it is important to use only Toyota/Lexus Genuine AHC Fluid in the AHC system. Using other fluids risks internal damage.

Given the magnitude of your project, may I also suggest that the three Height Control Sensors also are checked. These often are weak and problematic components on older LC100/LX470 vehicles fitted with AHC. They are covered in many IH8MUD threads.

More information on AHC Fluid:

AHC oil no longer available?

tried to buy some AHC oil today and the order was cancelled. when did Toyota and Lexus quit handling it? what are we supposed to replace it with???

forum.ih8mud.com

IndroCruise, you are DA BOMB!!! First, thank you so much for that specific reference in the online manual. I have been to a bit of that manual (thanks to other threads here on MUD), although there gets to be a point where my eyes glaze over and I realize I'm looking at words but not understanding them. I've been lucky in that my mechanic and his helper (who is an old Mercedes and old Land Cruiser guy- and knows what an Australian Kelpie is as he has one and recognized mine!) have worked with me on this project. I had summarized about 30 pages of MUD notes I had taken, prior to bringing the Lexus to them, and had already made a spreadsheet of parts I believed I needed. They've helped me figure out what else I need, help me put together a list and then I go shopping. Again, these forums have been excellent tracking down parts, starting with part numbers, and even providing some recommendations when I look for parts in eBay. This has helped keep the cost down to manageable insanity.

To address your points:
The AHC Motor and pump have not been replaced. We believe they are in good working order.
The shocks were purchased from a dealership (wholesale prices) and shipped "wet" - and installed same.
Unfortunately, we in the US are unable to get the drums. I had already sourced the fluid, and found drums in the UK but alas not here. So 1 litre bottles it is. (My keyboard doesn't like that I spell litre the British way, sigh).
I have a source for the 1 litre bottles, xxx-812221, at really decent (comparatively speaking) prices. Just waiting to hear back from them as to why my VIN number doesn't work in their checkout. (Possibly because they're a Toyota dealership and mine is a Lexus). I will order enough for the bigger bleed. I'll also check to make sure there isn't some ridiculously short shelf life in case we don't use it all, this time.
I will most DEFINITELY check into the 3 height control sensors. Thanks for the tip.
I'm off to now do a LOT more reading. I TRULY appreciate all your help.

 

[IndroCruise]

IndroCruise, you are DA BOMB!!! First, thank you so much for that specific reference in the online manual. I have been to a bit of that manual (thanks to other threads here on MUD), although there gets to be a point where my eyes glaze over and I realize I'm looking at words but not understanding them. I've been lucky in that my mechanic and his helper (who is an old Mercedes and old Land Cruiser guy- and knows what an Australian Kelpie is as he has one and recognized mine!) have worked with me on this project. I had summarized about 30 pages of MUD notes I had taken, prior to bringing the Lexus to them, and had already made a spreadsheet of parts I believed I needed. They've helped me figure out what else I need, help me put together a list and then I go shopping. Again, these forums have been excellent tracking down parts, starting with part numbers, and even providing some recommendations when I look for parts in eBay. This has helped keep the cost down to manageable insanity.

To address your points:
The AHC Motor and pump have not been replaced. We believe they are in good working order.
The shocks were purchased from a dealership (wholesale prices) and shipped "wet" - and installed same.
Unfortunately, we in the US are unable to get the drums. I had already sourced the fluid, and found drums in the UK but alas not here. So 1 litre bottles it is. (My keyboard doesn't like that I spell litre the British way, sigh).
I have a source for the 1 litre bottles, xxx-812221, at really decent (comparatively speaking) prices. Just waiting to hear back from them as to why my VIN number doesn't work in their checkout. (Possibly because they're a Toyota dealership and mine is a Lexus). I will order enough for the bigger bleed. I'll also check to make sure there isn't some ridiculously short shelf life in case we don't use it all, this time.
I will most DEFINITELY check into the 3 height control sensors. Thanks for the tip.
I'm off to now do a LOT more reading. I TRULY appreciate all your help.

Just a suggestion -- but it does involve a bit more reading ....

Given the effort that is going into your truck, it may be worthwhile for peace of mind to physically check the AHC Pump even without replacing it. This is an unusual but not difficult job, best done at a time when major bleeding of the AHC system must happen anyway for other purposes.

The aim is to dis-assemble the AHC Pump and clean by backflushing the tiny strainers inside the pump. It is not necessary to pull out the strainers.

The pump is a small-volume, high-pressure gear pump -- "small" means each of the two gears are smaller in diameter than a US dime and not much thicker than two (maybe three) US dimes held together. The pump is reliable and longlife, but intolerant of even small particles of junk passing through it. The strainers provide important protection of the pump, but over a long period of time, or if somehow the wrong fluid or other impurities have entered the system, then the strainers themselves may partially block, causing reduced delivery of pressure and flow, and consequent poor performance of the AHC/TEMS system.

Some explanations with pictures concerning the AHC Pump can be found at these links:

Post #67 by @BullElk at AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/page-4#post-13401098 for pictures of a pump partially clogged with old AHC Fluid which has turned into a jelly.

Posts #69 and #70 by @IndroCruise at AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/page-4#post-13407297 and onwards shows pictures of AHC Pump disassembly and also show the tiny filters (strainers) within the Pump.

Pump disassembly, cleanup of the pump and backwashing the filters (strainers) are all straightforward and is made easy by removing the motor/pump/tank assembly from the vehicle.

It is also a good time to electrically check the Pressure Sensor and the Temperature Sensor at the Pump -- needs a 4.5volt source (three AA cells in series) and a decent multimeter. This is a simple test, details can be found in the AHC "DIAGNOSTICS" section of the "Repair Manual" part of the FSM.

I wrote some other notes for another IH8MUD Member over the last few weeks. His problems are different but some of the explanations about the AHC/TEMS system may be of interest.

Ahc problems. - https://forum.ih8mud.com/threads/ahc-problems.1242268/#post-13666261

 

[TNLCMama]

Just a suggestion -- but it does involve a bit more reading ....

Given the effort that is going into your truck, it may be worthwhile for peace of mind to physically check the AHC Pump even without replacing it. This is an unusual but not difficult job, best done at a time when major bleeding of the AHC system must happen anyway for other purposes.

The aim is to dis-assemble the AHC Pump and clean by backflushing the tiny strainers inside the pump. It is not necessary to pull out the strainers.

The pump is a small-volume, high-pressure gear pump -- "small" means each of the two gears are smaller in diameter than a US dime and not much thicker than two (maybe three) US dimes held together. The pump is reliable and longlife, but intolerant of even small particles of junk passing through it. The strainers provide important protection of the pump, but over a long period of time, or if somehow the wrong fluid or other impurities have entered the system, then the strainers themselves may partially block, causing reduced delivery of pressure and flow, and consequent poor performance of the AHC/TEMS system.

Some explanations with pictures concerning the AHC Pump can be found at these links:

Post #67 by @BullElk at AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/page-4#post-13401098 for pictures of a pump partially clogged with old AHC Fluid which has turned into a jelly.

Posts #69 and #70 by @IndroCruise at AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/page-4#post-13407297 and onwards shows pictures of AHC Pump disassembly and also show the tiny filters (strainers) within the Pump.

Pump disassembly, cleanup of the pump and backwashing the filters (strainers) are all straightforward and is made easy by removing the motor/pump/tank assembly from the vehicle.

It is also a good time to electrically check the Pressure Sensor and the Temperature Sensor at the Pump -- needs a 4.5volt source (three AA cells in series) and a decent multimeter. This is a simple test, details can be found in the AHC "DIAGNOSTICS" section of the "Repair Manual" part of the FSM.

I wrote some other notes for another IH8MUD Member over the last few weeks. His problems are different but some of the explanations about the AHC/TEMS system may be of interest.

Ahc problems. - https://forum.ih8mud.com/threads/ahc-problems.1242268/#post-13666261

I am so VERY grateful. I'm meeting with Paul later this morning to go over punch lists and I have printed immediate relevant parts (he doesn't like to read on computers, so I do that part too), and will bring my iPad to go over the info in the manual- both from your suggestion above, and from that last thread's information on diagnostics and codes.

YOU are a wealth of information and I am thoroughly appreciative to receive it.

One last quick question. I have a list of suppliers who've been good to work with and with decent prices. I tried to go with new where I could afford it... just because. But have also found a purveyor in used parts (he does all sorts of vehicles), along with the two dealerships who are selling online at wholesale prices (one with a free shipping coupon up to $75... believe me it saves a ton of $). Where should I post that information? Here or in The Definite List of AHC Maintenance Items... or both? Thanks so very much! Hope to have my Lexus in the next week or so. Fingers crossed (and armed with your knowledge).

 

[IndroCruise]

One last quick question. I have a list of suppliers who've been good to work with and with decent prices. I tried to go with new where I could afford it... just because. But have also found a purveyor in used parts (he does all sorts of vehicles), along with the two dealerships who are selling online at wholesale prices (one with a free shipping coupon up to $75... believe me it saves a ton of $). Where should I post that information? Here or in The Definite List of AHC Maintenance Items... or both? Thanks so very much! Hope to have my Lexus in the next week or so. Fingers crossed (and armed with your knowledge).

This thread has a large number of people who watch it and it is newer thread than the very long "Definitive ...." thread. It is your choice -- maybe starting a new thread using an attention-grabbing title referring to parts supply is the way to go ....

 

[js47]

HELP!! I was flushing my AHC today and snapped off the accumulator bleeder.... Will post photos below. No fluid has left the accumulator but I am still in L mode. I wonder if the partial bleeder can handle the pressure?

The system is otherwise in great condition –– globes and shocks replaced by PO at Lexus <40k miles ago, 14+ graduations before the flush. I was not expecting anything to break considering the young age of the system, but I guess the accumulator must be original. Any suggestions for what I should do?

TIA

 

[tjb]

HELP!! I was flushing my AHC today and snapped off the accumulator bleeder.... Will post photos below. No fluid has left the accumulator but I am still in L mode. I wonder if the partial bleeder can handle the pressure?

The system is otherwise in great condition –– globes and shocks replaced by PO at Lexus <40k miles ago, 14+ graduations before the flush. I was not expecting anything to break considering the young age of the system, but I guess the accumulator must be original. Any suggestions for what I should do?

TIA


View attachment 2639527
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Those guys are a couple of bucks each if you can get what’s left of it cleanly out. I have a handful of them on hand for such an event, but have never had to use one. Part No 49189-60010

49189-60010 Genuine Lexus Plug, BLEEDER Suspension

Genuine 49189-60010 Plug, BLEEDER Suspension fits 1998-2021 Lexus LX470, LX570. LexusPartsNow offers 4918960010 for $2.58.

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