AHC Non-Function and Fluid Low (1 Viewer)

Joined
Feb 12, 2020
Messages
24
Location
St. Louis
Hi, thanks for the forum. I just picked up a rust free 2005 LX470 with 192k miles. Unfortunately there will be some work done to get it baselined. I did not have a chance to personal inspect it before purchase and was under the impression the AHC was good. But today I found out the AHC does not function as it should and then realized the fluid is very low. I did searched the forum and was not able to find someone have exact same situation.

Here is a rundown of the actions and how I found the issue. I change to AHC to Hi with parking break up and close the door, me outside the truck. The truck went up, then I began to hear some squealing noise coming from the under of the truck, not sure exactly where the sound come from (the sound is a little like the sound of an oil serpentine belt, but it is lower). Then the sound was gone, and the truck began to come down automatically from high. Then I see the AHC Off light begin to blink and the AHC light changed from H to N. I opened the door and changed the AHC to LO, closed the door and me outside the truck. The car would not go down and the OFF light keep blinking. I tried to click the AHC off button, and it did not work. Then I checked the AHC fluid. The fluid is at about 4th - 5th lines from the bottom of reserver (the truck is at N height). I removed the cap and the filter, the color of the fluid is brown. Per the previous history, I don't see a record that the AHC was serviced in it's life.

Here is my thought process on next steps.
1. Fill the reserver with AHC fluid to Max
2. Test the AHC again to see if the Off light is still blinking or if this fix the issue.
3. Examine if any leaks in the AHC system if it still not fix the issue.

I believe I would need to get the AHC functional first, then I can see the difference of the fluid level from H to L to determine how well the function is. Then I can go from there to see what the next step will be with existing posts from here.

Any suggestions on the testing or I should do it another way, I would highly appreciate it.

Some pics of the truck undercarriage.
IMG_5552.JPG


IMG_5551.JPG

IMG_5553.JPG
IMG_5550.JPG

Here is a pic of the AHC reserver.
Screen Shot 2021-01-09 at 10.18.29 PM.png
 
Joined
Dec 6, 2016
Messages
250
Location
Brisbane, Australia
Hi, thanks for the forum. I just picked up a rust free 2005 LX470 with 192k miles. Unfortunately there will be some work done to get it baselined. I did not have a chance to personal inspect it before purchase and was under the impression the AHC was good. But today I found out the AHC does not function as it should and then realized the fluid is very low. I did searched the forum and was not able to find someone have exact same situation.

Here is a rundown of the actions and how I found the issue. I change to AHC to Hi with parking break up and close the door, me outside the truck. The truck went up, then I began to hear some squealing noise coming from the under of the truck, not sure exactly where the sound come from (the sound is a little like the sound of an oil serpentine belt, but it is lower). Then the sound was gone, and the truck began to come down automatically from high. Then I see the AHC Off light begin to blink and the AHC light changed from H to N. I opened the door and changed the AHC to LO, closed the door and me outside the truck. The car would not go down and the OFF light keep blinking. I tried to click the AHC off button, and it did not work. Then I checked the AHC fluid. The fluid is at about 4th - 5th lines from the bottom of reserver (the truck is at N height). I removed the cap and the filter, the color of the fluid is brown. Per the previous history, I don't see a record that the AHC was serviced in it's life.

Here is my thought process on next steps.
1. Fill the reserver with AHC fluid to Max
2. Test the AHC again to see if the Off light is still blinking or if this fix the issue.
3. Examine if any leaks in the AHC system if it still not fix the issue.

I believe I would need to get the AHC functional first, then I can see the difference of the fluid level from H to L to determine how well the function is. Then I can go from there to see what the next step will be with existing posts from here.

Any suggestions on the testing or I should do it another way, I would highly appreciate it.

Some pics of the truck undercarriage.View attachment 2548996

View attachment 2548991
View attachment 2548999View attachment 2549000
Here is a pic of the AHC reserver.
View attachment 2549008

Strongly agree with @ramangain.

Suggest as follows:

Read this:

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/

And watch this video:

AHC Basics for dummies Video re CrossLeveling, Height Sensor adjustment, TB tweaking | IH8MUD Forum

And read this:

Low AHC Fluid Question - https://forum.ih8mud.com/threads/low-ahc-fluid-question.1228147/#post-13416367

And be aware that this Landcruiser Factory Service Manual (FSM) source also applies to AHC/TEMS on LX470.

https://lc100e.github.io/manual/

Start by having a good read of the General Description of the AHC and TEMS systems – follow these drop-down tabs on the index page:

New Car Features > CHASSIS > Suspension > Active Height Control Suspension and Skyhook TEMS

There are about 20 pages with many diagrams which give a good idea of how the AHC and TEMS systems work. Do not worry that it seems to apply to an older model – this section also applies to your model as well. This document is a ‘must read’ as it will be hard to make sense of the comments below or in other threads without looking at the explanations and diagrams in this document.

First impressions and a few thought-starters looking at your symptoms:

  • Truck looks good underneath and area around AHC Pump and its motor look clean – nevertheless, have a very good look for leaks in the AHC system.
AHC Leakage Check.jpg

  • If no leaks, where did the fluid go? At this age and mileage, it is likely that the ‘globes’ (called Gas Chambers in the FSM) have failed. This means that the nitrogen behind the membrane has leaked out and the ‘globes’ are now full of fluid. With a failed membrane and without nitrogen pressure behind the membrane to push the fluid back to the AHC Tank, the fluid in the ‘globe’ stays where it is. Testing the number of graduations at the AHC tank between “HI” and “LO” height settings is important to understand the overall condition of ‘globes’ – but this cannot be done until the system is working again,

  • The AHC Fluid level at the AHC Tank in the picture is very low – so low that air may have been sucked into the system. If so, the AHC Pump would be noisy for a short time before it switched itself “OFF” and the “OFF” light would show in the instrument panel.

  • At this age and mileage, it is also likely that the front torsion bars and especially the rear springs are ‘tired’ and have lost some of their strength. If so, the AHC system will be carrying an excessive share of the vehicle weight. Consequently, the AHC pressures will be too high. It is also very possible that they are so high that the AHC pressure limits are being exceeded – which would mean that the vehicle may refuse to raise to “HI” – and may even drop to “LO” and stay there.

There may be other deeper problems not yet identified – but it is important to fix these basic problems first.

So what to do?

Exactly as @ramangain mentioned already as a starter:

  1. Dump some fluid into the AHC Tank (be careful to use only genuine Toyota/Lexus AHC Fluid), optimally up to the reservoir clamshell seam (above H mark). Later, as part of fixing these problems, it will be necessary to bleed the whole system WITHOUT drawing in air – so start with a higher level of fluid,
  2. Get a 30mm socket – necessary to turn torsion bar adjusters to get more weight onto the torsion bars and off the AHC system, thereby lowering the AHC pressures,
  3. Get Techstream or equivalent to read AHC pressure – start with this advice: How-To: TechStream In 5 Minutes - https://forum.ih8mud.com/threads/how-to-techstream-in-5-minutes.1034923/
  4. Follow the guidance given in the first two threads mentioned above.
 
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Joined
Jun 19, 2013
Messages
2,359
Location
Mobile, AL
I think your fluid is just low. Add AHC fluid and see if everything works as normal. If not, the pump may have gelled up and not pumping fluid. Check for any bad leaks particularly at the top of "shocks".
 
Joined
Dec 6, 2016
Messages
250
Location
Brisbane, Australia
Thanks for everyone's reply. @IndroCruise I appreciate the detail list on readings and possible causes for the issue. I think I know what to do next.
No problem @UltTrail runner -- many people on this forum have helped me in past, so I try to make some contribution as well. @BullElk provides a good reminder about AHC Pump issues and you will see some relevant discussion at the recent Post #231 at the thread below --which leads to other posts and pictures. Hopefully your situation is resolved before any of that becomes necessary!

 

suprarx7nut

The YotaMD Guy
Supporting Vendor
Joined
Sep 28, 2010
Messages
3,761
Location
Colorado
I bet that sqeauling noise was the AHC pump trying to pump, but without fluid in the reservoir. Top off fluid and try again.

Get Techstream or another tool that can read that data. AHC diagnostics without that data is a guessing game.
 
Joined
Feb 12, 2020
Messages
24
Location
St. Louis
Update: I got Toyota AHC fluid (Part# 08886-81221). Filled the reservoir to almost clamshell seam. Tested the AHC from Hi to Lo 3 times. Measured the fluid level difference in the reservoir 3 times. The H and L fluid level for each test is basically the same. As the fluid is higher than the clamshell when the truck is in Low so I can only measure the distance between the 2 marks. It is about 3.5cm to 4cm, which is about 12 notches if I transfer the measurement to the lower reservoir marks. Based on what I am reading here. I would assume the system is in good working order as this is >9. I did buy extra AHC fluid for a bleed job, but I may not tackle it right now. So am I good to just leave the fluid in the AHC reservoir like this above the Max mark?

1st picture shows the fluid level after I added AHC fluid.
2nd picture shows the fluid level when the truck set on Hi
3rd picture shows the fluid level when the truck set on Lo

Thanks again for all the help.
Screen Shot 2021-01-15 at 5.34.32 PM.png
Screen Shot 2021-01-15 at 5.34.50 PM.png
Screen Shot 2021-01-15 at 5.35.00 PM.png
 
Joined
Aug 17, 2020
Messages
546
Location
likely in the salvage yard
Yes the extra fluid is fine to leave in. As far as the flush you might as well wait to flush and adjust TB's until after you have Techstream to monitor the pressures. In the mean time just keep an eye on the reservoir level in N. Your engine compartment is immaculate by the way that must be a beautiful truck.
 
Joined
Dec 6, 2016
Messages
250
Location
Brisbane, Australia
Update: I got Toyota AHC fluid (Part# 08886-81221). Filled the reservoir to almost clamshell seam. Tested the AHC from Hi to Lo 3 times. Measured the fluid level difference in the reservoir 3 times. The H and L fluid level for each test is basically the same. As the fluid is higher than the clamshell when the truck is in Low so I can only measure the distance between the 2 marks. It is about 3.5cm to 4cm, which is about 12 notches if I transfer the measurement to the lower reservoir marks. Based on what I am reading here. I would assume the system is in good working order as this is >9. I did buy extra AHC fluid for a bleed job, but I may not tackle it right now. So am I good to just leave the fluid in the AHC reservoir like this above the Max mark?

1st picture shows the fluid level after I added AHC fluid.
2nd picture shows the fluid level when the truck set on Hi
3rd picture shows the fluid level when the truck set on Lo

Thanks again for all the help.
View attachment 2554368View attachment 2554369View attachment 2554370
Agree with @LXKevin. The colour of the AHC fluid looks good – and so does the engine bay and underbody! The high level of fluid only becomes a problem if the vehicle is on such an extreme slope that spillage might occur. It is very unlikely that you would be on an extreme slope with the vehicle set at “LO” height which is when the level in the tank is highest. It does make it a little more difficult to determine how many graduations between height at “LO”and height at “HI” but you have figured out how to extrapolate – so no problem. You can always pull some fluid out with a turkey baster or similar if you wish.

As you know, when (1) the vehicle is at correct hub-to-fender heights, and (2) AHC neutral pressures are within the specified range (preferably mid-range or maybe a little lower), then 14 graduations = ‘globes’ in as-new condition; 8 graduations = order new ‘globes’ and get ready to change; 7 graduations = change ‘globes’ now for continuing good damping performance.

So 9 graduations is fine for now – suggest re-test each 6 months to see whether there is any change.

To summarise, the point is that you want
  • the front of the vehicle to be correctly cross-levelled as measured hub-to-fender with a tape – adjust and equalise front ‘static heights’ as necessary by equal and opposite turns with torsion bar adjusters per FSM with engine “OFF”,
  • then, check ‘operating heights’ as recommended by IH8MUD as measured hub-to-fender with a tape, front 19.75 inches and rear 20.50 inches (adjust ‘operating heights’ with Height Control Sensor adjusters not torsion bar adjusters, measure with engine “ON” but for safety turn “OFF” engine while doing actual adjustments),
  • then when heights are correct (important because heights affect pressures), measure front and rear AHC pressures with Techstream, check within FSM-specified range, adjust front AHC pressures by equal torsion bar adjuster turns in same direction to transfer weight to torsion bars and reduce AHC pressure (or vice versa), correct rear AHC pressures if necessary with spacers or new springs,
  • finally, check HI/LO graduations at AHC tank as the last step to obtain readings under correct conditions and which can be compared with the FSM and give an idea of overall ‘globe’ condition (but not individual 'globe' condition). Note: AHC pressures tell nothing about ‘globe’ condition. The idea of this test under correct pressure conditions is to watch the slow but inevitable deterioration of ‘globes’ over time (loss of nitrogen gas, eventually gas space behind membrane steadily fills with fluid, membrane pushes less and less fluid back to the AHC Tank as ‘globes’ get older, meaning they ‘wear out’, and less and less graduations are seen at the tank – until ‘globe’ replacement is required.).
Seems like a you have a very good truck! Basic preventative maintenance (including AHC/TEMS) will keep it going for a very long time. Hope all goes well!
 
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