Definitive list of AHC maintenance items (5 Viewers)

[Azi]

Bought a 100 last week, so pretty much new to everything.
I went through most of the pages in the thread and did quite a lot of search over the web, but still no solution to my problem.

I am located in EU and the car is EU Toyota Land Cruiser 100 '00 equipped with AHC.
It is going up and down (Hi Lo) flawlessly and fast and the comfort switch works with a very noticeable difference.
BUT...
The car rides very bumpy and bouncy. It is near impossible to drive/unstable in the city, on a highway is fine.
For example, city speed bumps, when I pass them feels like a boat going up and down, up and down...like the old rap videos.

I went to the local dealer and directly flushed the AHC oil. It is literally new (2 days) but the situation didn't get any better at all.
The difference in the reservoir from Lo to Hi are 3 graduations (marks) It was the same before the flush...

Also, I am observing a significant difference in the height of the vehicle (cap to fender), compared to the ones quoted here for LX470.
FSM says 19,75" front and 20,5" rear .... What I have is 28,5" front and 30" rear. Well, I am running bigger tires, but still, that is center cap fender - shouldn't reflect?! Maybe that's another difference from LX470 to LC100...

I just ordered diagnostic cable and software, so I will work with them during the weekend and post my pressures.

I would be very glad if someone points me toward something because here, in Bulgaria, we have no mechanics for such cars and I have literally no one to help me.

Thank you in advance!

Cheers,
Azi

 

[Uwiik]

Hi all,
What should I suspect when it takes 30-40 seconds to raise from L to N? It also couldn’t raise itself to H (two blinks then nothing).

 

[menancyandsam]

Bought a 100 last week, so pretty much new to everything.
I went through most of the pages in the thread and did quite a lot of search over the web, but still no solution to my problem.

I am located in EU and the car is EU Toyota Land Cruiser 100 '00 equipped with AHC.
It is going up and down (Hi Lo) flawlessly and fast and the comfort switch works with a very noticeable difference.
BUT...
The car rides very bumpy and bouncy. It is near impossible to drive/unstable in the city, on a highway is fine.
For example, city speed bumps, when I pass them feels like a boat going up and down, up and down...like the old rap videos.

I went to the local dealer and directly flushed the AHC oil. It is literally new (2 days) but the situation didn't get any better at all.
The difference in the reservoir from Lo to Hi are 3 graduations (marks) It was the same before the flush...

Also, I am observing a significant difference in the height of the vehicle (cap to fender), compared to the ones quoted here for LX470.
FSM says 19,75" front and 20,5" rear .... What I have is 28,5" front and 30" rear. Well, I am running bigger tires, but still, that is center cap fender - shouldn't reflect?! Maybe that's another difference from LX470 to LC100...

I just ordered diagnostic cable and software, so I will work with them during the weekend and post my pressures.

I would be very glad if someone points me toward something because here, in Bulgaria, we have no mechanics for such cars and I have literally no one to help me.

Thank you in advance!

Cheers,
Azi

I don't think it's possible to go that high. You must be measuring wrong (center of cap to the fender). My understanding is that the AHC sensor adjusted rigs have a max. increase of 2.5" over factory. Otherwise you get into dangerous geometry issues.

Re-check heights & check your pressures & report back.

 

[Moridinbg]

3 graduations usually means that the pressurised globes are way too worn. Below 7 they are not good and brand new they do 14 graduations.
What are your pressures?

Hi all,
What should I suspect when it takes 30-40 seconds to raise from L to N? It also couldn’t raise itself to H (two blinks then nothing).

What is more important than time is how many graduations do you have between L & H and what are your pressures as well

 

[Azi]

Hi @Moridinbg

Happy to see you around!
I already met you in another forum - offroad-bulgaria. I am the Barbarian

I am attaching a screenshot of my live data from TechStream:

The attached screenshot is on a flat level surface, with only me in the car and almost empty tank.

Today, I will perform another test with a full tank and will keep you posted.

What bothers me the most is the difference in the height control sensors:
FR: 4.4mm
FL: -9.0mm
RR: 0.6mm

I guess I have to play around with the height sensors?
If so, what are the perfect measures I must chase? Three zeros?

However, I also performed a double-check with the tape and it indeed proved the difference.
I will attach later the exact data from the tape.

Cheers,
Azi


UPDATE:

Just performed another test will full tank - attaching the results:

The height control sensors now are even weirder.
FR: 7,4mm
FL: -12,4mm
R: 1,4mm

Also, I re-measured the center cap to fender distance and it looks good.
My first measures were wrong - bottom of the rim to fender, not center cap to fender.

Attaching the results of the measurements:

Converted to inches and having in mind the manufacturer's numbers - Front 19,75" / Rear 20,5" it looks OK.
There is a slight 1cm difference from left and right (0,39" - less than a half-inch) in both rear and front, but still almost at the right height:
Front: 19,48"
Rear: 19,88"

Also, I took a few photos of both front height control sensors and they look OK, not damaged/twisted.
Attaching the photos:

Front left (Driver's side):

and front right (passenger's side)

Any guidance would be appreciated in order to solve the bouncy ride...

Cheers,
Azi

 

[Cetus]

Hi @Moridinbg

Happy to see you around!
I already met you in another forum - offroad-bulgaria. I am the Barbarian

I am attaching a screenshot of my live data from TechStream:

View attachment 2211431

The attached screenshot is on a flat level surface, with only me in the car and almost empty tank.

Today, I will perform another test with a full tank and will keep you posted.

What bothers me the most is the difference in the height control sensors:
FR: 4.4mm
FL: -9.0mm
RR: 0.6mm

I guess I have to play around with the height sensors?
If so, what are the perfect measures I must chase? Three zeros?

However, I also performed a double-check with the tape and it indeed proved the difference.
I will attach later the exact data from the tape.

Cheers,
Azi


UPDATE:

Just performed another test will full tank - attaching the results:
View attachment 2211426

The height control sensors now are even weirder.
FR: 7,4mm
FL: -12,4mm
R: 1,4mm

Also, I re-measured the center cap to fender distance and it looks good.
My first measures were wrong - bottom of the rim to fender, not center cap to fender.

Attaching the results of the measurements:
View attachment 2211428

Converted to inches and having in mind the manufacturer's numbers - Front 19,75" / Rear 20,5" it looks OK.
There is a slight 1cm difference from left and right (0,39" - less than a half-inch) in both rear and front, but still almost at the right height:
Front: 19,48"
Rear: 19,88"

Also, I took a few photos of both front height control sensors and they look OK, not damaged/twisted.
Attaching the photos:

Front left (Driver's side):
View attachment 2211429

and front right (passenger's side)

View attachment 2211430

Any guidance would be appreciated in order to solve the bouncy ride...

Cheers,
Azi

I had the same issues. The ride was bouncy and harsh. I replace all 4 globes and the ride is awesome again. I had about 6-7 graduations from low to high. Now I'm at about 14 graduations.

 

[Uwiik]

3 graduations usually means that the pressurised globes are way too worn. Below 7 they are not good and brand new they do 14 graduations.
What are your pressures?



What is more important than time is how many graduations do you have between L & H and what are your pressures as well

my accumulator pressure is between 10.3 - 10.5 MPA consistently. Previously I made a mistake of not paying any attention to equalizing height sensors reading after setting cross level and F-R pressures, I rectified that mistake last week and the small tweak to equalize height sensors reading transformed the comfort level substantially. As it is right now, I have Front Press at 6.9 MPA, Rear Press at 5.4 MPA, Accumulator Press 10.3-10.5 MPA, Front hub to arch 50mm/19.7”, Rear hub to arch 52mm/20.5”, almost flat out 0 sensors reading with minor +/- 2mm deltas between all three sensors (FR-FL-RR)

I couldn’t tell on the graduation mark between L to H because my truck wouldn’t go to H and I am still trying to figure out why? I do have steering angle sensor DTC (C1777), but I doubt that is the culprit for my truck won’t raise to H? I suspect worn pump or accumulator cylindrical tube due to how long it takes between L to N which in my case always between 30-45 seconds where it supposed to be around 15 seconds? Weak something???

I highly doubt that my problem have anything to do with the condition of my globes. As @PADDO pointed out a few times on this thread, even with worn globes all AHC parameters (press, sensors, etc) shouldn’t get affected and all AHC function should function as normal, only with bouncy/harsh ride if the globes are shot. On top of that, my truck is currently riding extremely comfortable, my friends who regularly sat on the truck are all commenting how smooth the ride is. It absorbs most potholes and un even road well, couldn’t even feel small road crack on the road, so I know that my globes are good, even the previous owner claimed he replaced all 4 globes last year. As far as I know the first sign of worn globes is that you can feel small road crack and things get bouncy, and I definitely do not have these problem.

I don’t have handling or comfort issue at all with my truck, it’s just that it won’t raise to H and it takes 30-45 seconds to raise from L no N.

Advices please and thanks a lot!!

 

[Azi]

Tagging @PADDO & @uHu, the AHC gurus as last hope.

 

[uHu]

Tagging @PADDO & @uHu, the AHC gurus as last hope.

Get your values within specs first. It's all explained in this and other threads here. It doesn't get fixed by itself. I.e. adjust torsion bars, adjust sensors, change coils, redo readings, etc.

@Uwiik - If steering signal doesn't indicate somewhere close to center, the AHC will not rise to Hi.

 

[Moridinbg]

Hi @Moridinbg

Happy to see you around!
I already met you in another forum - offroad-bulgaria. I am the Barbarian

Any guidance would be appreciated in order to solve the bouncy ride...

Cheers,
Azi

Start here - #433 - this 8 quotes (mostly repeating themselves) from PADDO are the gist of adjusting the AHC system. Really simple stuff.

1 full clockwise turn of the torsion bar adjuster will rise that corner 1/8". Counter clockwise turns drop it. Get FL & FR at the same level - that would be 3 CCW turns on the right torsion bar.
Once they are level, start dropping the pressure - again adjusting the torsion bars, but this time both of them the same amount. 1 CW turn drops 0.2MPa.
This should also sort the sensor difference out. If not, you can adjust that too.

After this is done you can measure graduations. Before that it's meaningless.

 

[IndroCruise]

Hi @Moridinbg

Happy to see you around!
I already met you in another forum - offroad-bulgaria. I am the Barbarian

I am attaching a screenshot of my live data from TechStream:

View attachment 2211431

The attached screenshot is on a flat level surface, with only me in the car and almost empty tank.

Today, I will perform another test with a full tank and will keep you posted.

What bothers me the most is the difference in the height control sensors:
FR: 4.4mm
FL: -9.0mm
RR: 0.6mm

I guess I have to play around with the height sensors?
If so, what are the perfect measures I must chase? Three zeros?

However, I also performed a double-check with the tape and it indeed proved the difference.
I will attach later the exact data from the tape.

Cheers,
Azi


UPDATE:

Just performed another test will full tank - attaching the results:
View attachment 2211426

The height control sensors now are even weirder.
FR: 7,4mm
FL: -12,4mm
R: 1,4mm

Also, I re-measured the center cap to fender distance and it looks good.
My first measures were wrong - bottom of the rim to fender, not center cap to fender.

Attaching the results of the measurements:
View attachment 2211428

Converted to inches and having in mind the manufacturer's numbers - Front 19,75" / Rear 20,5" it looks OK.
There is a slight 1cm difference from left and right (0,39" - less than a half-inch) in both rear and front, but still almost at the right height:
Front: 19,48"
Rear: 19,88"

Also, I took a few photos of both front height control sensors and they look OK, not damaged/twisted.
Attaching the photos:

Front left (Driver's side):
View attachment 2211429

and front right (passenger's side)

View attachment 2211430

Any guidance would be appreciated in order to solve the bouncy ride...

Cheers,
Azi

Hi Azi,

Welcome from another student in this very useful “AHC Academy”!! I started only a short period of time before you and I sense your frustration. We have all been there!

You mentioned at post #701 in this string that

“I went to the local dealer and directly flushed the AHC oil. It is literally new (2 days) but the situation didn't get any better at all. The difference in the reservoir from Lo to Hi are 3 graduations (marks). It was the same before the flush ....

Sadly, few dealerships seem to contain much expertise or skill in dealing with AHC matters so we rely heavily on IH8MUD and self-diagnosis ….

Afterwards at post #705 you described great progress with measuring correct heights from wheelhub centre to fender. By the way and just to be clear, the recommendations of 19.5” (Front) and 20.5” (Rear) are not manufacturer’ recommendations but good practical approximations provided by IH8MUD Members. These numbers have been derived from the more detailed (and more difficult) measurements depicted in Factory Service Manual (FSM) – see attachments. These approximations are fit-for-purpose and are widely used.

You also connected successfully with Techstream and obtained some measurements depicted in the same post #705. Congratulations on this speedy progress! Some of us have taken months to get Techstream or other alternatives to work properly.

Probably you know all this but just to be sure, it is very important when measuring pressures to do this just after raising the vehicle from “LO” to “N” and after say 30 to 60 seconds with the engine running to ensure that the AHC pump has finished re-charging the height control accumulator, and listening to make sure that the AHC pump has stopped. The ECU for the AHC system does not provide instantaneous pressures in real time but remembers the last pressures experienced by the system. So it is important to take the measurements correctly and repeat them say 3 times. Spurious measurements do arise from time to time. Note that the ECU does not provide pressures at each corner, just front and rear.

Your front and rear pressures are much higher than FSM recommendations and we will come to that later.

In your post #701, your mentioned of 3 graduation marks at the AHC tank when changing between “LO” to “HI”.

What does this mean?

At “LO” (compared to “HI”), there is decreased vehicle weight carried by the AHC system and more weight carried by the front torsion bars and rear springs. This is because when switched to “LO” the ECU causes valves to open. The vehicle sinks. The AHC system supports less weight. More weight is supported by the front torsion bars and rear springs. These become more compressed with the vehicle weight pushing down on them. Springs carry more weight in proportion to distance pushed down, just like a set of mechanical cooking scales. If all is well, the struts at each corner which look like shock absorbers are compressed and force fluid back to the AHC tank, also because the vehicle has settled at the “LO” position. At the same time, because the front torsion bars and rear springs are more depressed and are carrying more weight and the AHC system less weight, this allows the nitrogen gas pressure in healthy ‘globes’ to push on the flexible diaphragm inside the ‘globes’. This also forces some AHC fluid back to the AHC tank. The fluid level in the AHC tank rises.

[Note that the ‘globes’ are called ‘gas chambers’ in the FSM. Note also that the devices labelled ‘shock absorbers’ in the FSM are not what most people understand as ‘shock absorbers’ – in the AHC system these are merely hydraulic struts. The damping characteristics are achieved elsewhere – more about that later and in the attachments].

When “HI” is selected at the AHC switch, the ECU causes the height control accumulator to release its stored pressure and with some help from the AHC pump, AHC fluid is forced back into the AHC system to raise the vehicle. The hydraulic fluid pressure at the ‘globes’ also rises. Some fluid is pushed into the ‘globes’ against the diaphragm and the nitrogen pressure inside the ‘globes’. The fluid level in the AHC tank falls.

When the difference in the height test (moving between “HI” and “LO”) indicates only a small change in the volume in the AHC tank of less than 7 graduations, then unless there are major leaks or some other highly unusual fault, it indicates loss of nitrogen gas from the ‘globes’. Loss of nitrogen gas pressure in the ‘globes’ means that the diaphragm in unhealthy ‘globes’ will push less fluid back to the tank than healthy ‘globes when the “HI”/”LO” test is performed. Only 3 graduations is VERY low, much lower that the FSM-recommended minimum of 7 graduations and extremely low compared with the 14 graduations experienced with new ‘globes’.

So much for the “HI”/”LO” test and its purpose in diagnosis. What does it mean?

In the practical operation of the vehicle, the ‘globe’ at each corner (called a ‘Gas Chamber’ in FSM) is attached directly to a ‘Damping Force Control Actuator’ – see diagrams in the attachments. Together (and with help from other components in the AHC system) these devices perform the function of a shock absorber in a conventional suspension, but in far more elaborate way. This function is controlled by the AHC/TEMS Electronic Control Unit (ECU) which uses many inputs and constantly computes and varies the damping settings to match the driving conditions as best possible.

The system cannot work properly and damping will be poor when the ‘globes’ are in poor condition, as diagnosed by the “HI”/”LO” test. It means that the ride will be very bumpy, much like riding in vehicle with conventional suspension but with failed shock absorbers and negligible damping. If your ‘globes’ are measuring a “HI”/”LO” difference of 3 graduations, then your ‘globes’ are not in passable condition. They are ‘worn out’. This is natural. The membrane in the ‘globe’ deteriorates with age, the nitrogen under pressure is lost over time, and eventually the ‘globe’ is unable to perform its intended function. IH8MUD Members’ experiences with ‘globe’ lifetimes vary widely. As an example, I replaced all four ‘globes’ after 13 years and 183,000 kilometres (113,000 miles) when the “HI”/”LO” test showed a difference of 8 graduations. After replacement, my new OEM ‘globes’ showed a difference of +14 graduations in the “HI”/”LO” test.

What to do?

The many excellent posts in this thread boil down to this basic sequence:

• Continue pre-reading. Some attachments are offered which may help if not seen previously. Some references follow below to some essential and informative posts in this thread,

• Check that hardware on board the vehicle is in satisfactory condition. For the reasons explained above and as noted by Moridinbg at post #704 and Cetus at post #706, it appears likely that your ‘globes’ are in need of urgent replacement. Also, in your picture of the passenger side front suspension, the ‘shock absorber’ (actually a strut) has lost the upper protective cover. This may not matter much until dirt or salt or water work their way into the seals. As a starter, inspect the whole AHC system for visual condition and fluid leaks at all components and at all junctions with AHC pipework, inspect all electrical connectors for cleanliness, damage and security, and inspect all three height control sensors and their linkages. If there is doubt about condition of the sensors or linkages, remove, dismantle, inspect, and repair or replace if necessary – see link below,

• Replace components as needed where indicated by testing or observation. Enough already said or attached or linked about ‘globes’. Replacement is described in FSM – use “Search” to find the many IH8MUD posts on this topic. Assume that front torsion bars are in reasonable condition, do not require ‘re-indexing’ and that the adjusters work, not rusted up. Be suspicious of weak rear coil springs, especially if age is unknown. If in doubt, replace with correct OEM springs, or, consider upgrade of rear springs if heavy duty is required (such as King KTRS-79 springs but be aware that there may be some compromise in comfort), or, use spacers but note that there are different opinions about the usefulness of spacers,

• Bleed system after all new hardware has been fitted – the PADDO method is recommended,

• Check vehicle left-to-right cross-fall and correct excessive difference using torsion bar adjustment with the engine and ignition “OFF” so that the AHC system does not attempt to counter your adjustments. Note that in the AHC system torsion bar adjustments are used to correct cross-fall and they are used to adjust front AHC pressures. Unlike some other suspension systems, torsion bars are NOT used to adjust vehicle front height in the AHC system,

• With vehicle in the correct weight as nominated in FSM or with permanent accessories only, but no people, no load, full tanks of fuel, on level ground, front wheels pointing straight ahead, measure and record all hub-to-fender heights on the properly settled vehicle,

• Correct vehicle height using height adjusters. The engine and ignition must be “OFF” while making suspension adjustments for personal safety and so that the AHC does not work against you,

• With vehicle in the correct weight as nominated in FSM or with permanent accessories only, but no people, no load, full tanks of fuel, on level ground, front wheels pointing straight ahead, measure and record AHC pressures and other Techstream outputs or other electronic tester outputs, with at least 3 repeat measurements,

• Adjust front AHC pressures by transferring weight to or from the torsion bars using the torsion bar adjusters to achieve pressures in mid-range of the FSM specifications or a little lower – see attachment,

• Note also that if rear pressure adjustment is required, this cannot be done without the use of packers or new OEM springs or different springs with higher spring rates such as King KTRS-79. This may involve some compromise on comfort but some IH8MUD Members judge this to be worthwhile (including me) but depends on how the vehicle is intended to be used,

• Note that this may be an iterative process. Excessively high pressures may challenge the AHC system and encourage weeping at seals and other problems and cause a harsh ride. Excessively low pressures will mean that too much weight is being carried on the torsion bars and springs. Damping performance then will be poor and the ride will be bouncy.

• Note that large differences in height sensor readings may indicate a sensor fault, or, may indicate incorrect set-up of the vehicle, and resulting erroneous inputs to the ECU may affect suspension performance. Always correct cross-fall first using torsion bar adjusters, after that, adjust sensors to correct vehicle height, and after that, use torsion bar adjusters to bring front pressure into FSM-specified mid-range,

• The idea is to arrive at the ‘sweet spot’ with correct ‘Neutral Pressures’ with the vehicle at the correct weight (or at the usual operating weight if fitted with permanent accessories such as front and/or rear bars, sliders, winch, long range tanks, drawer system etc etc ) AND with the vehicle at the correct front and rear heights, AND with cross-fall corrected AND without major differences in height control sensor readings or major off-centre steering angle readings. This aim is to achieve best AHC performance and most comfortable ride. Note that pressure readings may not mean much and are not comparable with FSM ‘Neutral Pressures’ outside of the correct height and load conditions. AHC pressures, height and load are interdependent. Change the height or change the load and the AHC pressures also change.

• If considering a ‘lift’ as some Members have done, read IH8MUD extensively to benefit from their experiences.

As well as the attachments, reviewing the following UH8MUD references may be helpful.

Summary of PADDO replies collated by PabloCruise:
Definitive list of AHC maintenance items

The first ~7 years of the “Definitive List ….” from July 2012 to February 2019 is provided by tjb and can be downloaded at the following link. It is a big file – 28Mb and about 371 pages – but once downloaded it does make searching a bit easier and quicker, especially if internet is unavailable or signal is weak.
Definitive list of AHC maintenance items

A good discussion on height control sensors with guidance by uHu commences here:
Definitive list of AHC maintenance items

This post only provides a “Starter Pack”. There are plenty more contributions from Members under different headings in various IH8MUD threads. Persistent use of the “Search” function will reveal information and experience on most questions.

Go well!!

 

[Moridinbg]

Don't be super alarmed by the 3 graduations yet. Adjust your pressures first, THEN measure graduations. After adding a winch I "lost" 3 graduations, until I adjusted the torsion bars to compensate pressure.

 

[uHu]

Hi Azi,
Welcome from another student in this very useful “AHC Academy”!! I started only a short period of time before you and I sense your frustration. We have all been there!
......Go well!!

Wow Indro! This is a fantastic summary. I've been dreaming about condensing this long, unwieldy thread into a few pages containing all the important data, methods and tips; but this is a very good start.

 

[IndroCruise]

As far as I know the first sign of worn globes is that you can feel small road crack and things get bouncy, and I definitely do not have these problem.

Mmmmm -- "feeling small road crack and things get bouncy" can mean many things, not necessarily first sign of worn 'globes'. The "HI"/"LO" Volume Test -- how many graduations at AHC tank between "HI" suspension setting and "LO" suspension setting -- is a better indicator of 'globe' condition plus the 16 step test to investigate further. Anyway, your description indicates that other quoted measurements are in a good place and the vehicle is riding well.

It may be better to start with simple things ....

Weight:

See bottom of the second page in the "AHC - General Description and Diagrams" attachment to my post #711 in this thread yesterday. This extract from FSM describes the weight limitations of the AHC system. The system may not work properly beyond these limitations and in particular AHC may raise slowly or not at all.

Steering Angle:

As suggested by uHu, if the indicated steering angle is too far off-centre as measured by the steering angle sensor within the steering wheel assembly, erroneous signals may be received by the ECU and cause the AHC system not to work properly. Maybe off-centre is caused when steering alignment is done and a technician has applied unequal adjustments at the adjusters on the steering rack arms, without regard to centering the position of the steering wheel.

The comment by PADDO on resetting the steering angle sensor at post #526 in this thread also may help -- see this link: Definitive list of AHC maintenance items.

AHC Pump:

Previously, uHu provided information on AHC pump issues, and attached a Toyota Technical Service Bulletin (TSB) -- see this link: Definitive list of AHC maintenance items. When diagnosis suggests replacement is indicated, this TSB suggests replacing both the AHC pump and the AHC Height Control Accumulator. Expensive!!

The thread at the next link concerning AHC Pump replacement may be helpful. The thread also contains further guidance from uHu:
Finally fixed my AHC! Changed pump~

I also have a slowly raising system which may not fully raise and I have wondered whether my AHC Pump and/or Height Control Accumulator are showing their age -- almost 14 years but only 200,000 kms (124,000 miles). However, unlike your case, I have inconsistent height sensor readings and possibly inconsistent signals being received by the AHC ECU, so I need to sort that out first.

 

[Uwiik]

@Uwiik - If steering signal doesn't indicate somewhere close to center, the AHC will not rise to Hi.

thanks a bunch UHU!! This is what I need to hear. initially I suspected the steering angle sensor but eventually dismissed it and began suspecting other causes. Now with this information from you, I just have to have a 3 hours free time with my dad’s Cygnus (JDM LX470) without him being present to steal his steering angle sensor and test it on mine. The VGRS steering angle sensor is quite expensive, gotta make sure its the sensor itself and not the downline that’s causing the C1777 DTC before I throw money at it.
Again, thanks a lot UHU!!

 

[Uwiik]

Mmmmm -- "feeling small road crack and things get bouncy" can mean many things, not necessarily first sign of worn 'globes'. The "HI"/"LO" Volume Test -- how many graduations at AHC tank between "HI" suspension setting and "LO" suspension setting -- is a better indicator of 'globe' condition plus the 16 step test to investigate further. Anyway, your description indicates that other quoted measurements are in a good place and the vehicle is riding well.

It may be better to start with simple things ....

Weight:

See bottom of the second page in the "AHC - General Description and Diagrams" attachment to my post #711 in this thread yesterday. This extract from FSM describes the weight limitations of the AHC system. The system may not work properly beyond these limitations and in particular AHC may raise slowly or not at all.

Steering Angle:

As suggested by uHu, if the indicated steering angle is too far off-centre as measured by the steering angle sensor within the steering wheel assembly, erroneous signals may be received by the ECU and cause the AHC system not to work properly. Maybe off-centre is caused when steering alignment is done and a technician has applied unequal adjustments at the adjusters on the steering rack arms, without regard to centering the position of the steering wheel.

The comment by PADDO on resetting the steering angle sensor at post #526 in this thread also may help -- see this link: Definitive list of AHC maintenance items.

AHC Pump:

Previously, uHu provided information on AHC pump issues, and attached a Toyota Technical Service Bulletin (TSB) -- see this link: Definitive list of AHC maintenance items. When diagnosis suggests replacement is indicated, this TSB suggests replacing both the AHC pump and the AHC Height Control Accumulator. Expensive!!

The thread at the next link concerning AHC Pump replacement may be helpful. The thread also contains further guidance from uHu:
Finally fixed my AHC! Changed pump~

I also have a slowly raising system which may not fully raise and I have wondered whether my AHC Pump and/or Height Control Accumulator are showing their age -- almost 14 years but only 200,000 kms (124,000 miles). However, unlike your case, I have inconsistent height sensor readings and possibly inconsistent signals being received by the AHC ECU, so I need to sort that out first.

thanks for the insight Indrocruise!!

Actually you got a point there, I was able to get close to zero average value on all three sensors by tweaking and modifying the FL sensor. I ran out of threaded part on FL adjuster about 2mm before zero, I had to modify and lengthen the threaded part to achieve zero on FL sensor. After the mods on FL threaded part and able to achieve zero reading, the ride was totally transformed for the better but deep inside I knew that something was not right due to the fact that I had to modify FL sensor’s threaded part to achieve zero reading on N position, yet I chose to ignore it and bask in the comfort of the cruiser. And by the way, my cruiser is still totally stock with stock 18” rims and BFG tires, so no extra weight on it.

Just a couple of hours ago when playing with my truck I did notice that when on L position the height sensors reading are all over the place with large discrepancy between FL-FR sensors reading, it is only almost flat out equal on all three readings when on N position. I also did FSM procedure of 3 AA batteries voltage test on both FL-FR sensors and found out that both are showing different voltages to each other on Max H - N - Max L sensor arm position. Having found the spirit to work on the AHC again, today I also noticed that both my front height are not 50 mm / 19.5” anymore!!!! Both are 15mm lower!!! I did not notice it until today because the ride is still ooohhhh so comfortable I swear I did at least 10 L-N cycles with plenty of ride in between and always settling itself at 50mm/19.5” consistently when I last set it up a few weeks ago. Realizing what happened today, I think my case of slow raising AHC is similar to yours and it is about time for new sensors on all corners.

 

[shiretowndown]

My nagging "issue" with AHC is wondering if the suspension doesn't feel quite right. I feel bumps pretty well and I subjectively recall an older 100 series land cruiser standard suspension feeling like being on a cloud vs the small cracks in the road. The question is driving me insane when I'm on the road..

I've read what seems like every AHC topic on here over the past few months before and after my LX470 purchase. Knowledge is there but spread around.

I'd like to replace the major AHC wear items short of the globes and it would be very useful to confirm these steps in one post, for myself and others as well wondering about their suspension.

Here's what I've come up with for the most bang for the buck: please let me know if you'd add or remove anything / change ordering, etc. For the record, my LX is at 117k miles.


First you would want to diagnose if you have a problem with your AHC.
Unfortunately, the only test I know of is to check if your globes are bad via the "Height Test".
I have no way of knowing whether the other components are bad or if my ride is standard / okay. I just have a gut feeling that it can be improved. At worse, you'll be extending the life of your AHC by reducing wear on it.



AHC height test.
Put vehicle in LOW. Mark fluid level in AHC reservoir.
Put vehicle in HIGH.
Number of graduations (ticks) on the reservoir from LO to HI should be at least 7. If less, your globes are shot and it's very expensive to replace.

I personally get 14 or so so it appears they are in great condition.



Assuming those globes are fine, it's time to start working:



Flush AHC fluid.
AHC Fluid Change How To -- Need Input

Cost: $40 / can. Need 2.
Dealer charge around $200-250.
Difficulty: Easy.

Result: Many report increased ride quality. I didn't notice so much when the dealer did it. I am going to buy 2 cans and flush it till it's clean.




Test neutral pressure / crank torsion bars accordingly
Neutral pressure is the pressure of the AHC system at each wheel in the N position. The AHC system is designed to carry a certain load while the torsion bars in the front / coils in the rear pick up the rest.

My dealer refuses to check the neutral pressure for me saying it's only what crazy enthusiasts do so I've found a product called the Tactrix Open Port 2.0 which can read the pressures.

Once you have the pressures up front, you'll be able to crank the torsion bars until the AHC system is carrying the correct load. Others blindly do 3-6 cranks every 5 years.

Here's a post from somebody who cranked Tbars based on neutral pressure data: Measure AHC neutral pressure?

Cost: $100-200 used/new for Tactrix Open Port 2.0 Cable There's a $35 alternative discussed below; waiting for reports.
Cost at dealer: they cowardly refuse.
Result: Haven't done it yet. Hopefully noticeable.




Replace Rear Coil Springs
The neutral pressure test will probably show the rear AHC pressures too high due to age of the rear coils.

Posts on mud suggest 5 years max before rear AHC starts going over spec on load.

Anything else in this rear suspension setup I should replace?

Part numbers:
48231-6A730
48231-6A740

Cost: ~$200 for parts.
Cost at dealer / mechanic: ?
Result: haven't done it yet.




My hope is that after these changes I'll have done as much as I can (without spending too much) for my ride.

Any comments, additions, etc. appreciated.

Ok so the initial “AHC Height Test” I am really having a hard time seeing the correct line of my fluid level.
Are yall using a flashlight to backlight the tank or what?

 

[95Fantasma80]

Ok so the initial “AHC Height Test” I am really having a hard time seeing the correct line of my fluid level.
Are yall using a flashlight to backlight the tank or what?

Yes, same issue until i used a flashlight.

 

[Uwiik]

How important is it to maintain REAR height sensor reading to be as close as possible to the front? I can set my rear height to factory spec easily but on the position that give proper height the sensor reading is always far off from both front sensors.

I really am starting to really hate this AHC thingy, crazy never ending problems.

 

[uHu]

What??? If the car is on a level surface, (physical) heights and pressures in spec, and then move from Lo to N, all the 3 sensors should be at zero +/- 5 mm. That's the whole purpose of the AHC. What sensor height readings do you get?