AHC debug... won't go HI

TexFJ

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If the brake is on, AHC is supposed to not move heights. To move heights, put it in park, foot off brake. Hand brake should be ok.

If the car isn't totally on the ground, ahc isn't going to work and you should not cycle heights. If you're doing any other work on it and a wheel is in the air, wait until you've got it all back on the ground to troubleshoot ahc.
Sorry for the confusion...AHC Tests were done with wheels on ground. I just saw the HI LED functioning by accident when I had the wheels off ground and I turned the key, can't remember why.
 

TexFJ

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If you can find your year and model that's fine. I could never find a PDF other than the one jumbled 2004 version.
Neither can I find the PDFs... the stack is pretty impressive, never knew it added up to that many manuals.
 

TexFJ

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OK, fixed the issue....

IMG_9235.jpeg

I had a hunch it was the switch and it was. Tested conductivity and it was spotty.

Screen Shot 2020-05-25 at 2.18.14 PM.png


Cleaned up the connections under the rubber piece as well as the connectors with some electric cleaner and it started working.
Also, took the opportunity to check on that darn LED, since I think I have about 5 lights going out all over the place in the cabin. Noticed it was a crappy PCB trace, basically disconnected from the pad.
Screen Shot 2020-05-25 at 2.19.22 PM.png
Screen Shot 2020-05-25 at 2.23.53 PM.png
Screen Shot 2020-05-25 at 2.27.03 PM.png
scraped to access the trace then soldered.

 

TexFJ

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What's everyone's range for the suspension fluid level? I've heard some crazy numbers. Here is my N setting with the Hi and Low marked with tape. This is around 5 notches, but I've heard people saying it should be 8 and others that they get 14?!?! Perhaps the suspension fluid breaks down and changes its compressibility factor? I topped off with suspension fluid a week ago (about .7 L)

Screen Shot 2020-05-25 at 2.40.35 PM.png
 

suprarx7nut

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What's everyone's range for the suspension fluid level? I've heard some crazy numbers. Here is my N setting with the Hi and Low marked with tape. This is around 5 notches, but I've heard people saying it should be 8 and others that they get 14?!?! Perhaps the suspension fluid breaks down and changes its compressibility factor? I topped off with suspension fluid a week ago (about .7 L)

View attachment 2318594
The globes determine the fluid displacement. Before you do this test, you need to test and set heights and pressures. If the heights and pressures and good, your low gradation test probably means the globes are worn out and need replacement (they are a wear item so this is expected over time).
 

TexFJ

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Ok. Seems like I need to figure out why TechStream is showing 0 pressures.
Any downside in letting them fail? It’s all working now.
 

suprarx7nut

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Ok. Seems like I need to figure out why TechStream is showing 0 pressures.
Any downside in letting them fail? It’s all working now.
I'm not sure if it damages anything else, but it will probably ride very harsh. When you read about users stating ahc rides terribly, they're normally experiencing failed globes and/or badly degraded fluid.
 

ticoman

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If the brake is on, AHC is supposed to not move heights. To move heights, put it in park, foot off brake. Hand brake should be ok.

If the car isn't totally on the ground, ahc isn't going to work and you should not cycle heights. If you're doing any other work on it and a wheel is in the air, wait until you've got it all back on the ground to troubleshoot ahc.
Maybe it is a regional issue, here in Central America , if the E-brake is on AHC will not engage
 
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What's everyone's range for the suspension fluid level? I've heard some crazy numbers. Here is my N setting with the Hi and Low marked with tape. This is around 5 notches, but I've heard people saying it should be 8 and others that they get 14?!?! Perhaps the suspension fluid breaks down and changes its compressibility factor? I topped off with suspension fluid a week ago (about .7 L)

View attachment 2318594
 

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TexFJ

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Thanks @IndroCruise . Can you tell me the year and model for this FSM? I'm sure it's the same design through out the years but just curious.

Does Australia use a different suspension fluid as there is that difference?

For those getting 14, I guess that's OK as it falls under the "more" range :)
 
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Thanks @IndroCruise . Can you tell me the year and model for this FSM? I'm sure it's the same design through out the years but just curious.

Does Australia use a different suspension fluid as there is that difference?

For those getting 14, I guess that's OK as it falls under the "more" range :)
only use toyota fluid as ,stated on this forum it ruins the suspension
 

TexFJ

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only use toyota fluid as ,stated on this forum it ruins the suspension
I guess I'm just wondering what the diff is in the Aussie version. Sometimes different countries have different regulations on fluids, which may force the Toyota fluid to have different characteristics in different regions, etc. :hmm: someone may know.
 

suprarx7nut

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I guess I'm just wondering what the diff is in the Aussie version. Sometimes different countries have different regulations on fluids, which may force the Toyota fluid to have different characteristics in different regions, etc. :hmm: someone may know.
Might be labeling differences?
 
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I guess I'm just wondering what the diff is in the Aussie version. Sometimes different countries have different regulations on fluids, which may force the Toyota fluid to have different characteristics in different regions, etc. :hmm: someone may know.
Thanks @IndroCruise . Can you tell me the year and model for this FSM? I'm sure it's the same design through out the years but just curious.

Does Australia use a different suspension fluid as there is that difference?

For those getting 14, I guess that's OK as it falls under the "more" range :)
Thanks @IndroCruise . Can you tell me the year and model for this FSM? I'm sure it's the same design through out the years but just curious.

Does Australia use a different suspension fluid as there is that difference?

For those getting 14, I guess that's OK as it falls under the "more" range :)
Thanks @IndroCruise . Can you tell me the year and model for this FSM? I'm sure it's the same design through out the years but just curious.

Does Australia use a different suspension fluid as there is that difference?

For those getting 14, I guess that's OK as it falls under the "more" range :)
Suggest go to link to post by Moridinbg for FSM over various years.

The only AHC fluid I use is the genuine fluid supplied by Toyota and made by Japanese oil company Idemitsu Kosan Limited. There have been many warnings on IH8MUD about problems arising when substitute fluids have been used. The supply seems to come in different containers in different parts of the a world -- the pictures show the different types and also the part numbers to specify.

As others have mentioned, the "HI/LO test" provides a good indication of 'globe' condition because it measures fluid displaced by the 'globes' and sent back to the AHC tank at the "LO" setting compared with the "HI" setting. As the 'globes' age, the nitrogen pressure behind the diaphragm in each 'globe' is slowly lost. As pressure is lost, there less ability of the 'globes' to push fluid back to the tank. When 'globes' are new, expect around 14 graduations at the tank. This will decrease over time (years) and when the difference in graduations approaches 7 (or 8 in Australia), Toyota recommends replacement of all four 'globes'. Note that measuring AHC pressures tells you NOTHING about globe condition.

Probably you already understand the "HI/LO test" but just to explain in full again in case a new reader comes along .....

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 in the AHC system].

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 (or 8 in Australia), 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.

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 FSM documents. Together (and with help from other components in the AHC system) these devices perform the function of a shock absorber (or damper) 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 ‘globes’ are measuring a “HI”/”LO” difference of less than 7 graduations (8 graduations in Australia), then the ‘globes’ are not in passable condition. They are ‘worn out’. This is natural. The diaphragm 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 and the ride improved markedly

TOYOTA AHC FLUID 2-5litre CAN.jpg
TOYOTA AHC FLUID 1 litre plastic bottle.jpg
.
 
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TexFJ

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Great write up and a great point that we overlook, the variable pressure in the hydraulic system due to the springs/torsion bars doing more work in the low position.

I do have some questions that are still circling in my mind.

1) When you replaced the globes with OEM globes, they must have differed in the nitrogen pressure from the original OEM version of the globes. Otherwise I don't see an explanation in going from 7 (as designed by Toyota) to 14. That's a big difference. Unless your HI/LO dynamic range changed somehow from the stock version. Anyone else see this range increasing this much when replacing globes?

2) I believe you are missing one part of the system that could affect the graduations. The height accumulator also stores potential hydraulic energy which is released and used to speed up the the height adjustment. It has a free moving piston which is pushed by the hydraulic system to compresses nitrogen on the other side. It could be possible that the accumulator has failed (piston stuck or leaking nitrogen) and is no longer providing the extra hydraulic fluid to raise the car, hence more is needed from the reservoir, hence larger graduations.

3) 7/8 graduations is the minimum. Do we know what the graduation figure was for new LX470s coming off the assembly line?


P.S. I'm going to assume that the ECU programs are a little different in how they treat the LOW and HI in the Aussie version of the AHC, hence the difference between the 7 and 8. I can see that there is a global standard for the fluid now. It should all be incompressible hydraulic fluid that is friendly with the system.
 

uHu

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@TexFJ
Re your points 1 & 3: At least 14 grad's is the standard for new globes (or new LX470).
Re point 2: The state of the cylindrical accumulator might not come into play here, as it is assumed that it is pressurised to it's maximum (>10 MPa) both when the suspension is at Lo and at Hi, and therefore no fluid used. (Btw Just as the state of the 4 globe accumulators have no bearing on the pressures in the AHC system, the pressure at the cylindrical accumulator will still be the same whether it works or not.)

The 8 grad's for OZ and 7 for the rest of us, is only about TMC suggesting to the t0yota techs how to determine when to sell the customer new globes. 8 grad's will be the same whether it is in the US, OZ or even Norway.
 

TexFJ

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@TexFJ
Re your points 1 & 3: At least 14 grad's is the standard for new globes (or new LX470).
Re point 2: The state of the cylindrical accumulator might not come into play here, as it is assumed that it is pressurised to it's maximum (>10 MPa) both when the suspension is at Lo and at Hi, and therefore no fluid used. (Btw Just as the state of the 4 globe accumulators have no bearing on the pressures in the AHC system, the pressure at the cylindrical accumulator will still be the same whether it works or not.)

The 8 grad's for OZ and 7 for the rest of us, is only about TMC suggesting to the t0yota techs how to determine when to sell the customer new globes. 8 grad's will be the same whether it is in the US, OZ or even Norway.
Sounds like 14 grads it is... and I'm far from that.

Looking at the system diagram, I'm excluding the accumulator, it's the globes. As everyone has been telling me :)

The pump is only connected to the accumulator. When the height is changed, the height control valve assembly opens and lets the accumulator pressure start raising the car (front and back at once). The pump helps after the accumulator is emptied (one end at a time, back and forth) See my sped up video going from L to H.

Once the car is raised the pump continues to pressurize the accumulator for next time, while the height valve is closed allowing us to look at pressures at multiple sides of the valve.

IF the accumulator has leaked and there is either less nitrogen behind piston or fluid on the back side of the piston, then the pump still will pressurize and the car will lift, however that would affect both L and H and it wouldn't contribute to the delta in fluid level.

Long story short, I probably need to change the globes. :wrench::crybaby:💰

I saw someone cut open the globes... anybody seen a cut open accumulator?
Screen Shot 2020-05-27 at 10.27.40 PM.png
 
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Sounds like 14 grads it is... and I'm far from that.

Looking at the system diagram, I'm still not excluding the accumulator.

The pump is only connected to the accumulator. When the height is changed, the height control valve assembly opens and lets the accumulator pressure start raising the car (front and back at once). The pump helps after the accumulator is emptied (one end at a time, back and forth) See my sped up video going from L to H.

Once the car is raised the pump continues to pressurize the accumulator for next time, while the height valve is closed allowing us to look at pressures at multiple sides of the valve.

IF the accumulator has leaked and there is either less nitrogen behind piston or fluid on the back side of the piston, then the pump still will pressurize and the car will lift but the delta in fluid in the accumulator, hence the reservoir, will no longer be dramatic.

Not saying this is what is happening in my case, but just that a failed accumulator can lead to a smaller delta in fluid level between H and L. What is more reliable, a piston or a diaphragm? One thing I do know is that the globes get ALL the stresses from bumps and accumulator gets NONE, hence the diaphragm in the globes wear out tons more often than the accumulator piston. Long story short, I probably need to change the globes. :wrench::crybaby:💰

I saw someone cut open the globes... anybody seen a cut open accumulator?View attachment 2321315
Hi TexFJ,

You are right to consider the effects of the Height Control Accumulator and yes, the explanation in my previous post does assume that the Height Control Accumulator is operating correctly. My previous post really only describes some effects relating to new and worn ‘globes’.

So what happens if the Height Control Accumulator is not operating correctly?

You have put forward some ideas and uHu has replied very succinctly.

For me, the great benefit of this forum is that I get to learn from others. So I have laid out in detail my thinking and welcome review and correction from anyone, any where.

It seems useful to visualise and work through the whole AHC system by looking at the hydraulic circuit diagrams as shown in the last 4 pages of the attachment which describes the operation of the AHC and TEMS systems. These diagrams on the last pages show various operations with components in good condition. By the way, some cross-section diagrams of components also appear in this attachment. As requested, a cutaway picture of a 'globe' also is attached

Then it seems worthwhile to think about what happens in various fault or ‘worn out’ conditions.

To be of any use, the “HI/LO Test” must be carried out after the Height Control Accumulator and the AHC pump have completed their operations and are at rest. The FSM (see link to FSM offered in my previous post) suggests that the “HI/LO Test” be done at least 30 seconds after the “HI” indicator light has stopped flashing after an upwards movement. For my 2006 vehicle, I am suspicious about various parts of my AHC system because my vehicle raises and drops very slowly. So I try to make sure that the AHC pump has stopped and usually allow a minute or two just to be sure. The vehicle must be on a level surface. It also seems best that the vehicle be sitting at the recommended heights at each corner so that the pistons in the ‘shock absorbers’ are in the standard position at each AHC setting, “LO”, “N” and “HI”, and so that the pistons are sweeping the volume of fluid expected by the Toyota persons who designed the test as described in the FSM.

The “HI/LO Test” simply measures displacement of the hydraulic fluid from parts of the system under various conditions.

There are only three kinds of places from which fluid can be ‘displaced’ and move in any direction under pressure. These are

  1. the four ‘Shock Absorbers’,
  2. the four ‘globes’ (called ‘Gas Chambers’ in the FSM),
  3. the ‘Height Control Accumulator’,

Thinking about these one by one ….

The ‘Shock Absorbers” ….

The ‘Shock Absorbers’ are simple hydraulic struts which themselves contain no gas pressurisation. The piston inside each strut moves and the vehicle is raised or lowered according to the hydraulic pressure applied to them from other parts of the system and acting against the share of the weight of the vehicle carried by the AHC system.

Complete failure of the struts is rare although slow leakage or ‘weeping’ from struts sometimes is observed – meaning that the internal seals are leaking. This is seen on some older vehicles, or in vehicles where no steps have been taken to correct excessive hydraulic pressures which are substantially above the correct neutral pressures in the front or rear parts of system. These may be caused by long term or permanent heavy loads.

This happened to me! After fitting a heavy steel ARB Deluxe Bar (as seen in my avatar) I did not get around to sorting out the AHC pressures for almost two years. Eventually, the AHC pressures were corrected (using front torsion bar adjustment and new King KTRS-79 rear springs) and the front ‘shock absorbers’ were replaced. The original ‘shock absorbers’ were visibly damp but not dropping fluid and probably could have been left in place. I adopted a conservative approach to ensure reliability in a vehicle that travels long-distance through remote parts of Australia.

The ‘Globes’ ….

Effects from the four ‘globes’ (called ‘Gas Chambers’ in the FSM), were described in my previous post and in multiple IH8MUD posts by others.

If the diaphragm (meaning the resin membrane inside the ‘globe’) has failed and allowed gas pressure to escape, then there is nothing to drive or displace fluid from the ‘globes’.

Eventually, in the extreme case when ALL gas pressure is lost, fluid does not move out of the ‘globes’.

As the ‘globes’ slowly become ‘worn out’ over time (meaning that the gas pressure is slowly being lost over time), progressively there is less and less movement of the fluid from the ‘globes’ to the AHC tank when the “HI/LO Test” is conducted over the years. So fewer graduations at the AHC tank are seen in the “HI/LO Test” as time goes by.

This is why this test is used as a rough indicator of the condition of the four globes taken together. It does not distinguish the effects at any one ‘globe’ on its own. (The ’16 step test’ may give an indication of what is happening at each corner of the vehicle but differences could arise from many causes).

It is noteworthy that measuring AHC pressures – by electronic means including Techstream or by hydraulic gauge – cannot tell us anything about the condition of the ‘globes’.

The ‘Height Control Accumulator’ ….

If the ‘Height Control Accumulator’ has lost pressure or the piston is stuck, then the effect will be similar to a failed ‘globe’. In this situation, the Height Control Accumulator is then simply an inactive container in the AHC system. The hydraulic pressure and volume will be the pressure and volume provided by the AHC pump.

In the condition of a stuck piston or no gas pressure, there is nothing to drive fluid out of the Height Control Accumulator.

There would be no change in the volume of fluid in the Height Control Accumulator.

There would be no displacement of fluid from the Height Control Accumulator back to the AHC tank.

The changes in the fluid level at the AHC tank may then be less than they would be when the Height Control Accumulator is operating correctly.

The time to raise the vehicle from “LO” to “HI” would then be very long compare to FSM specification shown on the first page of the first attachment.

This is to be expected because in this condition of an inactive Height Control Accumulator, raising of the vehicle is driven only by the AHC Pump with no assistance from the Height Control Accumulator, so raising the vehicle will take much longer. It is likely that there also would be several Diagnostic Trouble Codes (DTC’s) occurring at that time -- see link from uHu with attached Technical Service Bulletin – but that is part of another different topic related to the AHC Pump.

Conclusion ….

Once the ‘Height Control Accumulator’ has stabilised and the AHC Pump has completed its cycle and the “HI/LO Test” is performed correctly, the test will indicate the condition of the ‘globes’. The ‘Height Control Accumulator’ will have no bearing on the “HI/LO Test” changes at the AHC tank, unless ‘Height Control Accumulator’ has a fault which causes it to perform erratically and inconsistently – for example, if it sometimes operates correctly and sometimes does not operate correctly. Repeated “HI/LO Tests” at the same time and in the same conditions and which showed variability in the changes in levels in the AHC tank may lead to suspicions about the condition of the ‘Height Control Accumulator’.

Comments, different views, different experiences, guidance, correction are all most welcome.

Late edit: I should add that I have no idea why the FSM sets a different threshold in the “HI/LO Test” for the replacement of ‘globes’ at 8 graduations in Australia versus 7 graduations for rest of the world. I have not found a Toyota Dealer nor Lexus dealer in Australia that can answer the question. Could it be that there are slightly different versions of the AHC/TEMS ECU firmware – and if so, why so? What about the LC100/LX470 versions sold in the much larger markets in Europe, Middle East, India, Russia, Africa, South America, etc, etc? Nobody seems to know and I doubt that it is worth worrying about too much. When approaching 7 or 8 graduations the ride quality is deteriorating and it is time to think about ‘globe’ replacement. AHC/TEMS is very rare on Toyota LC100 in Australia and was Iimited to top of line ‘Sahara’ (VX) versions from late 2005 until arrival of LC200. Lexus LX470 in Australia featured AHC/TEMS from the same time as the rest of the world (1999??) but the LX470 was considered a luxury vehicle and the numbers of LX470 in Australia are small. Many Australians who live, work or travel frequently in outback Australia prefer a Landcruiser with a conventional suspension, probably upgraded and possibly with a ‘lift’. The land area of Australia is about 11.5 times the size Texas but occupied by only 25 million people (less than the population of Texas) – so there is a lot of road between people and some roads are a little rough. Maybe Toyota thinks that we treat their vehicles a little more roughly than other people and that their vehicles need more protection or earlier maintenance!!

AHC Globe cutaway downloaded IH8MUD 22SEP18.JPG
 

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TexFJ

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Wow, this is a great document. Exactly what I hoped existed.

In my opinion your conclusion is spot on with regards to the accumulator.

One thing that I had trouble grasping is how big of a change in the # of graduations it took for Toyota to suggest replacing the Globes. But if you divide that fluid level by four globes then perhaps it shows Toyota expected the slow degradation in all 4 globes vs. a sudden failure in one.

With AHC, it is really important to understand how to debug the system and recognized how it's slowly/rapidly failing. As you do not want to start replacing components as it will get quite expensive fast. So these discussions help us work through different scenarios. (Why replace the globes when an accumulator is failing. Why replace the pump when the valve is failing, etc.)

The Service Bulletin does have me thinking if my accumulator's o-ring is failing and plugging up the pump as I'm getting the C1762 code, but the AHC still works. Then again, I'm not reading any pressures so hopefully it's just an electrical connection issue and the code is set due to 0 being 'an abnormal oil pressure'....

Time to find some globes...
 
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