The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (5 Viewers)

[yj668]

On the topic of AHC fluid, I'm dropping my data point:

I replaced all 4 factory globes a week ago and did the initial flush before globe R&R with 2.5 1L bottles that were bought Jan 2021 batches E8736 and E8737.
The fluid sat in my garage for a year so I filtered them with 2 layers of coffee filter and no gel was caught. They were not contaminated and my AHC pump's working well.

I cycled another 2x2.5L metal cans through the system to make sure the fluid's all fresh with new globes, AHC pump's still perfectly fine.

 

[Moridinbg]

Has anybody seen anything like this? I can read the Data List, can perform active tests with the solenoids, but I can't read & clear DTCs?! I get this error when selecting AHC from System Select & when trying to switch to Trouble Codes. This happened during the struggle with the pump and motor couple of weeks ago, immediately after trying to read the system with the solenoid block behind the accumulator disconnected.
The "Number of Trouble Codes" in the bottom of the Data List is cumulative - it keeps growing and survives battery disconnects.
The system is running & performing fine, but I can't see the error codes

I was hoping to find an AHC ECU to test with, but all I can get access to are pre-2002 (89290-60021), while I need 89290-60041 for post 2002.

 

[2001LC]

Has anybody seen anything like this? I can read the Data List, can perform active tests with the solenoids, but I can't read & clear DTCs?! I get this error when selecting AHC from System Select & when trying to switch to Trouble Codes. This happened during the struggle with the pump and motor couple of weeks ago, immediately after trying to read the system with the solenoid block behind the accumulator disconnected.
The "Number of Trouble Codes" in the bottom of the Data List is cumulative - it keeps growing and survives battery disconnects.
The system is running & performing fine, but I can't see the error codes

I was hoping to find an AHC ECU to test with, but all I can get access to are pre-2002 (89290-60021), while I need 89290-60041 for post 2002.

I saw something like this, kind of!

It was when I was testing AHC CPU with the older CPU 89290-60020 from 1998-99, in a 2001 that called for 89290-60021. I'd see the number of DTC as reported in AHC Data stream would double to 4, from the actual 2 DTC it did have. I could not open Trouble Codes from within AHC System, to read them with the older 89290-60020. The CPU in the 2001 (89290-60021) did test bad, but allowed me to open and read trouble codes.

So it would seem, you've issue with either Tech Stream. Which I've issue with my miniVCI, not letting me in Engine & ECT, DATA of the 200 series. But lets me in all other Engine & ECT buttons.
Or
Your AHC CPU has a fault.

 

[pbreisch]

started to get a rough ride today and ran tech stream, came up with these numbers:

Front Pressure - 7.5
Rear Pressure - 10.3
Accumulator Pressure - 10.4
Looks like the rear is way out of spec.


Current mileage is around 170k
I do have a Dissent rear bumper and swing out but I have King springs (Done 6-19-18) to help compensate.
AHC Fluid was refreshed using the Prado method at 154,800 miles (Done 10-28-17).
Up until today I had no complaints with ride quality.

Would you say it's time for new Globes? Do springs wear out that fast? I'm embarrassed to admit that other than 2 HIH and one trip out to Joshua tree this truck is primarily a commuter vehicle for me. So not worked too hard.

I'll add that the rear appears to be sitting real low, even when I cycle from L to N. It is late and the mosquitos are out so I can get more data tomorrow, but this is what I discovered today after work.

 

[IndroCruise]

started to get a rough ride today and ran tech stream, came up with these numbers:

Front Pressure - 7.5
Rear Pressure - 10.3
Accumulator Pressure - 10.4
Looks like the rear is way out of spec.


Current mileage is around 170k
I do have a Dissent rear bumper and swing out but I have King springs (Done 6-19-18) to help compensate.
AHC Fluid was refreshed using the Prado method at 154,800 miles (Done 10-28-17).
Up until today I had no complaints with ride quality.

Would you say it's time for new Globes? Do springs wear out that fast? I'm embarrassed to admit that other than 2 HIH and one trip out to Joshua tree this truck is primarily a commuter vehicle for me. So not worked too hard.

I'll add that the rear appears to be sitting real low, even when I cycle from L to N. It is late and the mosquitos are out so I can get more data tomorrow, but this is what I discovered today after work.

View attachment 3035311

Without meaning to offend, it helps if the complete Techstream screenshot can be shown. The pic given cuts off the line “Number of Trouble Codes”. Are there any DTC’s on this vehicle? If so, which ones?

The screenshot does show ….

• some differences in Height Control Sensor readings – not “near zero” but do not seem extreme – was the vehicle on a level surface at the time of the measurements?
• Front AHC pressure – OK
• Rear AHC pressure – way too high at 10.3 Mpa – has this been a long term pressure??
• Height Control Accumulator pressure – OK,
• IG and +B voltages – OK,
• Steering angle – not straight ahead (-554.50 degrees),
• AHC Fluid Temperature – seems hot at 138degF (Cause? Difficulties raising? Many Raise cycles?),
• Other switches and settings look normal.

Actual tape-measured hub-to-fender distances are not given at each wheel -- was the vehicle on a level surface at the time of the measurements? Has the vehicle been cross-levelled? Is the vehicle showing a ‘lean’ on a level surface? Is the vehicle height contributing to AHC over-pressure?

What time is taken to raise from "LO" to "HI"?

In answer to the question about KING KTRS-79 springs ….

No – the springs have not ‘worn out’ in only four years, especially given the light duty described.

In answer to the question about the ‘globes’ ….

One of the things to remember here is that the AHC pressures by themselves tell nothing about ‘globe’ condition. The weight of the vehicle is shared by Rear AHC system and coil springs at the Rear, and, shared by Front AHC system and torsion bars at the Front.

Even if the nitrogen pressures deteriorate, neither the share of weight carried by the AHC system nor the AHC hydraulic pressures change, not even if all ‘globes’ have failed completely, lost all nitrogen pressure, and filled completely with AHC fluid. This is because it is not the 'globes' but the AHC Pump which provides the hydraulic pressure to raise the vehicle to the selected "LO", "N" or "HI" height -- using the so-called 'shock absorbers' which actually are hydraulic struts.

There is no available method to measure directly the nitrogen pressure in a ‘globe’ to establish its condition – because the gas filling point is sealed and no valve is provided.

The ”HI-LO Test” (see FSM reference far below) is the only method Toyota/Lexus offer to test the overall condition of the ‘globes’ (altogether, not individually). This test relies on the displacement of fluid from the ‘shock absorbers’ measured at the AHC Tank between “HI” and “LO” heights remaining constant over time in a stock vehicle. However, as the years go by, the membranes in older ‘globes’ deteriorate, nitrogen pressure is lost gradually and so there is progressively less force behind the membranes to push fluid back to the AHC Tank in this test.

Over time (10+ years) fewer ‘graduations’ will be observed at the AHC Tank as a result of the declining contribution from the 'globes'. In this way, this test gives an indirect indication of the condition ‘globes’ (altogether, not individually).

When the difference in observed number of graduations is around 14, the ‘globes’ are as new; when the observed number of graduations falls to 7 or less, with the AHC pressures within the FSM-specified ranges, then the FSM recommends change-out of all four ‘globes’. Usually, steadily deteriorating ‘ride quality’ also will be noticed as the ‘globes’ approach this point. Yes – it is possible that only one or two ‘globes’ have failed on a vehicle, but like other ‘wear’ parts such as tyres, brakes, etc – when one is worn, usually the others are not far behind. Note that when AHC pressures are not in the FSM-specified ranges, then the results of this test are not comparable with FSM numbers.

All that said, if the ‘globes’ are original or 10+ years old and/or if the ‘globes’ have been subject to ongoing extreme AHC pressures on the fluid side due to heavy loads, then earlier than usual deterioration of membranes in the ‘globes’ and valves throughout the AHC system must be expected. It is possible for final membrane rupture to seem sudden, although the weakness will have been developing over a long period.

So new ‘globes’ may be in your future anyway.

As mentioned, the Rear AHC pressure of 10.3 Mpa is very high, compared to the FSM-specified range of 5.8 Mpa to 6.7 Mpa – especially when KING KTRS-79 coil springs have been fitted.

In my own case, after I fitted KING KTRS-79 rear coil springs to my 2006 HDJ100R, my rear AHC pressure was around 5.1 Mpa, even with a tow-bar and a single KAYMAR swingout and an additional spare wheel on board.

Where to look? More information is needed for diagnosis but here are some thought-starters:

Vehicle Load:

• Check Front and Rear Mass (weight) on a weighbridge,

Mechanical:

• Check under vehicle for any item which may restrict or affect free movement of suspension,
• Correctly seated springs,
• Worn or frozen bushings at all rear suspension connections, especially rear upper and lower control arms and panhard rod,
• Damaged or rusted shock absorbers,
• Interference between coil springs and internal air-assist bags (if fitted),

Electrical:

Regardless of whether a DTC is present or not:

• Test Pressure Sensor per FSM,
• Test Rear Height Control Sensor per FSM,
• If still unresolved, consider other conditions (DTC's?) which may indicate partial blockage at AHC Pump or in lines which may have built up over time

FSM references:

Check load load limits of AHC/TEMS system:

LC100 Workshop Manual - https://lc100e.github.io/ then scroll through tabs at LHS panel on opening page:
+ New Car Features,
+ Chassis,
+ Suspension,
+ Active Height Control Suspension and Skyhook TEMS

At this 20 page extract, see AHC load limits described for stock vehicle at the foot of Page 197. Upgraded springs at Rear and torsion bar adjustments (or re-indexing in some cases) is required to carry heavier loads and maintain AHC operation and reasonable TEMS damping performance

Cross-level front of vehicle:

LC100 Workshop Manual - https://lc100e.github.io/ -- then scroll through tabs at LHS panel on opening page:
+ Repair Manual,
+ SUSPENSION AND AXLE,
+ ACTIVE HEIGHT CONTROL SYSTEM
+ ADJUSTMENT -- Page SA-313 -- Cross-level Front of vehicle

“HI/LO Test to check overall condition of ‘globes’:

LC100 Workshop Manual - https://lc100e.github.io/ -- then scroll through tabs at LHS panel on opening page:
+ Repair Manual,
+ SUSPENSION AND AXLE,
+ DAMPING FORCE CONTROL ACTUATOR,
+ ON-VEHICLE INSPECTION – Page SA-338 – Inspect gas chambers a.k.a. ‘globes’

Check Pressure Sensor and
Check Rear Height Control Sensor

LC100 Workshop Manual - https://lc100e.github.io/ -- then scroll through tabs at LHS panel on opening page:
+ Repair Manual,
+ DIAGNOSTICS,
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS,
+ C1713 – Rear Height Control Sensor Circuit – Page DI-224
+ C1718 – Fluid Pressure Sensor Circuit – Page DI-4 or DI-229 (note two different connectors)
+ Other conditions and DTC's which may be suggested by observed symptoms,

Note description of ‘fail safe function’ in all of the above items. Which of these match the observed symptoms?

 

[pbreisch]

• some differences in Height Control Sensor readings – not “near zero” but do not seem extreme – was the vehicle on a level surface at the time of the measurements?

I am going to start trouble shooting this live today. I am measuring all this in my neighborhood street, it is level enough that it passes the Vehicle in N with no brakes and it doesn't move test. It might have a slight crown, but I believe most people would call it a level street.

• Rear AHC pressure – way too high at 10.3 Mpa – has this been a long term pressure??

I don't know, the ride was pretty good up until yesterday, that prompted me to dig up the old tech stream cable. The last time I checked was years ago.

• Steering angle – not straight ahead (-554.50 degrees),

My wheels were turned, I've corrected that below.

• AHC Fluid Temperature – seems hot at 138degF (Cause? Difficulties raising? Many Raise cycles?),

Could be two fold, it was 95 degrees yesterday and I had done repeated attempts at raising and lowering the vehicle to try and figure out what was going on.

Actual tape-measured hub-to-fender distances are not given at each wheel -- was the vehicle on a level surface at the time of the measurements? Has the vehicle been cross-levelled? Is the vehicle showing a ‘lean’ on a level surface? Is the vehicle height contributing to AHC over-pressure?

Measurements as of this morning in N:
Cold, undriven:
FL - 19 1/8"
FR - 20"
RR - 18 1/2"
RL 18 1/8"

After driving aprox. 1 Mile:
FL - 19 3/8"
FR - 20"
RR - 18 1/2"
RL - 18 1/8"

The rear is sitting noticeably lower than it should be, this was not the typical ride height before this problem popped up.

Attached is the tech stream screen while doing those readings:

What time is taken to raise from "LO" to "HI"?

When trying to raise the vehicle from N to H the rear raised significantly but the front remained low. The AHC light in dash flashed in the H spot then returned to a solid Green N. This resulted in the following measurements:

FL - 19 1/4"
FR - 20"
RR - 25"
RL - 24 1/2"

It took 50 seconds from L to a flashing H to a solid N with the rear raised up.

----------------------------

At this point my battery on the laptop died so I had to come in and charge it. I am going to let it charge a bit and run a cord out to the street so I can continue working, but these are my findings so far.

Suggested trouble shooting order:

Vehicle Load:

• Check Front and Rear Mass (weight) on a weighbridge,

I have Dissent bumpers front and rear. I have removed the 3rd row seats and replaced them with a simple plywood rear shelf with a Dometic fridge on it. I also have metal tech sliders. So I do have some extra weight but not fully loaded like an expedition truck. I do have King Springs to makeup for the added weight in the rear.

While my laptop charges I will read through some of the supplemental test info.

 

[pbreisch]

Ok, well, I think I might have found the problem. The rear height sensor was broken off it's mount. Must have either rusted through or been hit by some road debris. Time to order a new one and cross my fingers. Any opinion on OEM vs Aisin?

Also, no matter what brand I pick it's going to be a few days before I can get this part. Anything I can do to get this into a "limp" mode so I can drive to and from work? If I disconnect the plug and remove the sensor will it ride at N setting without height control or will that mess something up?

 

[IndroCruise]

Ok, well, I think I might have found the problem. The rear height sensor was broken off it's mount. Must have either rusted through or been hit by some road debris. Time to order a new one and cross my fingers. Any opinion on OEM vs Aisin?

Also, no matter what brand I pick it's going to be a few days before I can get this part. Anything I can do to get this into a "limp" mode so I can drive to and from work? If I disconnect the plug and remove the sensor will it ride at N setting without height control or will that mess something up?

On physical hub-to-fender heights measured with a tape measure:

The measured side-to-side Front heights (Front Left to Front Right) are not within the FSM tolerance for cross-levelling. This may only be due to road camber, small as that may be, if measurements were taken in the street. Suggest take measurements on a garage floor, or floor in a carpark under a building, or anywhere you can be reasonably sure that a constructed floor is level, not in a street nor anywhere that has a significant fall for drainage purposes.

If the differences in Front side-to-side tape measurements are confirmed, then adjust at the Front using the torsion bar adjusters per FSM explanation.

The standard hub-to-fender heights favoured by IH8MUD members for a stock vehicle regardless of tyre size are

Front: 19.75 inches (both sides)
Rear: 20.50 inches (both sides).

These are not FSM specifications but are easily measured and widely used approximations which are good for most purposes, much less fiddly to measure than the FSM-prescribed dimensions. The numbers will be different for a vehicle which has been lifted.

On an AHC-equipped vehicle, ‘ride height’ at “N” selected height is set or adjusted by moving the Height Control Sensor adjusters, and not the torsion bar adjusters.

The FSM-indicated time to raise “LO” to “N” and raise from “N” to “HI” should be about 15 seconds for each step (“LO” to “N”, then “N” to “HI”) for a new and healthy stock vehicle. Your raise time from “LO” through “N” to “HI” of about 50 seconds seems reasonable, given age and weight of the vehicle, and suggests that the AHC Pump still is capable of doing its job. Be aware that the AHC Pump (which is a small positive displacement gear pump) does wear and does have internal strainers which can be prone to blockage. This is a robust long-life pump but eventually some diminution of pump performance is inevitable. Longevity is enhanced by regular changes of AHC Fluid at least in line with the frequencies in the Owner’s Manual (earliest of 60,000 miles or 6 year intervals) but better if more like 30,000 miles or 3 years, and, by keeping AHC pressures under control. AHC Pump replacement is neither difficult nor expensive, if and when required.

Your tape measurements at the Rear at “N” suggest that the Rear of vehicle is at “LO” height regardless of the height setting at the console switch. Suggest check visually to see whether the Rear of the vehicle is resting on the bump stops. At “LO” it should ride above the bump stops but there will not be much clearance.

The symptoms -- posture and behaviour of the vehicle -- are consistent with a failed Rear Height Control Sensor.

However, please be aware that if the Front Height Control Sensors are of similar age, they are not beyond suspicion as well.

Best to start with replacement of the known damaged Rear Height Control Sensor, then review vehicle behaviour and symptoms.

As noted in other Posts, absence of Height Control Sensor DTC’s (C1711, C1712, C1713) does not provide assurance of healthy Sensors.

If this was my vehicle, I would be prepared to drive it carefully at town speeds on sealed roads avoiding rough surfaces, while waiting for a few days for the replacement Sensor.

You could try using a cable tie or similar to position the Rear Sensor arm in mid-swing (corresponds to “N” height if the Sensor is electrically healthy). This may give some strange effects. Personally, I don’t think I would bother – but there is no downside to trying this to see if it works as a short term workaround.

On Height Control Sensors:

Suggest read the two links at the bottom of the thread at this link:

03 LX470 AHC issue, shop diagnosis? - https://forum.ih8mud.com/threads/03-lx470-ahc-issue-shop-diagnosis.1286612/#post-14482522

This goes to IH8MUD Posts containing some detailed explanation, Part Numbers and pictures concerning Height Control Sensors – this is easier and quicker than me writing out the same information again.

On Vehicle Weight and Load:

The vehicle as described would be fairly heavy and would be close to GVWR after passengers and other loads are added. The AHC/TEMS should still cope given the upgrade with KING KTRS-79 rear springs to ease Rear AHC pressures and with torsion bar adjustment to ease Front AHC pressures.

On Aisin versus Toyota/Lexus Parts:

I bought the Rear Sensor seen in the picture found via the above link as a Toyota/Lexus Part Number from Partsouq -- but it is stamped "AISIN". This no surprise -- AISIN is a major supplier to Toyota/Lexus --and Toyota is a significant investor in AISIN!! Direct purchase from AISIN may be cheaper.

Suggest stay with genuine Aisin or genuine Toyota/Lexus Sensors, sourced from whereever you can get them at a reasonable price – there have been many unhappy IH8MUD reports concerning other substitutes – best avoided.

On the Techstream screenshots:

The second screenshot shows Height Control Accumulator pressure of zero. This may only mean that the measurement was taken too quickly, before the Height Control Accumulator had been recharged, which happens at the end of the raise cycle. Allow 30 to 60 seconds after the dashboard AHC light has stopped blinking and then be quite sure that the AHC Pump has stopped before taking AHC Pressure measurements. Otherwise, non-operation of the Height Control Accumulator may indicate that there is another problem to pursue.

Both screenshots show very high Rear AHC pressures of 10.3 Mpa and 10.4 Mpa. This is puzzling when the Rear of the vehicle is low and so the Rear AHC pressure actually should be low. Sadly, this may indicate that there are other problems. Hopefully these readings are due only to inconsistent signals being received by the AHC Electronic Control Unit (ECU) from damaged Height Control Sensor(s) and causing aberrant behaviours.

Best to start with the obvious replacement of the Rear Height Control Sensor and go forward from there.

 

[IndroCruise]

Has anybody seen anything like this? I can read the Data List, can perform active tests with the solenoids, but I can't read & clear DTCs?! I get this error when selecting AHC from System Select & when trying to switch to Trouble Codes. This happened during the struggle with the pump and motor couple of weeks ago, immediately after trying to read the system with the solenoid block behind the accumulator disconnected.
The "Number of Trouble Codes" in the bottom of the Data List is cumulative - it keeps growing and survives battery disconnects.
The system is running & performing fine, but I can't see the error codes

I was hoping to find an AHC ECU to test with, but all I can get access to are pre-2002 (89290-60021), while I need 89290-60041 for post 2002.

Don't know -- but would be very suspicious of ECU when presented with memory faults. The FSM is vague ....

 

[Moridinbg]

Don't know -- but would be very suspicious of ECU when presented with memory faults. The FSM is vague ....

I saw something like this, kind of!

It was when I was testing AHC CPU with the older CPU 89290-60020 from 1998-99, in a 2001 that called for 89290-60021. I'd see the number of DTC as reported in AHC Data stream would double to 4, from the actual 2 DTC it did have. I could not open Trouble Codes from within AHC System, to read them with the older 89290-60020. The CPU in the 2001 (89290-60021) did test bad, but allowed me to open and read trouble codes.

So it would seem, you've issue with either Tech Stream. Which I've issue with my miniVCI, not letting me in Engine & ECT, DATA of the 200 series. But lets me in all other Engine & ECT buttons.
Or
Your AHC CPU has a fault.

So I went and did a Health Check where it reads all systems. It didn't complain about AHC and showed no DTCs. Then I cleared all DTCs for all systems from the Health Check screen. And now I can read AHC Trouble Codes again! The cumulative Number of Trouble Codes is down to zero. Previously, as the Trouble Codes screen for AHC was not loading, I could not clear the AHC DTCs. Clear all from the health check did it.

It never presented a memory fault, but you gotta love the diagnostic steps for that - Turn the car off and back on. If issue persist - go buy a new ECU

 

[wrigh003]

So- this isn't necessarily a "how to bleed/ update/ refresh the AHC" comment, because I've done that, and it's all working good. No fluid leaks, there's little or no air in system now. This is more of a ... "how does this thing really work" question.

Went out wheeling this past week. I have an almost stock 99 LX470 and the only other thing added related to the AHC is a Slee AHC disconnect switch. As I understand, all that really does is remove the wheel speed sensor input and thus keep it in high if you have it set there. Problem- it wasn't really consistently working. I could always get it to go back up, if I asked it to and conditions were OK for it, but the question I have this this:

Does anything BESIDES wheel speed input cause AHC to sense that it needs to drop from high to neutral? Any suspension sensors or other things (vehicle attitude sensor/ something like) that would cause it to drop down? It was pretty frustrating to be in the middle of a rock garden and realize that the little lift I thought I had went away somewhere and then have to wait for it to go back up, or just bash through. Glad I got my rock sliders in...

 

[vcheng]

Does anything BESIDES wheel speed input cause AHC to sense that it needs to drop from high to neutral? Any suspension sensors or other things (vehicle attitude sensor/ something like) that would cause it to drop down?

The VSS above 18 mph.

 

[pbreisch]

finally got my rear height control sensor and slapped it in the truck. Set the adjustment bolt as close to center as I could eyeball and fired up tech stream.

Here’s the numbers.

I’ve cross leveled the front but looks like I will need to tighten down the TBars to get the front in spec but the rear looks good. If anyone else has a dropped rear end with high pressures like I was seeing I would suggest first thing would be to check the integrity of the rear sensor.

 

[udubfl]

Did the ABC last week due to real bouncy ride. Made some adjustments to torsion bars, got the heights and pressures to spec but graduations was less than 7 and still bouncy. Determined my globes were bad. Got my new globes and replaced them this weekend. It included another flush with the new globes. Lots of bubbles. Guessing it’s from nitrogen leaking from 3 out of 4 globes. Just guessing three were bad because after taking off the globes, more bubbles were coming out the globe like if you were doing a leak test on a tire or gas line with soap. Two of three globes failed the “pencil test” but one of it passed but still think it’s bad cause the bubbles kept coming out when I left it alone with oil sitting in the reservoir.


Here’s one of the globe’s flush. 3/4 being bubbles.

I can report that bouncy effect is gone along with the bubbles during the final flush. Will be checking the pressure and height again in few days.

 

[2001LC]

finally got my rear height control sensor and slapped it in the truck. Set the adjustment bolt as close to center as I could eyeball and fired up tech stream.

Here’s the numbers.View attachment 3042267 I’ve cross leveled the front but looks like I will need to tighten down the TBars to get the front in spec but the rear looks good. If anyone else has a dropped rear end with high pressures like I was seeing I would suggest first thing would be to check the integrity of the rear sensor.

View attachment 3042269

View attachment 3042270

View attachment 3042271

Were the ball joints of sensor arm frozen in place?

 

[IndroCruise]

Did the ABC last week due to real bouncy ride. Made some adjustments to torsion bars, got the heights and pressures to spec but graduations was less than 7 and still bouncy. Determined my globes were bad. Got my new globes and replaced them this weekend. It included another flush with the new globes. Lots of bubbles. Guessing it’s from nitrogen leaking from 3 out of 4 globes. Just guessing three were bad because after taking off the globes, more bubbles were coming out the globe like if you were doing a leak test on a tire or gas line with soap. Two of three globes failed the “pencil test” but one of it passed but still think it’s bad cause the bubbles kept coming out when I left it alone with oil sitting in the reservoir.


Here’s one of the globe’s flush. 3/4 being bubbles.
View attachment 3043263

I can report that bouncy effect is gone along with the bubbles during the final flush. Will be checking the pressure and height again in few days.

Great work! Your good diagnosis has given you a great result! That was one helluva a lot of gas which came out of the system – sure looks like ‘globe(s)’ were way, way past their use-by date and were letting the nitrogen go big time.

One small detail – and this is a general rant – certainly not aimed at your Post ….

Suggest beware of the so-called “pencil test”.

In some posts by others it is misunderstood or over-used. The “pencil test” does help to tell whether the membrane has failed and the pressure behind the membrane is non-existent or very, very low because the nitrogen behind the membrane has departed or is well on its way. If the nitrogen has come out in large quantities, then fluid will have found its way in past the membrane to the gas side. This will then look like a loss of fluid at the AHC Tank. [This a simple system – there are only two places to look for lost fluid: (1) Leaks, and (2) Inside the ‘globes’ behind the membrane]. The membrane might then be sitting deep towards the back of the ‘globe’ or it may be seem very soft and squishy and can be pushed easily. In either case, the “pencil” then goes very deep against extremely low or no pressure resistance.

Beyond that, the “pencil test” tells absolutely nothing about the condition of a partly used ‘globe’ in fair condition.

The following numbers explain ….

New ‘globes’ ex-factory are specified (see FSM) to have been filled with nitrogen at 327 psi (front) and 384 psi (rear).

When the attached FSM-specified test procedure is used to check overall condition of the four ‘globes’ on the vehicle at correct AHC fluid pressures, expect 14 graduations of difference in fluid levels at the AHC Tank.

When this declines to 7 graduations, the FSM recommends change out all ‘globes’ – too much nitrogen pressure has been lost, probably over 10 or more years, damping performance is seriously impaired -- rough ride.

What then is the remaining nitrogen pressure behind the membrane? It is not measurable and it may not be linear with the measured reduction in fluid volume – meaning that it is not clear whether the nitrogen pressure at 7 graduations has fallen to around 150 psi (say half the factory fill pressure). Whatever, it still will be a big number, for example, more than three maybe four times the pressures that most people use in tyres on a sealed highway.

The ‘globe’ in the bottom right of the pic below came off a vehicle still showing 8 graduations – changed out a little early prior to a major cross-country trip.

The “button” in the centre of the membrane can be seen in the expected position just below the fluid entry passage into the ‘globe’.

The “button” is not going anywhere – even with a mighty push on any “pencil” against (say) 150 psi nitrogen remaining pressure behind the membrane!

The point is that using the "pencil test" to indicate remaining 'globe' pressure and condition makes even less sense than checking the pressure of a large road tyre by pushing a pencil against the sidewall, even with only 40 psi behind it.

The “pencil test” is only a "depth gauge", definitely not a “pressure tester” and not even a useful indicator of remaining nitrogen pressure in a ‘globe’ in fair condition.

 

[udubfl]

@IndroCruise, great reminder on the pencil test. I know these globes are expensive but since there’s real no good way to test these and even if they are good, it’s matter of time when it will go, so I went with new ones to get some peace of mind (IMPEX made it worthwhile vs paying dealer price).

Case in point, I bought my 99 LX (195k miles) earlier this year after totaling my LC. So, new to AHC world. Based on a invoice/receipt, previous owner had 4 globes replaced by independent shop in 2018 and 20k miles ago but the globes were used and was provided by the PO. Indie charged them $600 for labor and fluid.

One other point that I noticed during the replacement. Previous work had the globes on wrong place. On driver side, they put the larger globe (500) on front and smaller one (400) in back. I could see myself not paying attention and doing this too during install. So, got that straightened out as well.

 

[IndroCruise]

@IndroCruise, great reminder on the pencil test. I know these globes are expensive but since there’s real no good way to test these and even if they are good, it’s matter of time when it will go, so I went with new ones to get some peace of mind (IMPEX made it worthwhile vs paying dealer price).

Case in point, I bought my 99 LX (195k miles) earlier this year after totaling my LC. So, new to AHC world. Based on a invoice/receipt, previous owner had 4 globes replaced by independent shop in 2018 and 20k miles ago but the globes were used and was provided by the PO. Indie charged them $600 for labor and fluid.

One other point that I noticed during the replacement. Previous work had the globes on wrong place. On driver side, they put the larger globe (500) on front and smaller one (400) in back. I could see myself not paying attention and doing this too during install. So, got that straightened out as well.

You are on top of this @udubfl. It definitely is a good idea to change out the 'globes' with new replacements correctly fitted as you have done. As you mention, there is no way to ascertain the condition of used 'globes' individually by looking at them and using the "pencil test" -- unless the 'globes' have completely failed -- and then what is the point, replacement is essential anyway.

These notes may help others who come this way in their searches through the various AHC threads:

One of the things to note here is that the AHC pressures by themselves tell nothing about ‘globe’ condition.

The weight of the vehicle is shared by Rear AHC system and coil springs at the Rear, and, shared by Front AHC system and torsion bars at the Front.

Even if the nitrogen pressures deteriorate, neither the share of weight carried by the AHC system nor the AHC hydraulic pressures change, not even if all ‘globes’ have failed completely, lost all nitrogen pressure, and filled completely with AHC fluid.

This is because it is not the 'globes' but the AHC Pump which provides the hydraulic pressure to raise the vehicle to the selected "LO", "N" or "HI" height -- using the so-called 'shock absorbers' which actually are hydraulic struts in AHC-equipped vehicles. The hydraulic pressure is held in place by the Levelling Valves in the Control Valve Assembly. These are normally closed, and only open when directed by the AHC Electronic Control Unit (ECU).

There is no available method to measure directly the nitrogen pressure in a ‘globe’ to establish its condition – because the gas filling point is sealed and no valve is provided.

The ”HI-LO Test” (see FSM reference attached previously in Post #276 in this thread and elsewhere) is the only method Toyota/Lexus offer to test the overall condition of the ‘globes’ (altogether, not individually). It is an easy, simple test.

This test relies on the contribution of fluid from the ‘shock absorbers’ at the AHC Tank between “HI” and “LO” heights remaining the same over time in a stock vehicle.

However, as the years go by, the membranes in older ‘globes’ deteriorate, nitrogen pressure is lost gradually and inevitably, and so there is progressively less force behind the membranes to push fluid back to the AHC Tank in this test.

Over time (10+ years) progressively fewer ‘graduations’ will be observed at the AHC Tank as a result of the declining contribution from the 'globes' in this test.

In this indirect way, the purpose of this test is to give an indication of the condition of the ‘globes’ (altogether, not individually).

When the difference in observed number of graduations is around 14, the four ‘globes’ altogether are as new; when the observed number of graduations falls to 7 or less, with the AHC pressures within the FSM-specified ranges, then the FSM recommends change-out of all four ‘globes’.

Steadily deteriorating ‘ride quality’ also occurs as the ‘globes’ approach this point -- but this can be so slow and gradual that it may not be noticed until it is really obvious.

Yes – it is possible, even likely, that only one or two ‘globes’ have failed completely before the others on a vehicle, but like other ‘wear’ parts such as tyres, brakes, etc – when one is worn, usually the others are not far behind – so when one ‘globe’ is in poor condition, replacement of all four ‘globes’ makes good sense. Note that when AHC pressures are not in the FSM-specified ranges, then the results of this test are not comparable with FSM numbers.

All that said, if the ‘globes’ are 10+ years old, OR, if the ‘globes’ have been subject to ongoing extreme AHC pressures on the fluid side due to heavy loads in or on the vehicle, then deterioration of membranes in the ‘globes’ and valves throughout the AHC system must be expected.

It is possible for final membrane rupture in a ‘globe’ to seem sudden, although the weakness and loss of nitrogen pressure will have been developing over a long period (years).

Nowadays, ‘globe’ replacement is not prohibitively expensive with good pricing (around USD600 for new OEM Toyota/Lexus set of 'globes', inclusive of 2 x Front 49141-60010 and 2 x Rear 49151-60010) from IMPEX and Partsouq and elsewhere. Replacement is not a difficult or lengthy DIY job and/or can be done by an independent mechanic. Many IH8MUD posts describe practical and safe procedures.

Once done, the important thing is to set the desired 'ride height' at "N" (using Height Control Sensor adjusters, not torsion bar adjusters), then measure the AHC hydraulic pressures at Front and Rear, using Techstream, ELMscan or some other scanner, and then take action to adjust these pressures so they are within the FSM-specified ranges. If AHC pressures are too high or too low, then the real-time, automatically-adjusting (over 16 steps) damping performance of the Toyota Electronic Modulated Suspension (TEMS) system will be poor and ride quality will be disappointing.

The next step – or maybe it is the first step – is to inspect and if necessary replace all worn bushes in all mechanical parts of the suspension and check ball-joints and check adjustment of front wheel bearings. These all make a difference to ride quality.

 

[wrigh003]

It's good to see other people going through this stuff - one of the reasons I like this place so much.

I've been slowly pecking away at getting the AHC right in mine for months. Swapped globes, flushed fluid, adjusted pressures with torsion bars, etc. The very last bit of the actual AHC and pressures is going to be rear spring spacers to take up the slack from the sagged old ones, balance pressures, and then probably one last bleed/ flush. Am I spending a few extra bucks on hydraulic fluid? Probably. Is it getting better every time I touch it still? Yes, lol.

Bleeding mine with a vacuum bleeder last week was a big step up in ride quality. After changing out the globes I was pretty annoyed to find that there wasn't THAT big an increase in ride quality, but it wasn't $600 wasted. They have 12-13 gradations now instead of 7, so those are improved and new and hopefully still good for another 20 yrs like the first ones. I think a long time period of having failed or failing globes in circulated a BUNCH of air (or nitrogen, whichever) up into the system, and that all didn't come out on first pass of just a regular "crack bleeders and hopefully the air comes out" process. So actively pulling it out with an air tool helped.

Overall - I guess just for those who are going "dammit, it should ride better now..." just keep poking at it. It's a great system when it runs right and I feel it's worth the irritation and fiddling to restore. And as Indrocruise notes - once the AHC is as it should be, or while doing it, look at all the bushings, body mounts, etc. Curing some old, hardened rubber isolators there will help a lot too.

 

[dace voit]

B - Bleed: Flush out the old AHC fluid

1. Procure three 1L bottles of OEM AHC fluid (08886-81221)
2. Put AHC in Low, turn engine off
3. Suck all old fluid out of AHC tank (~1L if level was between Max/Min at N height)
4. Pour in new fluid to top of tank (~2.5L)
5. Bleed accumulator until fluid stops (long cylinder on left side frame rail) (~300mL, 10mm wrench)
   • Bleeder torque spec: 62 in-lbf (5.5 ft-lbf, 7.5 N-m)
6. Bleed one front and one rear damper (globe unit) until both front and rear are on the bump stops and fluid stops flowing (~300-400mL each)
   • Bleeder torque spec: 73 in-lbf (6.0 ft-lbf, 8.1 N-m)
   • Careful, as the car will lower significantly during this process. Don't put yourself under the vehicle!
7. Start car, put AHC in Neutral until pump stops, turn off again
8. Bleed the remaining front and rear dampers on the other side of the car for just a second until fresh fluid and no air comes out (~50mL each)
9. Start car, cycle to AHC to L then back to N
10. Top off AHC fluid in the reservoir. Should be between Max/Min at N height.
11. Recheck graduations in the tank as described in step A2. May see some improvement, may not.

So just to make sure here, Bleed the left 3 components in "L" and the right 2 in "N" position? Seems like leaving the system in L would not allow new fluid to get to the 3 components on the left side whereas raising the system to N would pull fresh into the system? Am I missing something here?