AHC Accumulator Bleed Question (1 Viewer)

[texasterminator]

Before anybody slams me for creating yet another AHC thread, please know that I have searched for weeks and not found anything on this specific issue that I am having.

History:
I have a 2001 LX470 with 299K miles that the dealer replaced the front AHC globes on at 265K (12/05/2017). Around two years ago, I replaced the rear AHC globes at 293K. The vehicle drove smooth for the last 2 years but I now have developed a pogo stick front end. I have flushed the system several times but ride is still harsh. I am getting about 6 graduations on the reservoir from L to H, which I think means the globes are likely bad.

Pressures:
Front = 6.4MPa
Rear = 6.1 MPa

Issues:
1. Poor ride quality in front only.
2. When flushing and bleeding, I am getting nice fluid out of each globe actuator but the accumulator continues to have air and poor fluid appearance (grey). Also, when bleeding the accumulator, I start to see some very small rubber diaphragm debris from the old globes (I assume) followed by an abrupt stop of fluid evacuation.

Questions:
1. Is it likely that the front globes need to be replaced again?
2a. Is it normal to have the accumulator just stop flowing or should it continue to drain the reservoir?
2b. Could this cause dampening issues in the front only?

I have ordered new front globes from Cruiser Parts but I hope I don't need them...

 

[IndroCruise]

Before anybody slams me for creating yet another AHC thread, please know that I have searched for weeks and not found anything on this specific issue that I am having.

History:
I have a 2001 LX470 with 299K miles that the dealer replaced the front AHC globes on at 265K (12/05/2017). Around two years ago, I replaced the rear AHC globes at 293K. The vehicle drove smooth for the last 2 years but I now have developed a pogo stick front end. I have flushed the system several times but ride is still harsh. I am getting about 6 graduations on the reservoir from L to H, which I think means the globes are likely bad.

Pressures:
Front = 6.4MPa
Rear = 6.1 MPa

Issues:
1. Poor ride quality in front only.
2. When flushing and bleeding, I am getting nice fluid out of each globe actuator but the accumulator continues to have air and poor fluid appearance (grey). Also, when bleeding the accumulator, I start to see some very small rubber diaphragm debris from the old globes (I assume) followed by an abrupt stop of fluid evacuation.

Questions:
1. Is it likely that the front globes need to be replaced again?
2a. Is it normal to have the accumulator just stop flowing or should it continue to drain the reservoir?
2b. Could this cause dampening issues in the front only?

I have ordered new front globes from Cruiser Parts but I hope I don't need them...

There is no problem creating "yet another AHC thread" -- just ask away!

There is not enough information to offer a definitive diagnosis but here are a few thought-starters which may help ….

Vehicle:
2001 LX470 -- so 22 years old
299,000 miles
DFW Texas vehicle -- so underbody probably is in good condition???
Build/Loading/Weight -- not stated (near stock or heavy build?)
Height of vehicle (hub to fender) -- not stated (near stock 19.75” Front, 20.50” Rear – or incorrect, or lifted??)
Height Control Sensor Readings -- not stated -- at “N”, all near zero +/- 0.2”??
Age of Height Control Sensors -- not stated -- original and 22 years old??
265,000 miles -- new OEM Front ‘globes’ in May 2017 (5 years ago)
293,000 miles -- new OEM Rear ‘globes’ in ~2020

Pressures:
Front = 6.4MPa
Rear = 6.1 MPa

Volume change between and “HI” and “LO”:
~6 graduations at the AHC Tank – poor result

Symptoms:
Sudden springy (pogo) front end -- means damping is poor
Height Control Accumulator repetitively drains air and debris, flow stops abruptly

Answers:

1. Is it likely that the front globes need to be replaced again?

• Possible -- but seems highly unlikely -- noting four ‘globes’ were new OEM fitted in 2017/2020,
• Possible that a membrane in a ‘globe’ has collapsed -- but seems highly unlikely,
• Suspect different cause of poor HI/LO reading (which measures the overall effect of all four globes).
• For example, does vehicle reach correct height when moving from “LO” to “N” and “N” to “HI”?? Or is the raise incomplete??
• If the raise is incomplete, then the HI/LO reading cannot be accurate or reliable,
• The HI/LO Test assumes that fluid displacement from the ‘shock absorbers’ is always correct, meaning that the ‘shock absorber stroke’ between “HI” and “LO” does not does not change over time because it is set within the Suspension Electronic Control Unit (ECU). In an otherwise healthy AHC system at FSM-specified AHC pressures the observed decline in graduations at the AHC Tank over the time (years) then is due solely to steadily declining ‘globes’ pushing less AHC Fluid back to the Tank -- in turn due to lost nitrogen and diminished gas pressures behind the membranes in aging ‘globes’.
• hub-to-fender physical tape-measurements AND Height Control Sensor readings are basic data -- both kinds of data are essential to any AHC/TEMS diagnosis,
• there can be multiple causes of an incomplete raise, such as:
  • overweight vehicle -- too heavy to complete the raise,
  • air (or nitrogen) in the system and the pressure developed by the AHC Pump is expended in compressing gas,
  • poor AHC Pump condition after 22 years of service and/or partially blocked strainers within the AHC Pump sub-assembly (not the strainer at the AHC Tank) -- it is not difficult to disassemble and clean the AHC Pump but after 22 years the smarter move is to replace the AHC Pump sub-assembly 48901-60010,
  • one or more Height Control Sensors in poor condition, have given their best for 22 years and 299,000 miles but are now worn or defective and due for testing per FSM and most likely retirement, replace ONLY with Toyota/Lexus or AISIN parts and not any of the cheap fakes if further grief is to be avoided.
  • [Special Note: As explained often in other posts, absence of Height Control Sensor DTC’s DOES NOT provide assurance that these Sensors are healthy, actual testing per FSM is necessary],
  • connector and harness faults also detract from the reliability of signals from Sensors to ECU and easily can cause a raise not to completing properly. There are many connector and harness possibilities – the connector BI1 located behind the LHS Rear wheel high up on the inside of the LHS Rear quarter panel is becoming a more common fault on older vehicles.

2a. Is it normal to have the accumulator just stop flowing or should it continue to drain the reservoir?

• Not normal.
• If the Height Control Accumulator has been filled properly by the AHC Pump after a completed raise, then expect ~300 millilitres (about 0.6 pints) to come out when bleeding.
• Also be aware of correct operation of the Height Control Accumulator solenoid – if in doubt, check using Techstream or test electrically per FSM method.
• Finally, be aware of the attached TSB CP-3006 concerning pre-November 2002 Height Control Accumulators.
• Unless there has been a membrane collapse in a ‘globe’ releasing nitrogen (unlikely), then it is a clear that either
  • (a) air has been there for a long time, for example in the Height Control Accumulator, or, deep in the ‘shock absorbers’ which are never truly flushed, and the air eventually works its way back through the system -- in which case, the response is bleed, bleed, bleed -- persistently and multiple times, or,
  • (b) new air is being ingested into the system, via a weak point which after 22 years may be the seal between the AHC Tank and the Pump, or the seal between the AHC Pump and its Motor, or via the large O-ring at the outer cover of the Pump assembly, especially if the AHC Pump is starved for fluid due to a partially blocked inlet strainer within Pump. Then air sucked in, causing aeration and maybe noisy cavitation -- and the ingested air will be pumped around the system and especially to the Height Control Accumulator at the end of a raise cycle. At the next raise operation this polluted fluid will be sent from the Height Control Accumulator all around the system – necessitating renewal of seals and very persistent repetitive bleeding.

2b. Could this cause dampening issues in the front only?

• No.
• The Height Control Accumulator plays no role in damping at any time. Its sole purpose is to speed up the raising of the vehicle.
• If not the causes in the above list, then the next item in the hierarchy would be a fault at one of the four Damping Force Control Actuators to which the ‘globes’ are attached – especially at the Front if that is where springy, undamped behaviour is being experienced.
• Have someone else drive the vehicle with Techstream connected while you observe the variations on Techstream for “Front Wheel Step” and “Rear Wheel Step” and also experiment with the “Comfort” switch on the centre console and observe “Damping Switch 1” and “Damping Switch 2” – if there are no variations, either the AHC system is in ‘fail safe mode’ (no AHC function and damping remains at Step 8, no variable response to road conditions which would show as changes from Step 1 to Step 16), or, there may be a faulty Damping Force Control Actuator.
• If suspicious about the Damping Force Control Actuators, then use the “Damping Force Controlling Condition Test” (also called the “16 Step Test”) at Section 4 of the attachment to detect whether one corner seems more stiff than the others.
• Also remove the covers and connectors from the Front Damping Force Control Actuators and test electrically per FSM.

 

[texasterminator]

@IndroCruise, thank you so much for your detailed reply.

A quick update that I planned on reporting once I have fully confirmed...

I ordered two front "globes" from CruiserParts.net and but, unfortunately, they sent me 1 front and 1 rear accumulator. I realized this only after replacing the LF accumulator.

The left front accumulator failed the "pencil test" very obviously. I have not pulled the RF but I am assuming that it is in the same condition as the ride is now only harsh on the RF. After replacing the LF, the ride is significantly improved and pogo stick ride is basically gone. I assume this is because I went from having, virtually, no dampening on the front to having some. I have not driven much but will report back here once I confirm the other side is collapsed/ruptured, as well.

Parts should be here any day now.

Btw, vehicle has always changed from L to H and back.

 

[IndroCruise]

@IndroCruise, thank you so much for your detailed reply.

A quick update that I planned on reporting once I have fully confirmed...

I ordered two front "globes" from CruiserParts.net and but, unfortunately, they sent me 1 front and 1 rear accumulator. I realized this only after replacing the LF accumulator.

The left front accumulator failed the "pencil test" very obviously. I have not pulled the RF but I am assuming that it is in the same condition as the ride is now only harsh on the RF. After replacing the LF, the ride is significantly improved and pogo stick ride is basically gone. I assume this is because I went from having, virtually, no dampening on the front to having some. I have not driven much but will report back here once I confirm the other side is collapsed/ruptured, as well.

Parts should be here any day now.

Btw, vehicle has always changed from L to H and back.

Amazing short life from the previous replacement 'globes'! Were they new when installed?

Makes sense that there is some improvement when one new 'globe' is added. The Front 'globes' and actuators are hydraulicly connected -- the Front Gate Valve in the Control Valve Assembly is 'normally open' except when the vehicle is turning at speed. Ditto Rear 'globes', actuators and Gate Valve.

 

[texasterminator]

@IndroCruise, yes they were new I would assume since they were installed at the dealership according to the service history.

 

[suprarx7nut]

@IndroCruise, yes they were new I would assume since they were installed at the dealership according to the service history.

That's pretty crazy. Post up some pics of those bad ones. That's usually a 10 year part. Two failing immediately is a really bizarre thing.

 

[texasterminator]

That's pretty crazy. Post up some pics of those bad ones. That's usually a 10 year part. Two failing immediately is a really bizarre thing.

will do

 

[IndroCruise]

Btw, vehicle has always changed from L to H and back.

Just to mention that this response by the vehicle means that it is not in one of the 'fail safe functions' (phew!!) because AHC is at least working.

It is still important to check that the AHC system is working correctly and that a raise has been completed correctly -- even if no DTC's are recorded on Techstream or other scanner. The fact that the raise stops and the AHC Pump stops and the green AHC light on the instrument panel stops flashing does not tell you that the raise has completed correctly.

It is essential to check hub-to-fender physical tape-measurements AND Height Control Sensor readings -- this is basic data. Results should include all Height Control Sensor readings on Techstream near zero +/- 0.2 inches AND physical measurements similar to below:

The attachment to Post #11 at the following link shows what can happen:

AHC Time LO to N, N to HI, LO to HI

I've seen this post by @IndroCruise but I'd like to know what other members experience is on this particular aspect of AHC. Some backstory... I decided that at 207k miles it was time to replace the original globes on my '07 LC. My AHC pressures are well within spec. I got a good deal on globes...

forum.ih8mud.com

In this case most of the relevant components are new and individually they test correctly per FSM on a 'young' 2006 vehicle. There are no DTC's. AHC Pump stops, AHC green light settles at solid green, stops flashing, all as expected after a raise. However, the vehicle has not completed the raise correctly when the hub-to-fender measurements are taken AND the Height Control Sensor readings are observed. Connectors and wiring harness are next on the list in this case.

 

[texasterminator]

Just to mention that this response by the vehicle means that it is not in one of the 'fail safe functions' (phew!!) because AHC is at least working. It is still important to check that the AHC system is working correctly and that a raise has been completed correctly -- even if no DTC's are recorded on Techstream or other scanner. The fact that the raise stops and the AHC Pump stops and the green AHC light on the instrument panel stops flashing does not tell you that the raise has completed correctly. It is essential to check hub-to-fender physical tape-measurements AND Height Control Sensor readings -- this is basic data. Results should include all Height Control Sensor readings on Techstream near zero +/- 0.2 inches AND physical measurements similar to below:

View attachment 3229649
The attachment to Post #11 at the following link shows what can happen:

AHC Time LO to N, N to HI, LO to HI

I've seen this post by @IndroCruise but I'd like to know what other members experience is on this particular aspect of AHC. Some backstory... I decided that at 207k miles it was time to replace the original globes on my '07 LC. My AHC pressures are well within spec. I got a good deal on globes...

forum.ih8mud.com

In this case most of the relevant components are new and individually they test correctly per FSM on a 'young' 2006 vehicle. There are no DTC's. AHC Pump stops, AHC green light settles at solid green, stops flashing, all as expected after a raise. However, the vehicle has not completed the raise correctly when when the hub-to-fender measurements are taken AND the Height Control Sensor readings are observed. Connectors and wiring harness are next on the list in this case.

Thanks again for the information sharing. It's a good point to consider checking after I replace the other globe. I'll report back once that happens.

 

[texasterminator]

I finally received the other accumulator globe and can confidently report back that both front globes, were in fact, failed. The ride is night and day, as expected with failed globes. Gradations are now 13-14 and suspensions seems to be performing as expected. I will run back through all of the specs and double check pressures and measurements later this week.

Thanks for all the support!

 

[IndroCruise]

I finally received the other accumulator globe and can confidently report back that both front globes, were in fact, failed. The ride is night and day, as expected with failed globes. Gradations are now 13-14 and suspensions seems to be performing as expected. I will run back through all of the specs and double check pressures and measurements later this week.

Thanks for all the support!

That is good news!!

Yes -- definitely worth checking and recording all physical tape-measured heights at each wheel and all Height Control Sensor readings, along with Front and Rear AHC pressures and Height Control Accumulator pressure. At the same time, it is worth taking pictures of the condition of the 'shock absorbers' (looking for leaks, 'sweating, rust, etc) and close-ups of the lower shock absorber bushes (looking for cracking, degradation of the rubber) and pictures of hydraulic pipes and tubes and connections (looking for leaks, rust). This gives you a proper base-line for future reference.

The cause of the early demise of the not-very-old 'globes' (2017 or 2020?) remains a puzzle.

It may simply be that the previous 'globes' were not new when installed.

Another possibility may be inadvertent use by a previous owner or by a workshop of incorrect fluid instead of genuine Toyota/Lexus AHC Fluid (or a substitute approved by Toyota/Lexus).

The worst and most disastrous example is the mistaken assumption that brake fluid can be used. Any glycol-based fluid such as brake fluid will cause corrosion and quick failure of the rubber/nitrile/resin compounds used in the multi-layer 'globe' membranes. This may take a while but is inevitable. The hygroscopic (water-loving) nature of glycol-based fluids also risks internal corrosion of valves and pipes in the AHC system.

If any such suspicion exists, then the AHC system should be flushed multiple times with new AHC Fluid.

Hope all goes well and the new 'globes' are long-lasting!!

 

[suprarx7nut]

I finally received the other accumulator globe and can confidently report back that both front globes, were in fact, failed. The ride is night and day, as expected with failed globes. Gradations are now 13-14 and suspensions seems to be performing as expected. I will run back through all of the specs and double check pressures and measurements later this week.

Thanks for all the support!

Awesome! And strange! So those globes were just a few years old? Do they look exactly like the new OEM ones you got?

 

[2001LC]

Couple of thoughts on new-ish globes failing:

Killer of globes is excessive pressure on them. With fronts this can happen with improper T-bar adjustment. Which can be from neglect, mostly to LF globe. Or sensor lift and or extra weight in front end and not compensated.

It's also possible old stock used when replaced. All globes have a date codes. What date are on your bad ones?
Read as 2000 July 3rd at 2:26:12PM

Additionally: it is best driving practice, to dial to AHC Comfort, when on bumpy roads/terrain. In sport mode, the globes, shock & shock bushings take a beating.

Wrong fluid used, perhaps! I have one front shocks (rears not tried) are supper stiff when working in and out by hand off the vehicle. It had a blown out FR globe.

 

[IndroCruise]

Couple of thoughts on new-ish globes failing:

Killer of globes is excessive pressure on them. With fronts this can happen with improper T-bar adjustment. Which can be from neglect, mostly to LF globe. Or sensor lift and or extra weight in front end and not compensated.

It's also possible old stock used when replaced. All globes have a date codes. What date are on your bad ones?

View attachment 3233940

Additionally: it is best driving practice, to dial to AHC Comfort, when on bumpy roads/terrain. In sport mode, the globes, shock & shock bushings take a beating.

Wrong fluid used, perhaps! I have one front shocks (rears not tried) are supper stiff when working in and out by hand off the vehicle. It had a blown out FR globe.

This makes good sense @2001LC -- as always.

An expanded explanation and pictures are offered below and may be of interest to others.

Over-pressure in the hydraulic side of the membrane will be matched by the gas pressure equalising as the nitrogen is compressed on the gas side of the membrane.

With high AHC pressures, flexing of the membrane may be extreme during suspension movements while the vehicle is in motion -- from the “protective button” touching at or near the gas fill-point at the back of the ‘globe’ to touching the AHC Fluid entry point where the ‘globe’ screws into the Damping Force Control Actuator.

The flexing will be worst in rough conditions. In those conditions, the “Comfort” setting adjusts the valve settings within the Damping Force Control Actuator to allow the suspension to move more quickly at bumps by providing less damping force to resist suspension movements. The vehicle (bushes, ‘shock absorbers’, chassis, body and passengers) will feel less shock loadings than at the “Sport” settings where valves are set to increase damping force and provide more resistance to suspension movements.

In this situation, there will be more deeper and faster movements (flexing) of the membrane at the “Comfort” setting, made worse and more violent by excessive AHC Pressures.

Eventually, flexing under increased AHC Pressures will weaken the membrane more quickly than under FSM-specified AHC Pressures. Nitrogen will pass into the AHC Fluid and AHC Fluid will pass to the gas side of the membrane. This may happen slowly or quickly. The ‘damping effect’ provided by the ‘globe’ and Damping Force Control Actuator, acting together, reduces and eventually is lost. A springy (pogo stick) undamped rough ride is then experienced in the vehicle.

So the moral of the story is that long life of AHC ‘globes’, good damping and good ride quality all require that

1. AHC pressures be monitored from time to time -- say yearly or whenever major permanent additions are made to the vehicle, and,
2. AHC pressures be maintained within FSM-specified ranges by adjustment/re-indexing of Front torsion bars and upgrading Rear coil springs to compensate for added permanent loadings.

Just very, very basic maintenance. Easy!