The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (2 Viewers)

[Rotheeno]

After 2 days fighting to connect TS to the car, I got from here:

To here:

Healthy numbers I'd say. Except for the rear pressure sensor, so I'll order new springs soon.
Very happy with the ride quality now, but still to be improved

 

[trdcorolla]

After 2 days fighting to connect TS to the car, I got from here:
View attachment 2842206

To here:
View attachment 2842205

Healthy numbers I'd say. Except for the rear pressure sensor, so I'll order new springs soon.
Very happy with the ride quality now, but still to be improved

My rear pressure drops almost 1.0 when I unplug the AHC temp sensor (unplugging the sensor to get the rear pressure is in the FSM from what i've read here on mud).

 

[Catmandrew]

I may have made a boo-boo and I'm seeking advice! I followed an erroneous YouTube tutorial on an AHC flush and cracked the accumulator bleeder while in HI after the initial bleed on N and a pump up. I got very high pressure foamy fluid come out and blow off my bleeder hose (not the kinda hose blow off I was looking for...) Now it seems all bleeders emit foamy fluid and I'm wondering if I damaged my globes or if the membranes were already damaged. Vehicle is a 2000 lx with 200k miles. I don't think the AHC button had ever been pushed before but seemed to work fine, just low on fluid and dark/dirty. I'm waiting for more fluid to show up at the dealer before I do any more bleeding.

 

[suprarx7nut]

I may have made a boo-boo and I'm seeking advice! I followed an erroneous YouTube tutorial on an AHC flush and cracked the accumulator bleeder while in HI after the initial bleed on N and a pump up. I got very high pressure foamy fluid come out and blow off my bleeder hose (not the kinda hose blow off I was looking for...) Now it seems all bleeders emit foamy fluid and I'm wondering if I damaged my globes or if the membranes were already damaged. Vehicle is a 2000 lx with 200k miles. I don't think the AHC button had ever been pushed before but seemed to work fine, just low on fluid and dark/dirty. I'm waiting for more fluid to show up at the dealer before I do any more bleeding.

You got gas/air in the system. Question is whether that was nitrogen from a dead globe or from letting the reservoir run dry.

Either way, you have a lot of bleeding ahead of you.

 

[Catmandrew]

You got gas/air in the system. Question is whether that was nitrogen from a dead globe or from letting the reservoir run dry.

Either way, you have a lot of bleeding ahead of you.

The reservoir was still full at that point so I'm guessing globes.

 

[suprarx7nut]

The reservoir was still full at that point so I'm guessing globes.

Yup. I bet you'll see far more bubbles at the corner(s) that have the dead globe (s).

 

[Catmandrew]

Yup. I bet you'll see far more bubbles at the corner(s) that have the dead globe (s).

Seemed like all of them at the time. That was last week.

 

[IndroCruise]

I may have made a boo-boo and I'm seeking advice! I followed an erroneous YouTube tutorial on an AHC flush and cracked the accumulator bleeder while in HI after the initial bleed on N and a pump up. I got very high pressure foamy fluid come out and blow off my bleeder hose (not the kinda hose blow off I was looking for...) Now it seems all bleeders emit foamy fluid and I'm wondering if I damaged my globes or if the membranes were already damaged. Vehicle is a 2000 lx with 200k miles. I don't think the AHC button had ever been pushed before but seemed to work fine, just low on fluid and dark/dirty. I'm waiting for more fluid to show up at the dealer before I do any more bleeding.

No -- you have not damaged anything nor done anything particularly wrong. It just means that probably you have filled the Height Control Accumulator after raising the vehicle and then emptied the Accumulator by opening its bleeder valve. The only damage is the mess that is made if the discharge hose comes off the bleeder.

Your description of bubbles everywhere when bleeding means either that there is air throughout the system OR that one or more 'globe' membranes are failing and leaking nitrogen which is now throughout the system. As @suprarx7nut mentions, if ‘globes’ are failing, bubbles will be most obvious at the failed ‘globe(s)’. Would all four ‘globes’ fail together? Maybe yes, maybe no. Think about other wear items like conventional shock absorbers, tyres, brake pads, etc – when one is worn the others usually are not far behind. [Note: AHC 'shock absorbers' are way different to conventional shock absorbers, really are just hydraulic struts, and usually only fail when prolonged excessive AHC pressures overwhelms internal seals or when rust destroys them].

When the vehicle is lowered (and when the self-levelling function operates) AHC fluid moves from the ‘shock absorbers’ and the ‘globes’ back to the AHC Tank. So if the ‘globes’ are failing, ‘bubbly’ fluid arrives at the AHC tank and sometimes it can be observed there before the ‘bubbles’ eventually escape to atmosphere.

When raising LO to N or when raising N to HI, the solenoid valve opens at the front of the Height Control Accumulator which then discharges its fluid volume and pressure to the ‘shock absorbers’ to lift the vehicle. The AHC Pump then recharges the Height Control Accumulator. [Theoretically this takes around 15 seconds after raise completed for a new stock vehicle but practically allow 30 to 60 seconds for an old, heavy vehicle].

If the AHC Fluid in the tank contains entrained or dissolved gas or air, then that is sent by the AHC Pump to the Height Control Accumulator during recharge, and then when the Height Control Accumulator next operates, this polluted fluid is sent on to the ‘shock absorbers’ and to the fluid side of the ‘globes’.

Or during self-levelling, polluted fluid is sent by the AHC Pump directly to the ‘shock absorbers’ and the ‘globes’.

If the membranes in the ‘globes’ are failing, then more nitrogen leaks through the membrane into the fluid, and the situation progressively deteriorates.

The test of the overall condition of the four ‘globes’ is given in the first attachment. This test is meant to be done with AHC pressures in the FSM-specified range and is not reliable at other pressures. Nevertheless, it gives an idea of overall ‘globe’ condition, although it does not indicate problems with individual 'globes'.

The so-called 16 step test can give an idea of what is happening at each corner. See Pages 5 and 6 of the second attachment -- section 4 Damping Force Controlling Condition Check.

If the 'globes' are original, then after 21 years and 200,000 miles they are a long way past their best and in that case replacement 'globes' are in your near future. Best price for a set of four ‘globes’ at the moment seems to be around USD700 imported from Impex and landed in USA, usually much, much more from most Lexus and Toyota dealers. Suggest check prices for 2 x Front 49141-60010 and 2 X Rear 49151-60010 at IMPEX JAPAN — online new genuine spare parts shop - https://en.impex-jp.com/ and at PartSouq Auto Parts Around the World - https://partsouq.com/ -- see also plenty of posts on IH8MUD experiences with both of these suppliers.

Air can be a culprit, most usually entering the system when the AHC Tank is not kept topped up during the bleeding process and air enters the pump.

The other less frequent cause is air drawn past worn internal pump seals and o-rings. These can be replaced – parts cost only a few dollars. That may also be a wise time to replace the AHC Pump (not the whole assembly, just the pump and the seals – pump 48901-60010 at USD164.94 , seal 90311-10001 at USD4.28, o-ring 90301-06012 at USD2.34, o-ring 90301-70003 at USD2.31 – cross check these Partsouq prices with Impex and others and add delivery charges and cross-check local dealer prices).

If the AHC system is in reasonable shape (not overwhelmed by rusted pipes and fittings or damaged wiring harnesses and connectors), then these repair/replacements are good value if the comfort provided by the adaptive damping of the suspension is desired to be preserved, along with ability to select heights.

Replacing AHC hydraulic components always involves careful full bleeding of the entire system with new AHC Fluid to get rid of the air which has entered during parts replacement, and to purge any remnant nitrogen gas from previously failed 'globes'. Note that multiple bleeding efforts may be required -- the system is not "open" and cannot be fully flushed end-to-end like most brake systems. Air may remain trapped in 'shock absorbers', in long pipes or in the Height Control Accumulator. Persistence sometimes is necessary.

By the way, if you have not seen the third attachment it is worth a careful read, especially those parts which explain the function of individual components and how the AHC/TEMS hydraulic circuits operate in various conditions.

 

[Catmandrew]

No -- you have not damaged anything nor done anything particularly wrong. It just means that probably you have filled the Height Control Accumulator after raising the vehicle and then emptied the Accumulator by opening its bleeder valve. The only damage is the mess that is made if the discharge hose comes off the bleeder.

Your description of bubbles everywhere when bleeding means either that there is air throughout the system OR that one or more 'globe' membranes are failing and leaking nitrogen which is now throughout the system. As @suprarx7nut mentions, if ‘globes’ are failing, bubbles will be most obvious at the failed ‘globe(s)’. Would all four ‘globes’ fail together? Maybe yes, maybe no. Think about other wear items like conventional shock absorbers, tyres, brake pads, etc – when one is worn the others usually are not far behind. [Note: AHC 'shock absorbers' are way different to conventional shock absorbers, really are just hydraulic struts, and usually only fail when prolonged excessive AHC pressures overwhelms internal seals or when rust destroys them].

When the vehicle is lowered (and when the self-levelling function operates) AHC fluid moves from the ‘shock absorbers’ and the ‘globes’ back to the AHC Tank. So if the ‘globes’ are failing, ‘bubbly’ fluid arrives at the AHC tank and sometimes it can be observed there before the ‘bubbles’ eventually escape to atmosphere.

When raising LO to N or when raising N to HI, the solenoid valve opens at the front Height Control Accumulator which then discharges its fluid volume and pressure to the ‘shock absorbers’ to lift the vehicle. The AHC Pump then recharges the Height Control Accumulator. [Theoretically this takes around 15 seconds after raise completed for a new stock vehicle but practically allow 30 to 60 seconds for an old, heavy vehicle].

If the AHC Fluid in the tank contains entrained or dissolved gas or air, then that is sent by the AHC Pump to the Height Control Accumulator during recharge, and then when the Height Control Accumulator next operates, this polluted fluid is sent on to the ‘shock absorbers’ and to the fluid side of the ‘globes’.

Or during self-levelling, polluted fluid is sent by the AHC Pump directly to the ‘shock absorbers’ and the ‘globes’.

If the membranes in the ‘globes’ are failing, then more nitrogen leaks through the membrane into the fluid, and the situation progressively deteriorates.

The test of the overall condition of the four ‘globes’ is given in the first attachment. This test is meant to be done with AHC pressures in the FSM-specified range and is not reliable at other pressures. Nevertheless, it gives an idea of overall ‘globe’ condition, although it does not indicate problems with individual 'globes'.

The so-called 16 step test can give an idea of what is happening at each corner. See Pages 5 and 6 of the second attachment -- section 4 Damping Force Controlling Condition Check.

If the 'globes' are original, then after 21 years and 200,000 miles they are a long way past their best and in that case replacement 'globes' are in your near future. Best price for a set of four ‘globes’ at the moment seems to be around USD700 imported from Impex and landed in USA, usually much, much more from most Lexus and Toyota dealers. Suggest check prices for 2 x Front 49141-60010 and 2 X Rear 49151-60010 at IMPEX JAPAN — online new genuine spare parts shop - https://en.impex-jp.com/ and at PartSouq Auto Parts Around the World - https://partsouq.com/ -- see also plenty of posts on IH8MUD experiences with both of these suppliers.

Air can be a culprit, most usually entering the system when the AHC Tank is not kept topped up during the bleeding process and air enters the pump.

The other less frequent cause is air drawn past worn internal pump seals and o-rings. These can be replaced – parts cost only a few dollars. That may also be a wise time to replace the AHC Pump (not the whole assembly, just the pump and the seals – pump 48901-60010 at USD164.94 , seal 90311-10001 at USD4.28, o-ring 90301-06012 at USD2.34, o-ring 90301-70003 at USD2.31 – cross check these Partsouq prices with Impex and others and add delivery charges and cross-check local dealer prices).

If the AHC system is in reasonable shape (not overwhelmed by rusted pipes and fittings or damaged wiring harnesses and connectors), then these repair/replacements are good value if the comfort provided by the adaptive damping of the suspension is desired to be preserved, along with ability to select heights.

Replacing AHC hydraulic components always involves careful full bleeding of the entire system with new AHC Fluid to get rid of the air which has entered during parts replacement, and to purge any remnant nitrogen gas from previously failed 'globes'. Note that multiple bleeding efforts may be required -- the system is not "open" and cannot be fully flushed end-to-end like most brake systems. Air may remain trapped in 'shock absorbers', in long pipes or in the Height Control Accumulator. Persistence sometimes is necessary.

By the way, if you have not seen the third attachment it is worth a careful read, especially those parts which explain the function of individual components and how the AHC/TEMS hydraulic circuits operate in various conditions.

Thank you so much for this detailed analysis! I think globes are probably in my near future so I will be sure to read up in their replacement. This vehicle has lived its entire life with the previous owner in the bay area and everything is in excellent condition otherwise with almost no rust present.

 

[Muhammad Rais]

Today morning all of a sudden my rig dropped to low on my way to work. Came back and took this screenshot. Seems like no pressure on the accumulator. What should I try?

 

[2001LC]

Look for leak

 

[Muhammad Rais]

Look for leak

I emptied all four sides now there is fluid inside the globes or accumulator anymore. There’s no leak. Also oil is not going down from the reservoir. I filled it up and it stayed the same. I forgot how to do the manual way. I remember last year I push one pin on the diagnostic port and then push low high and it forced to work. Can’t remember. Again there’s no leak under the car.

 

[2001LC]

Did you use 2 or 3 plastic bottles of Toyota AHC fluid?
Did failure happen, Before or after you filled system?

 

[Muhammad Rais]

Did you use 2 or 3 plastic bottles of Toyota AHC fluid?
Did failure happen, Before or after you filled system?

Yes

 

[2001LC]

Yes

Yes? those question need more than just a YES.
How many bottles of Toyota AHC?
Where they the plastic bottles?
Was the failure before or after flushing the system?

 

[Muhammad Rais]

Yes? those question need more than just a YES.
How many bottles of Toyota AHC?
Where they the plastic bottles?
Was the failure before or after flushing the system?

I flushed the system last year. It worked fine all this time. All of a sudden it went down while driving. So I emptied all four corners including accumulator then topped of the reservoir. Even though reservoir was on correct level when it went down. But after I emptied all 4 corners it’s not taking anything from reservoir. It stayed them same level as before. No pressure and there’s no more oil coming from any corners after I opened each valves.

 

[Slickspawn]

I just bought the Toyota 2.5L AHC fluid from eBay but heard there’s a bad batch of it. Anyone watching this thread have any insight? Should I use it or return it? Is it beneficial to strain it first through cheesecloth or something?

 

[Muhammad Rais]

I just bought the Toyota 2.5L AHC fluid from eBay but heard there’s a bad batch of it. Anyone watching this thread have any insight? Should I use it or return it? Is it beneficial to strain it first through cheesecloth or something?

I used plastic small black bottles from Toyota dealership

 

[riffman12]

I just bought the Toyota 2.5L AHC fluid from eBay but heard there’s a bad batch of it. Anyone watching this thread have any insight? Should I use it or return it? Is it beneficial to strain it first through cheesecloth or something?

I have a metal can that I bought from a Toyota dealership. I plan to put it in the car tomorrow so hopefully it's ok?

I believe all the bad batches were taken out of circulation unless you bought it from a private seller or something.

Someone feel free to correct me if I'm wrong

 

[2001LC]

Many of the Toyota AHC fluid in black plastic 1 liter bottles, have been found to have jelled. Seems mid to early 2021 (a lot of reports out of TX), have jelled. It may have to do with plastic reaction with the fluid.

Toyota switched back to the 2.5 liter tin cans, mid to late 2021..