Intro & AHC Question

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Intro
Hey folks. Long time lurker and recent purchaser of an '03 LX 470 in great condition. Rides incredibly well, handles well, and powertrain is in fantastic shape (surprise?). I can actually still pull 17 MPG on the interstate...no cruise control, of course. :^) As far as the dealer knew, this had been Lexus serviced for most of its life.​
My TODO list for mods:​
  1. Plasti-Dipping the chrome on the grill and tailgate to gun-metal gray. If my wife says the chrome is too flashy for me....I guess I'll have to take a look at it ;^)
  2. VHF/UHF HAM radio setup
  3. Better Tires
  4. Roof Tent?? We rock climb, hike, and camp a lot.
  5. New bumpers
  6. Rockets
I've pasted some glam shots below.​

AHC QUESTION:

Everything on this rig has worked as expected, but it has developed a finicky AHC since I purchased. At time of sale, the dealer told me that the AHC system had been "disabled". I got under the truck and the globes were all still there and all the system was still in place, but pressing the height control buttons made no change. I eyeballed the fluid in the reservoir and there was next to nil. Thus I assumed it was in fact disabled.​
About a month after purchase, the front end would occasionally lower when shutting off the truck. When I cranked it again, the front end would raise back up to the neutral ride height and it would still not respond to pressing the raise and lower buttons.​
Fast forward to yesterday evening (2.5 months of ownership) and my wife came to pick me up in it. She parked the car and the front end lowered (engine still running). I took a video of the following: I had her raise the truck to the highest setting, drop to lowest setting, return to neutral, and do that all over 3 times in a row. It worked perfectly -- had never had it work before and haven't since. Drove it back home, and it no longer responded to pushing the ride height buttons. I guess she has the magic touch.​
I took another look at the AHC fluid reservoir tonight and it is only filled up to approx. the second notch on the reservoir. Almost none but still more than expected for a "disabled" system. Do you all recommend I pick up a bottle of AHC fluid and give it a shot? I'd rather have the full AHC system working if the hyraulics are all still in place. Otherwise I'd remove the AHC entirely and replace it with coils and shocks, but don't want to spend those $$$ right now if I can pick up a $35 bottle of AHC fluid.​

Thanks for any help.
- G

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I took another look at the AHC fluid reservoir tonight and it is only filled up to approx. the second notch on the reservoir. Almost none but still more than expected for a "disabled" system. Do you all recommend I pick up a bottle of AHC fluid and give it a shot? I'd rather have the full AHC system working if the hyraulics are all still in place. Otherwise I'd remove the AHC entirely and replace it with coils and shocks, but don't want to spend those $$$ right now if I can pick up a $35 bottle of AHC fluid.​

Might be worth a shot, but I’d spend the $35 on a techstream cable and do a better diagnosis
 
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Yup, that’s how I got TechStream up and running on my ‘03 LX.
Update on this, I used a buddy's scanner today and it reported no codes on the whole system. Its good and hot out there, and the AHC had no issue raising and lowering, surprisingly...that's at least twice now that it has worked out of the blue. I let the scanner run continuously while raising and lowering and it never reported a code.

So should add AHC replacement fluid and see what happens? I figure one of the globes could have gone bad, which may be why the levels are low...let me know what ya'll think.

Thanks
 
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Well I'm not sure if my situation applies to yours, but figured I'd chime in too.

What you described is similar to when I first bought my 98 LX, the PO said he never used the AHC (pushing the buttons to go high or low) and it was strictly a grocery getter for his family with two young kids. Sure enough, when I met up with him to go over the car, it didn't work. Everything was there, he was surprised it didn't work but he never really bothered with it. I offered him a lower price because I wasn't planning to remove the AHC or fix it. He accepted and that was that.

A few days later, after pressing the buttons, it would randomly lower when set to Lo, and I scratched my head because I didn't understand the system. Then one day I was messing with the heated seats buttons and found that they were super sticky. I decided to pop out the buttons and discovered old soda residue and cleaned it all off. Then it clicked to me that maybe my issue wasn't the system, maybe it was the actual button/controls. So I popped out the AHC/Suspension setting button/switch assembly and discovered a ton of soda residue. I cleaned it off and the AHC would work more often but not all the time, so a quick search on eBay, and I found a used button assembly for around $35. I swapped parts and BAM, has worked ever since.

Anyways, I would just check the button/switch to make sure that isn't the issue. An easy way to check is to swap it out with someone else that has a working AHC system. Good luck!
 

suprarx7nut

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Get yourself techstream and a cable. Get yourself a bottle or two of AHC fluid.

Boggles my mind how many AHC vehicles are sitting "disabled" or had the system removed for minor things.

If it goes up and down and doesn't feel completely broken like a no-suspension tractor you're probably only <$500-1000 away from a perfectly functional hydraulic suspension.
 
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Is the ride stiff? Those globes are a worn item. I would replace all 4 globes and go through that process.

There is not a single suspension that feels as good as a functioning AHC system.
More updates from today: I started it after work and the system worked again, almost flawlessly, even with low fluid.
  1. Rasied and lowered correctly
  2. Took off after raising to highest setting and it lowered itself at 10-15 MPH as expected
Only problem with it was that if I lowered it to the low setting and started driving, it would raise back up to neutral. Is that expected behavior? I'd like to lower it on the interstate if the functionality is there.

The techstream still reported no error codes when running the system, and while driving.

As for the ride, its been too comfortable so far, more like a Grand Marquis ride. I had never tried changing the "ride quality" dial (goes from soft to hard) and gave it a stab on a particularly bumpy road today....and I'll be darn, that worked too. No more sloshing around like I'm a bass stuck in a fish tank, it stiffened up and handled very well.

So my only question now is why does the LX raise up from the lowest height setting when I start driving? Maybe that's the low AHC fluid.
 
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Well I'm not sure if my situation applies to yours, but figured I'd chime in too.

What you described is similar to when I first bought my 98 LX, the PO said he never used the AHC (pushing the buttons to go high or low) and it was strictly a grocery getter for his family with two young kids. Sure enough, when I met up with him to go over the car, it didn't work. Everything was there, he was surprised it didn't work but he never really bothered with it. I offered him a lower price because I wasn't planning to remove the AHC or fix it. He accepted and that was that.

A few days later, after pressing the buttons, it would randomly lower when set to Lo, and I scratched my head because I didn't understand the system. Then one day I was messing with the heated seats buttons and found that they were super sticky. I decided to pop out the buttons and discovered old soda residue and cleaned it all off. Then it clicked to me that maybe my issue wasn't the system, maybe it was the actual button/controls. So I popped out the AHC/Suspension setting button/switch assembly and discovered a ton of soda residue. I cleaned it off and the AHC would work more often but not all the time, so a quick search on eBay, and I found a used button assembly for around $35. I swapped parts and BAM, has worked ever since.

Anyways, I would just check the button/switch to make sure that isn't the issue. An easy way to check is to swap it out with someone else that has a working AHC system. Good luck!
Hah! Coca-Cola will do that to you. Yeah, I'd wondered if it was the buttons but they seem to be triggering the electronics just fine -- i.e. the height setting under the speedometer always responds to pushing the buttons. And apparently after today the ride quality dial works as well.

I don't know why it didn't work for two months then suddenly came to life, but its okay with me. Though I will swap the AHC for shocks and coils eventually
 
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It raises to N after hitting 12-13MPH, that's expected. You don't want to drive around in Low or High, it's not what the suspension was designed for.

Start with this thread The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/

And you probably want to exchange the AHC fluid see here Props to PADDO's AHC fluid replacement method! - https://forum.ih8mud.com/threads/props-to-paddos-ahc-fluid-replacement-method.925459/
 
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It raises to N after hitting 12-13MPH, that's expected. You don't want to drive around in Low or High, it's not what the suspension was designed for.

Start with this thread The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/

And you probably want to exchange the AHC fluid see here Props to PADDO's AHC fluid replacement method! - https://forum.ih8mud.com/threads/props-to-paddos-ahc-fluid-replacement-method.925459/
Yes, I knew it wasn't designed to run at highway speeds on the high ride height setting. But thought there would be an aerodynamic advantage to being able to run it at the low height on highway speeds.

And thanks for the reminder....a flush may be in order soon.
 
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I got the replacement AHC fluid in the mail last week. Filled it up to the fill line and everything is working correctly, even the ride control (soft to hard suspension). I'm keeping my eye on the garage floor for any obvious leaks that would have bled the system to the low AHC fluid level it was at when I bought it. Otherwise I assume it could be that one of the globes went bad.

Thanks to all for the help.
 
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Glad you resolved the issue.

I am a recent owner of an 04 470 and at first i wasn't sure about how I felt about the AHC. The thing felt so floaty to drive at speed, I switched things over to SPORT in the firmest setting and it's definitely more drivable now. I also took it off road over the weekend and even with street tires this thing felt SO much smoother than my friend's GX470 that has OME stuff installed. Maybe it's the longer wheelbase but I swear the 470 drove much smoother over the baby heads. I'm sold on this system and plan to keep it for as long as it's feasible.
 
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I got the replacement AHC fluid in the mail last week. Filled it up to the fill line and everything is working correctly, even the ride control (soft to hard suspension). I'm keeping my eye on the garage floor for any obvious leaks that would have bled the system to the low AHC fluid level it was at when I bought it. Otherwise I assume it could be that one of the globes went bad.

Thanks to all for the help.
Looks like a good beginning has been made and the AHC/TEMS systems on this truck could easily be brought back to excellent condition. Unless the vehicle underside is overwhelmed by rust, AHC maintenance and replacement of some AHC components would be quicker, less expensive and give a better ride than replacement with a conventional suspension.

If not already seen, the General Description of the AHC system and TEMS system is a worthwhile read to get an understanding of how these systems work – 20 page description with good diagrams, comes from the official Toyota LC100 Factory Service Manual (FSM) – but AHC/TEMS are exactly the same in LX470. Explanations are also included about how these systems work under various load conditions and speed conditions. See
https://lc100e.github.io/manual/,
then tabs at the Index Panel
New Car Features > CHASSIS > Suspension > Active Height Control Suspension and Skyhook TEMS

In the situation described in this thread, it is likely that there is air in the system if the AHC Tank has become empty or close to empty at some stage. Best to do several ‘bleed’ cycles to be confident that all air is purged. Air in the system will cause a spongy, springy kind of ride.

In a 2003 (18 years old) vehicle,
  • if there is no record of change-out of ‘globes’ (called ‘Gas Chambers’ in FSM), and,
  • low fluid level in the tank is observed,
then it is a fair bet that the ‘globes’ are well past their best, meaning,
  • the ‘globes’ have progressively lost some or all of their nitrogen – this is inevitable with long age/miles,
  • AHC fluid progressively takes up more space (volume) permanently in the four ‘globes’ – which means fluid level progressively drops in AHC tank over time.
This is easily checked – just observe AHC Fluid level in the AHC tank when suspension is in “LO” and observe again when suspension is in “HI”. When ‘globes’ are new, difference in graduations on the tank between “LO” and “HI” is around 14. When this difference is around 7 graduations, it is time to change ‘globes’. This is the basic test used to check overall condition of the 'globes'. It only is accurate when Front and Rear AHC pressures are in the correct ranges specified in the FSM – but doing it any time gives a rough idea.

Note: ‘Globes’ in poor condition will not be revealed by any Diagnostic Trouble Code (DTC) on any scanner. Nor will air in the system be revealed by a DTC, unless the situation is so bad that it has affected the operation of the AHC Pump.

It is possible that only one ‘globe’ has a problem as you mention – but that would be unusual. It is much more likely that all four ‘globes’ have declined, as they are all of similar age/miles.

Be aware that the ability of the AHC system to raise and lower the vehicle tells nothing about the condition of the ‘globes’. The system will do this when the ‘globes’ are new or when the ‘globes’ are dead (unless there is some other different problem). Raise/Lower is the effect of the Height Control Accumulator and the AHC Pump adding pressure and fluid to the ‘shock absorbers’ which act like hydraulic struts to raise the vehicle, or, the effect of the Gate Valves in the Control Valve Assembly releasing pressure and fluid from the 'shock absorbers' back to the AHC Tank to lower the vehicle. Raise/Lower has nothing to do with the ‘globes’ and tells nothing about 'globe' condition.

In a 2003 (18 years old) vehicle, it is inevitable that Front and Rear AHC pressures are higher that FSM-specified ranges unless pressures have been measured periodically and maintenance actions taken. High (or low) pressures will reduce damping performance and affect ride quality. Over-pressures also will eventually challenge valves and seals in the system, especially at the ‘shock absorbers’. AHC over-pressures are a consequence of excess load carried by the AHC system rather than the Front torsion bars and the rear coil springs. Testing of AHC pressures using Techstream or other suitable scanner is essential. However, be aware that AHC pressures by themselves tell nothing about the condition of the ‘globes’ -- the test mentioned above is essential for that purpose.
 
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