LX470 AHC help/info (1 Viewer)

Joined
Sep 27, 2018
Messages
19
Location
Forsyth, GA
Hi All,

After 4+ years of looking for my very own LC I came across a nice LX470 and pulled the trigger.

It's a 2004 one owner (now retired CPA), GA vehicle with a long list of service at a couple LEXUS dealerships around Atlanta (223K miles) no rust, no accidents, best I can tell everything works.

I was not really planning on purchasing a vehicle with the AHC system, but I figured if they put it on this vehicle and the LC it must be world class, right? Maybe I should give it a chance before I decide to discard it.

So, what are it's strengths & weaknesses?

It goes up. It goes down. It goes in between. Can I adjust the heights of these settings?

I do like it sitting up, like in the high position.

Upon early investigation, it seems that there are other things that I may be able to do to tweak it.

I have read a little about sensors, springs, that sort of thing. Just enough to become lost and confused. Can I replace old springs and shocks?

Someone school me. PLEASE.

I do plan to still buy a LC when the right one comes along, so this one may go to one of the kids one day.

I may do a bumper, sliders, rack, wheels and tires. Not planning on doing anything off road that would risk me not making a 100 or 200 mile trip back home. Just breaking the ice with the off road thing.

Send me your knowledge!

Thanks,
Chris
 
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Joined
Jun 19, 2013
Messages
2,413
Location
Mobile, AL
Enjoy the benefits of the AHC and leave it be until you possibly have issues at some point. Then remember that most everything in life is cheaper to repair than replace.
 

GTV

Joined
Jan 31, 2019
Messages
829
Location
Si'ahl
AHC is fantastic when it's working but it's a complicated system with many potential points of failure. Given the age of these trucks it's not if but rather when it will fail. Normal springs and shocks are stupid simple, cheap and will never leave you stranded.
 

suprarx7nut

The YotaMD Guy
Supporting Vendor
Joined
Sep 28, 2010
Messages
4,004
Location
Colorado
I'm in the pro-AHC camp. It's about as complicated as the brake system. And fails about as often. If you don't worry about the brake booster failing and leaving you stranded I don't think anyone needs to worry about AHC, either. Some basic maintenance and upkeep dramatically reduces the likelihood of failure. Rust would be the major exception to my stance on AHC. If your rig is badly rusted, AHC is far more likely to have annoying/expensive failures. Rust-free rig? Psh, nothing to worry about.

The core components are not complicated and are not very expensive to rebuild/replace, despite internet lore. Fluid flushes every few years and a set of globes for $1,000 every ten years and a pair of rear springs (or spacers) every ten years is about all you need. Roughly the same schedule as normal shocks and only a small bit more complicated.

The marginal increase in maintenance cost pales in comparison to the improved ride on 99.8% of road surfaces you'll encounter. It's a night and day difference.
 
Joined
Dec 6, 2016
Messages
356
Location
Brisbane, Australia
Hi All,

After 4+ years of looking for my very own LC I came across a nice LX470 and pulled the trigger.

It's a 2004 one owner (now retired CPA), GA vehicle with a long list of service at a couple LEXUS dealerships around Atlanta (223K miles) no rust, no accidents, best I can tell everything works.

I was not really planning on purchasing a vehicle with the AHC system, but I figured if they put it on this vehicle and the LC it must be world class, right? Maybe I should give it a chance before I decide to discard it.

So, what are it's strengths & weaknesses?

It goes up. It goes down. It goes in between. Can I adjust the heights of these settings?

I do like it sitting up, like in the high position.

Upon early investigation, it seems that there are other things that I may be able to do to tweak it.

I have read a little about sensors, springs, that sort of thing. Just enough to become lost and confused. Can I replace old springs and shocks?

Someone school me. PLEASE.

I do plan to still buy a LC when the right one comes along, so this one may go to one of the kids one day.

I may do a bumper, sliders, rack, wheels and tires. Not planning on doing anything off road that would risk me not making a 100 or 200 mile trip back home. Just breaking the ice with the off road thing.

Send me your knowledge!

Thanks,
Chris


As a starter and as primer, read the AHC overview document “AHC General Description and Diagrams” so that you get a feel for the nomenclature and how the Active Height Control (AHC) and Toyota Electronic Modulated Suspension (TEMS) actually work in LC100 (where fitted) and LX470. In more recent vehicles, a successor to TEMS is called Adaptive Variable Suspension (AVS).

This document has been posted many times – and I have just now posted it again here at the bottom of a reply.

Then read all of this thread:

Definitive list of AHC maintenance items

This thread is huge unwieldy rambling thing which began in 2012 and now adds up to 811 posts. Some say it is a rite of passage which all have endured, and nobody should be allowed to escape!!!! It is also the ‘keeping place’ of a vast amount of knowledge.

Anyway, start at the beginning and you will soon get the gist of the AHC and TEMS systems and basic diagnoses – and you will quickly identify the early knowledgeable and influential contributors – PADDO, uHu and a host of others. Some of us more recent contributors simply stand on their shoulders and plagiarise relentlessly – or at least that is what I do!

To assist, @tjb helpfully created a PDF collection of this thread up to March 2019.

It is a huge PDF file but downloading is recommended because it is then easily searchable off-line and you can then make up your own list or index of the items most useful to you. This enables easy return later.

For his part, @PabloCruise nominated his favourite “pearls of wisdom” by @PADDO and collected them at this handy post.

Among the early contributors you will also come across @uHu in many different threads– always succinct, wise, to the point and always worth reading on a wide variety of matters.

More recently @LndXrsr set out to produce a concise, orderly summary "The ABCs of AHC" and this thread should be read and watched:

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

There are many, many other contributors and many, many other very informative AHC threads – I intend no offence by failing to name all those whom I have found very helpful and the threads they have produced – but the above links probably are enough material for one weekend :cheers:

It also must be said that the “Search” function on the IH8MUD Site works very, very well – and should be used a lot!

Late edit and apologies: Should have acknowledged and included the Master thread: Buying, PM & Advanced Maintenance of 100 & 200 series prepared by @2000LC .
 
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PabloCruise

SILVER Star
Joined
Jun 3, 2004
Messages
20,837
Location
Northern Colorado
PADDO. Now, that's a name I've not heard in a long time.

sounds like an AHC master of sorts

1596555803042.png
 
Joined
Mar 25, 2020
Messages
130
Location
Nicaragua
Hey guys, quick question:

I am about to get new tires for my rig - 265/70R18s and I was wondering if I have to do anything to the AHC system prior to lifting the truck?

Many thanks
 
Joined
Oct 26, 2019
Messages
1
Location
Houston, TX
Hello All,

This is my first time posting and read alot of other post about AHC issues/fixes and could not find solutions to all my frustration. I seriously need some help with my AHC. The problems I'm encountering are as follows with my assumptions on issue, please let me know if I'm on the
  • Fronts suspension are constantly adjusting upward at every stop light, around every 30 seconds. It seem to adjust down (sometimes) when on the gas. I believe it constantly hunting for the right level. My assumption is the level switch could be bad. I also changed the fluid but did not seem to help. Additionally, the truck seems to ride rough with more vibration when the front height is lower, again, not consistent. sometimes stays in place at normal and sometimes lower.
  • Rear does it every 10 mins.
  • Per Techstream, the AHC pressures are within spec 6.5f/5.6r, but it is not consistent. Sometimes 8.4f/7.3r.
  • The front measurements (with tape) is 22.25", both sides. Note, I installed those spacers. The rear is 23" with Kingsprings and 30mm spacer.
  • Per Techstream, the front driver side measurement is off (higher) by .5 -1". Note, it is set on level ground. No matter what I do to the level switch on driver side it doesn't solve the problem. I also drive it at every incremental adjustment with no luck. My assumptions is that the level switch could be bad.
  • Additional problems, my front and rear does not seem to hold the truck a level normal height over night. It looks to be bottoming out every evening. My assumptions is that the seals at the pump are bad or the globes are getting bad. Note, I changed the globes about 2 years ago which I hope is not the problem.
please advise if you can

Thanks
 
Joined
Dec 6, 2016
Messages
356
Location
Brisbane, Australia
Hello All,

This is my first time posting and read alot of other post about AHC issues/fixes and could not find solutions to all my frustration. I seriously need some help with my AHC. The problems I'm encountering are as follows with my assumptions on issue, please let me know if I'm on the
  • Fronts suspension are constantly adjusting upward at every stop light, around every 30 seconds. It seem to adjust down (sometimes) when on the gas. I believe it constantly hunting for the right level. My assumption is the level switch could be bad. I also changed the fluid but did not seem to help. Additionally, the truck seems to ride rough with more vibration when the front height is lower, again, not consistent. sometimes stays in place at normal and sometimes lower.
  • Rear does it every 10 mins.
  • Per Techstream, the AHC pressures are within spec 6.5f/5.6r, but it is not consistent. Sometimes 8.4f/7.3r.
  • The front measurements (with tape) is 22.25", both sides. Note, I installed those spacers. The rear is 23" with Kingsprings and 30mm spacer.
  • Per Techstream, the front driver side measurement is off (higher) by .5 -1". Note, it is set on level ground. No matter what I do to the level switch on driver side it doesn't solve the problem. I also drive it at every incremental adjustment with no luck. My assumptions is that the level switch could be bad.
  • Additional problems, my front and rear does not seem to hold the truck a level normal height over night. It looks to be bottoming out every evening. My assumptions is that the seals at the pump are bad or the globes are getting bad. Note, I changed the globes about 2 years ago which I hope is not the problem.
please advise if you can

Thanks

Here are a few ideas:

Summary of symptoms reported:

  • Very strange and erratic self-levelling behaviour when driving, squats at lights (presume braking?), dives on gas (presume acceleration?),

  • Erratic AHC pressures – presume when doing Techstream pressures N > L > N, sometimes obtain Front 6.5Mpa and Rear 5.6 Mpa, other times obtain Front 8.4Mpa and Rear 7.3MPa. What are the hub-to-fender heights in each case?? Important to know this as heights and AHC pressures go hand in hand – they are not independent,

  • Hub-to-fender heights tape-measured at Front 22.25 inches both sides, Rear 23.00 inches. Both very high if vehicle is more or less stock (not lifted, tyres do not matter) – should expect Front 19.75 inches, Rear 20.50 inches. Do the actual heights quoted correspond to the high AHC pressures readings quoted??

  • By Techstream, Front Height Control sensor reading differ by 0.5 inches to 1 inches. What are the actual three Height Control Sensor readings?? It is best to add a screenshot of whole page of Techstream output to your posts so all information can be seen at once. (Note: When trying to zero Height Control Sensors, do it as part of the overall AHC check procedure in the correct order: (1) cross level Front Right and Front Left with torsion bar adjusters equal turns in opposite directions (never with Height Control Sensors) per FSM with engine OFF – don’t worry about actual readings, just make them as equal possible, at least within +/- 10 millimetres (0.39 inches, (2) set hub-to-fender heights with Height Control Sensors, (3) adjust Front AHC pressure by winding both torsion bar adjusters in same direction, clockwise to increase load on torsion bars, reduce front AHC pressure or anticlockwise for the reverse effect, (4) lastly, when AHC pressures (and operating heights) are correct, check ‘globe’ condition by measuring changes in levels at AHC tank between LO and HI. Now, with Techstream connected, key “ON”, but engine “OFF” (do not want AHC to activate during adjustment), move Height Control Sensor adjusters as close as possible to zero (within +/- 5 millimetres or 0.2 inches per FSM). [SAFETY NOTE: DO NOT PUT HUMAN BODY UNDER VEHICLE BODY WHEN MAKING SUSPENSION OR AHC ADJUSTMENTS UNLESS VEHICLE STANDS ARE IN PLACE UNDER CHASSIS RAILS TO PREVENT UNINTENDED MOVEMENTS],

  • Vehicle does not hold heights but settles overnight,

  • No Diagnostic Trouble Codes (DTC’s) are reported from Techstream.

Possible causes in order of likelihood (there may be more than one fault):

  • Air in AHC system – it is always worthwhile to consider this possibility. Action: If in doubt eliminate the possibility with further bleeding of the AHC system, using only genuine Toyota/Lexus AHC Fluid,

  • Faulty Height Control Sensors (or linkages or faulty connectors or harness) sending unreliable signals to ECU, certainly causing erratic AHC/TEMS responses, possibly causing the ECU to put AHC into ‘fail safe mode’. Action: Inspect Sensors and harnesses, remove all three Height Control Sensors, open and inspect internally, test per FSM, review IH8MUD experiences, check connectors and harness for continuity and supply voltage, replace Sensors if necessary. [Note: After worn-out ‘globes’, the Height Control Sensors (and/or connectors and harness) probably are the next most common cause of erratic AHC/TEMS symptoms in LC100/LX470 vehicles. These sensors are simple and robust potentiometers which govern the self-levelling height of the vehicle. The sensors and their connectors and harness live under the vehicle in a hostile environment – heat, cold, water, snow, sticks, stones, sand, cause physical damage or water ingress or internal corrosion of Sensor or external corrosion of linkage, or the internal carbon trace or tiny brushes simply become worn, or there has been past incorrect adjustment. Any of these give rise to poor or erratic signals, or signals which are sufficiently different between Sensors to cause erratic AHC/TEMS performance,

  • Faulty Front and/or Rear Solenoid Levelling Valves within the Control Valve Assembly or damage to its connector or harness (all located midway along the inner face of the LHS chassis rail). Action: Inspect condition of connector and its protective shroud and entry of wires to the connector. Check operation of Levelling Valves by sound and touch when vehicle is being raised by AHC system. Remove connector and test solenoid circuits per with multi-meter per FSM. [Note the connector can be quite stiff and difficult to unlock and remove. Clean up first. Study similar five-pin connectors such as the more easily accessible connector to the windscreen wiper motor]. Note that Faulty Control Valve Assemblies are unusual and are rarely reported at IH8MUD. While under the vehicle, it is also worthwhile to check by the operation of the solenoid valve on the Height Control Accumulator (located midway along the outer face of the LHS chassis rail) by sound and touch when the vehicle is being raised by the AHC system, then remove the connector at the rear of the accumulator and test the solenoid circuit with a multimeter per FSM. Consider Height Control Sensors (and connectors and harness) first, before either the Control Valve Assembly or the Height Control Accumulator,

  • Faulty AHC Electronic Control Unit (ECU) -- such faults are rare but happen occasionally, usually accompanied by explicit DTC’s. Consider only if problems persist and after being satisfied with condition and operation of Height Control Sensors and Control Valve Assembly, in that order.

There are other more unusual possibilities but the above items are the recommended starting points.

It is unlikely that the AHC Pump is implicated in the symptoms described.

SAFETY NOTE REPEATED : DO NOT PUT HUMAN BODY UNDER VEHICLE BODY WHEN MAKING SUSPENSION OR AHC ADJUSTMENTS UNLESS VEHICLE STANDS ARE IN PLACE UNDER CHASSIS RAILS TO PREVENT UNINTENDED MOVEMENTS],

Further information:

The following references are recommended for printing and reading (or re-reading) to refresh understanding of how AHC/TEMS are meant to work -- when it they are working properly:

https://lc100e.github.io/manual/: [Note: This link to LC100 FSM applies equally well to LX470 except for specific luxury features].

General Description:

It is worth reading this for general understanding and to help make sure that all are describing the same things in the same way.
Go to tabs at Index Panel, top left of opening page, then -- New Car Features (first item in the list) > CHASSIS > Suspension > Active Height Control Suspension & Skyhook TEMS.

This General Description of the AHC/TEMS system over about 20 pages with many helpful diagrams provides a description of all AHC/TEMS components and what they are meant to do. There are diagrams of the hydraulic circuit on the last 4 pages.

AHC Diagnostics:

At the same link as above, use the Index on the left hand side of the opening page and follow these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS

It is worthwhile to read through this whole section even though it is quite long. Note especially the various forms of ‘fail safe modes’ and the symptoms that accompany them.

Then proceed methodically, looking for possible causes that match your observed symptoms and the various tests which are described in the relevant sub-sections. Obviously, look at the sub-sections which relate to any Diagnostic Trouble Codes (DTC's) appearing on Techstream or other scanner and which cannot be cleared or reappear after clearing. Note that not all faults cause a DTC to be generated, especially when there are compound faults. Height Control Sensor faults often arise without a DTC being shown.
 
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