Quick question about AHC ride with extra weight (1 Viewer)

Joined
Sep 24, 2020
Messages
5
Location
NE. OHIO
Hey guys, I have a 2006 land cruiser and I like the ride on it for the most part but I feel I may be missing out on something due to having AHC problems. Everyone says the land cruisers ride like clouds, but its not all THAT smooth to me. It rides pretty good, but only slightly better than my 2003 stock 4runner that I traded for this 100 series.
My 100 won't drop to low or lift up to high. This isn't a huge issue to me if its not causing any deficit in the ride. But, I had never ridden in a land cruiser prior to buying this one and I have never ridden in any other land cruiser so I don't have anything to compare it to.

After starting my car and driving for a few seconds, the AHC OFF light flashes constantly. I had this checked by a Toyota dealership and they said it was all of the height sensors. Does this sound right? That ALL of the sensors are bad? Or is it a fluke?

I'd love to get this thing working 100%, but I can deal with non-working AHC for now.

My main question is about riding with passengers in the 2nd row seats. When I have passengers in the second row, the ride gets very bad and I feel bad for the people in the back. It feels like the suspension is bottoming out with no more than 500 lbs in the back seat. This can't be right as I know the towing capacity is way more than that and I know that this thing is rated for more than just a measly 500lbs of human flesh bags in the back. Its actually more like 400lbs. Could this rough ride be due to a failing AHC system? It doesn't ride bad with myself and another in the front seats.

Also, does the ride stiffness control knob (next to the AHC position button) work if the AHC height sensors are bad?

I'd like to mention also that my AHC height control has never worked since I bought this about 7 months ago.
 
Joined
Jan 19, 2006
Messages
232
Location
Santa Cruz, CA
Yeah, it shouldn't be ridding rough. Your passengers should be lulled to sleep by how smooth an quiet your Cruiser is.

The OFF light will flash if just one sensor is messed up. It doesn't mean they all are. Techstream should help you figure that out. The stiffness control won't work if the system has shut itself off, as far as I know.

Tons of info here in the forum. Access to techstream is key like @ramangain said.

Probably start with this:


And this:

 
Joined
Sep 15, 2016
Messages
763
Location
Durham, NC
I would definitely change the fluid as step 1 then maybe just baseline the sensors with new ones. They’re relatively cheap.

if you have a LC shop nearby they may be able to help or post in the Ohio clubhouse to ask if someone local can lend a hand.

I would also search techstream on this forum and get that setup so you can see what the pressures are. That will give you some insight into the condition of the sensors.
 
Joined
Sep 24, 2020
Messages
5
Location
NE. OHIO
Wow, thanks for the quick replies everyone. I did see one member posted a very long video about techstream and adjusting things on the land cruiser some time ago. I figured mine wouldn't register the pressures because I can't switch out of the neutral position on the AHC height. I've also seen videos where certain versions of techstream won't work with certain years of land cruisers. I have a 12 hour drive coming up later this year and I'll be taking 3 others with me so I'm hoping to have it riding like a cloud by then.

@ramangain, I could make the trek. I don't mind driving and I work a 24/48 schedule so I have plenty of time between work days. Send me a message and we can figure out a day!
 

LndXrsr

AHC Aficionado
SILVER Star
Joined
May 3, 2020
Messages
347
Location
Cincinnati
If you’re ever down in Cincinnati, I’d be happy to help look at it with you.

First steps are flush the fluid and get access to Techstream readings in some way. You won’t be able to check pressures if you can’t move L to N, but you can get love sensor readings which could point you to which sensor(s) is/are problematic. Read my ABCs of AHC for more options besides Techstream that you can use to get readings.

Tightening your front torsion bars a few turns equally on both sides might also relive enough AHC pressure to at least allow you to move up and down if an overloaded system is the issue. This is less likely since you can’t move down to L however.
 
Joined
Dec 6, 2016
Messages
316
Location
Brisbane, Australia
Hey guys, I have a 2006 land cruiser and I like the ride on it for the most part but I feel I may be missing out on something due to having AHC problems. Everyone says the land cruisers ride like clouds, but its not all THAT smooth to me. It rides pretty good, but only slightly better than my 2003 stock 4runner that I traded for this 100 series.
My 100 won't drop to low or lift up to high. This isn't a huge issue to me if its not causing any deficit in the ride. But, I had never ridden in a land cruiser prior to buying this one and I have never ridden in any other land cruiser so I don't have anything to compare it to.

After starting my car and driving for a few seconds, the AHC OFF light flashes constantly. I had this checked by a Toyota dealership and they said it was all of the height sensors. Does this sound right? That ALL of the sensors are bad? Or is it a fluke?

I'd love to get this thing working 100%, but I can deal with non-working AHC for now.

My main question is about riding with passengers in the 2nd row seats. When I have passengers in the second row, the ride gets very bad and I feel bad for the people in the back. It feels like the suspension is bottoming out with no more than 500 lbs in the back seat. This can't be right as I know the towing capacity is way more than that and I know that this thing is rated for more than just a measly 500lbs of human flesh bags in the back. Its actually more like 400lbs. Could this rough ride be due to a failing AHC system? It doesn't ride bad with myself and another in the front seats.

Also, does the ride stiffness control knob (next to the AHC position button) work if the AHC height sensors are bad?

I'd like to mention also that my AHC height control has never worked since I bought this about 7 months ago.

To add to the replies already received -- with late edit, additional paragraphs added ….

If the AHC light is flashing, then the Active Height Control (AHC) part of the system is not working, which is why there is no response to LO and HI height selections. There also will be no response to the four-position “Comfort . . Sport” switch. It also means that the “Toyota Electronic Modulated Suspension” (TEMS) part of the system is not working and that the system is likely to be in one of several ‘fail safe modes’ where ‘fail safe’ means preventing system damage and preventing the vehicle becoming unsafe in some way.

TEMS provides adaptive variable suspension by varying the damping characteristics through 16 steps in real time while the vehicle is being driven – if the system is working correctly. In the most common ‘fail safe mode’, the TEMS system will adopt and remain in step 8 of the 16 damping steps and the AHC system will not operate but will remain in standard “N” height. In this condition, the ride usually will feel more harsh than expected at town speeds (because the damping is too hard when fixed at Step 8) and may wallow at highway speeds (because the damping is too soft when fixed at Step 8).

One easy indication of such a non-operating condition is whether the vehicle settles lower when loaded and does not self-adjust to “N” height as it should – such as when passengers are on board in the rear seats. The vehicle is meant self-adjust regardless of load but within these load limits:

AHC Limits.jpg


Note: The loads include everything in or on the vehicle – driver, passengers, luggage, fuel, modifications, accessories and fittings – everything.

To better understand the system, it is helpful to print and read the General Description of the operation of the AHC/TEMS system – this can be found at the following link. (This might seem to be an old link but there have been no significant changes in the way the AHC/TEMS system works on LC100/LX470 vehicles since these systems were first introduced). The link is to the genuine multi-year Toyota LC100 Factory Service Manual (FSM). The extract above comes from this link.

https://lc100e.github.io/manual/
Go to tabs at Index Panel, top left of opening page -- New Car Features (first item in the list) > CHASSIS > Suspension > Active Height Control Suspension & Skyhook TEMS.

So what causes a ‘fail safe condition’ with symptoms like those described?


The most common causes are:

Overload leading to excessive AHC pressures beyond the specification range – this may be due to simple overloading beyond the limits of the system. Or it will happen anyway, even with 'normal' loads, as the vehicle ages and the ‘spring rates’ of the front torsion bars and rear coil springs progressively soften and carry less load, meaning that the AHC system inevitably carries more load. So the AHC pressures rise naturally over the years with the aging of the vehicle and its mechanical torsion bars and springs. Eventually, the AHC pressures will be found to be beyond the FSM-specified range. The front AHC pressures can be reduced easily by using the torsion bar adjusters to increase load carried by the torsion bars and reduce load carried by the front AHC system and thereby reduce front AHC pressure. The rear is not so easily adjustable and may require ‘spacers’ to pre-load the rear coil springs to increase the load they carry and reduce the rear AHC pressure, or, replacement rear coil springs, possibly upgraded, may be the answer.

One or more problematic Height Control Sensors – the AHC Electronic Control Unit (ECU) relies, among other things, on correct signals from the three Height Control Sensors – Front Right, Front Left and Rear (one only). It only takes one faulty Height Control Sensor, or large differences between wrongly adjusted Sensors, to cause conflicting inputs to the ECU and for the ECU to put the system into ‘fail safe mode’ (as described above) until the fault is corrected.

There are the most common causes and need to be resolved first before looking for other more complex causes. Other causes can be studied in the FSM – see reference list below.

It is also worthwhile to check whether the vehicle has been cross-levelled correctly – meaning static front hub-to-fender heights are equal within 10 millimetres (0.39 inches), less is better, with engine “OFF” – and also worthwhile to check that front and rear ‘operating heights’ are correct with engine "ON" and suspension settled – for a stock vehicle: front 19.75 inches, rear 20.5 inches, hub-to-fender, with the vehicle empty (or with usual ‘fixed’ loads such as armour etc already compensated by correct springs, torsion bar adjustment) but no added variable load, no pax, fuel full, on level ground, previously cross-levelled correctly.

The point here is that ‘height’ and ‘AHC pressure’ are interdependent – unless changes are made to compensate, more height means more AHC pressure, less height means less AHC pressure. AHC pressures which are too low or too high will result in poor damping performance – AHC pressures must be kept within the FSM-specified ranges, preferably towards the low end, for best damping and best ride comfort.

Unless the maintenance record shows that ‘globes’ have been replaced recently, they may be past their best and replacement may be necessary at some time. The test of overall condition of ‘globes’ is observation of AHC Tank levels at “HI” and “LO” heights. Backlight the tank with a torch from behind or through the cap if the fluid is old and dark. (New fluid is a light pink). Difference of 14 graduations means ‘globes’ are as new, 7 graduations means time to replace ‘globes’ because too much nitrogen has been lost from behind the membranes. ‘Globes’ are ‘wear items’, so this happens eventually. This test cannot be made until AHC will raise and lower and so this must wait until other problems are resolved and corrected.

Note that poor condition of ‘globes’ does not prevent AHC raise-lower operation.

However, poor ‘globe’ condition certainly will adversely affect damping performance and cause a rough, ‘springy’ ride.

Some further references:

Owner’s Manual:


If not at hand, this link to the Owner’s Manual and Maintenance Schedule for your vehicle may be useful.
Toyota Warranty & Toyota Manuals | Toyota Owners - https://www.toyota.com/owners/resources/warranty-owners-manuals

AHC Diagnostics:

https://lc100e.github.io/manual/
At this link, use the Index on the left hand side of the opening page and follow these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS

AHC On-Vehicle Inspection including correct AHC pressure ranges:


https://lc100e.github.io/manual/
At this link, use the Index on the left hand side of the opening page and follow these tabs:
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM (Independent Front Suspension) > ON-VEHICLE INSPECTION


BROADCASTING AGAIN THE GOLDEN RULE: ALWAYS HAVE JACKSTANDS UNDER THE CHASSIS RAILS WHEN WORKING UNDER THE CAR ON THE AHC SYSTEM
– and yes, this is shouted in bold capitals not to be offensive but for good reasons, cannot be repeated often enough. Accidents do happen. A hard barrier -- such as fixed, lockable stands secure at the chassis rails, certainly not jacks -- is a ‘must have’ to ensure that an unexpected to descent of the car body onto a human body is impossible.
 
Last edited:

suprarx7nut

The YotaMD Guy
Supporting Vendor
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Messages
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Colorado
Lots of help so far. Awesome crowd here to support you. Sounds like a little amount of careful diagnostics and some routine baselining might be all you need. If the globes are of unknown age, that's a likely replacement need now or in near future. ~$750 shipped for a full set on those.

Let us know how it goes!
 
Joined
Dec 6, 2016
Messages
316
Location
Brisbane, Australia
Lots of help so far. Awesome crowd here to support you. Sounds like a little amount of careful diagnostics and some routine baselining might be all you need. If the globes are of unknown age, that's a likely replacement need now or in near future. ~$750 shipped for a full set on those.

Let us know how it goes!
To @ParaJake :

@suprarx7nut has not mentioned it so I will -- if not already seen, his excellent video and "Cheat Sheet" is recommended as part of your AHC/TEMS 'general education' and on the specifics of adjusting the system -- see
Builds - The YotaMD Build - Cypress - https://forum.ih8mud.com/threads/the-yotamd-build-cypress.1184210/page-9#post-13383404

The two links mentioned by @JJ_SC at Post#3 above also are important. The "ABCs of AHC" thread initiated by @LndXrsr is succinct and most worthwhile. The "Definitive List of Maintenance Issues" is now a long and unwieldy thread -- but it is part of a long-term permanent IH8MUD record on AHC/TEMS matters and there is a lot of good information in there. There are many other helpful threads -- but maybe that is enough 'information overload' for a start!!
 

ramangain

Clarksonian disciple
SILVER Star
Joined
Feb 6, 2020
Messages
2,542
Location
Atlantis
I was messaging with the OP offline and pointed to him an appropriate TS + cable combo. I think he's got loads of info to go in the right direction, including offers of video conference support if things get dicey.

Great AHC support in this forum from the comfort of your own garage/driveway
 

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