AHC Height Sensors question

[alexchok]

Did lots of searches and found out a lot about the AHC and the height sensors, though was wondering if anyone knows the answer to the following :-

1. What happens if only 1 sensor is not working? Are there any symptoms? I tried to balance my car height (leaning on the driver side) by adjusting the sensors but it seems that no matter what I do there is always a difference in height of about 1/2 an inch. That is I've increased the height (max) on the driver's side and put it lowest on the passenger's side...no difference, just the front height increased but still leans by 1/2 an inch. Didnt touch the t-bars.

2. Took out the height sensor to check, looks pristine inside, didnt do any other tests. Just supect that one of the sensors is not working cos the front does increase/ decrease in height when adjusting the sensor, but there is still a 1/2 inch lean despite different combinations on both sides. Changes from Hi to Lo without any problems.

3. Was thinking of doing a pressure test to check the t-bars and actuators using a hydraulic brake gauge. Does doing the test on the DS means the reading is for that side or overall on both sides...err if you get what I mean.

Thanks in advance.

 

[RoderickGI]

I assume you are talking about the front sensors, right? The vehicle should balance left to right based on the sensor inputs, as you expect. It could be that something else is wrong with the front end geometry. Are you testing on a flat, level surface?

I don't know if it can be done easily, since I haven't had a close look at my front sensors but can you swap sensors left to right and see if the problem persists? If you can, and it does, then the problem isn't the sensors.

BTW, where are you located, America, Australia, England? Vehicles are set up for driving on one side of the road, taking into account camber of the roads. Maybe this has some bearing on your problem.

 

[r3run33]

what year do you have? mine is an 06 lx and has a lean from time to time; I'm frustrated and just will switch out to a regular susp. dont have the time yet to do the swap. not sure if this may help you but mine seems not to be able to balance itself out. meaning my driveway is sloped down and away so the right rear always wants to be a bit higher all the time because of the way i park. now when i strat and go it someties balances out but other times it does not. the system should have a "set" setting from the factory for a balanced position for it to go to. i think one of your pumps might be bad? keep us informed what you determine is wrong; now i feel the research and actual fix maybe do expensive and time consuming to fix. if you are doing it as in a investigating issue then i hope it works out. I love my truck and this seems to be the only defect problem with it that will break. obviously the front diff is a wheeling problem that may come out from usuage, but the ahc is killer for these vehicles.

 

[uHu]

U have to balance with the torsion bars.

When not in a curve, the fronts are "hydraulically" connected, so when checking the AHC pressure, you will get the same reading left and right. And when cranking the left bar, the right side Neutral Pressure will change as well.

Before I actually did check the Neutral Pressure and adjust the steel springs, I assumed it was like Roderick says in his first para. But, to my surprise, it wasn't.
I don't know exactly how it works with pressure difference between left and right, and how fast the fluid can move over. But there are lots of valves, and some kind of function preventing rolling and pitching. E.g sensors for "more that 30 degrees steering wheel turn", brake signal goes to the AHC ECU as well, and acceleration signal from the engine ECU. There is also some function that is controlled by the difference in input from the three height sensors.

So, lean is an easy fix. Crank the TB. Then, if you measure the Neutral Pressure like you suggest, you will optimize the system, and the comfort. When doing the back, I forecast that you will find a need to change the coil springs if the car is a few years old.
Do us a favor and put some details in you signature line.

Edit:
And yes, if only one sensor is malfunctioning, the whole system will go like bazookas, or in limp. Been there.

 

[RoderickGI]

I will soon be doing a pressure test all around on the AHC, before doing an upgrade to overpressured hydraulic accumlators (Actuator pressure globes) from B&B Suspension, so I will learn some more when I do that.

I'm just waiting for delivery of a Brake Pressure Test Kit to do the pressure testing, before ordering from B&B. I prefer to pressure test at each Actuator bleed point using pressure gauges rather than using the electrical test method, since I will be having the globes overpressured to support the extra weight of all the gear I have on the LX.

I will be adjusting the Torsion Bars to support the extra weight, so that the AHC only has to provide the minimum pressure to lift the LX to Normal and High. So I'll level it at the same time, and see if the pressures are the same on each side.

My LX does seem to sit low to the right a little sometimes, but appears to right itself once running and given a chance for the AHC to work. In my case the lean could just be because I only have one spare wheel on it at the moment, on the right.

r3run33, you can't just replace the AHC with standard suspension. The AHC is an integral part of the vehicle stability control, resisting body roll and helping to prevent rollovers. Read your manual, and then search around here and on the internet. While you will probably find people who have done it, you will find many more advising against it.

 

[r3run33]

the switch i am talking about is switch the shocks and torsions bars and by-passing the entire adaptic ahc by disconnecting it. I do understand all the things it does but at a cost of2 or 3000.00 i do not think its worth it. I have had the entire globes and pumps replaced under warranty but I am out of warranty now. I understand what I would be giving up; but at some point the cost of maintaining this system over rides the benefits

 

[r3run33]

forgot to add this please keep us updated on the tests you do roderick; also let us know about the new system you put in.

 

[r3run33]

what uhu mentioned i do know that the 06 and 07 modls made a huge jump in what the system did whith respects to the vehicle. older models this a simple hydralic lift for the entire truck when low range was engaged and did not alter the vehicle in regular modes.

 

[uHu]

r3run33, you can't just replace the AHC with standard suspension. The AHC is an integral part of the vehicle stability control, resisting body roll and helping to prevent rollovers. Read your manual, and then search around here and on the internet. While you will probably find people who have done it, you will find many more advising against it.

After removing the ahc "shocks", springs (TB & coil) and rear stabilizer bar, and fitting standard (non AHC) springs, shocks and rear stab.bar, there is no difference to a standard suspension LC. Except som dangling ahc bits not in use, and the rear "rubber springs" (those inside the coil springs).
So, if a non-ahc cruiser is ok; so is a non-ahc cruiser.


When using upgraded springs together with the AHC, remember that the AHC needs a certain part of the load to function properly as shock absorbers.

For your (cruiser's) overweight problem, this thread by dinibili is a good read, together with a few others where he has posted. https://forum.ih8mud.com/100-series...stle-overweight-lx-470s-lcs-ahc-part-1-a.html

 

[RoderickGI]

On the LX470, even my old 1998 model, the AHC is a bit more than just a hydraulic lift, in that it will compensate for body roll, try to level the vehicle, and so on. This is more important for an LX470 than a LC100 because the LX470 is more top heavy. Lexus get all nervous if you talk to them about removing the AHC, because they think the truck will fall over.

I understand that you can do it though, and probably easier on a LC100 than an LX470.

Thanks for the link to that thread uHu. I hadn't seen that one. I did investigate airbags back in 2003 when I added all the gear the vehicle currently has on it (see garage pictures), but I didn't find anyone who could provide a satisfactory solution, or was brave enough to even propose one. I had ARB install OME 862 springs which have the same free length as the original springs but a (much) higher spring rate, so don't effect the normal ride height too much, and do support additional weight quite well when the LX470 is loaded. The rear does sit a little higher than standard with no load, but it isn't an issue. If I keep the long range tank filled, the LX sits just about level at the standard heights, front and rear. The AHC will still drop down to the low position even when the LX isn't fully loaded, and will raise to the high position even when loaded.

My LX has never dropped to the low position due to overloading, and has handled off roading all around Australia. It weighs in at about 3200 Kg with a full fuel load and me in it, and 3500 Kg with a full travelling load. The AHC has handled the extra weight fine most of the time, although during heavy off roading the pump did occasionally struggle to keep the pressure up. Once or twice after a hard work out it refused to raise to the high position for a river crossing, unless I gave it a rest first. The LX has some protection built in so that the pump isn't run constantly, and serious off roading can overwork the pump.

That is why I want to install overpressured Actuator Pressure Globes, to give the pump a rest from topping up the pressure constantly, and provide a full range of travel even with the extra weight. The system will run at a higher maximum pressure, which he pump will have to provide, but once the pressure is in the Accumulator and Actuator Globes, they can support the vehicle. The pressure when running at normal height should actually be lower than standard, once I adjust the TBs to support more of the weight. The higher pressure in the Actuator globes is needed to ensure there is still some travel available to allow the shocker absorber to function, even when the vehicle is fully loaded and raised to the high position. That is when the AHC will be doing most work, and the oil pressure will be highest, because the springs will be doing the least work when they are fully extended. I just need to make sure that the pressure is high enough to allow the AHC to act as shock absorbers, as you say, and also high enough so that there is still some pressure in the system when the AHC is put in the low position, when the springs will be supporting most weight.

I need to replace the globes anyway because the OEM ones have lost their gas charge, and it didn't seem to make sense to install OEM ones again, when I can get overpressure ones. Not to mention that Lexus globes cost a fortune.

I'll probably start a thread of my own once I have the Brake and ABS Pressure Test Kit I need to test the hydraulic pressures. It is on the way from the USA now.

 

[alexchok]

U have to balance with the torsion bars.

When not in a curve, the fronts are "hydraulically" connected, so when checking the AHC pressure, you will get the same reading left and right. And when cranking the left bar, the right side Neutral Pressure will change as well.

Before I actually did check the Neutral Pressure and adjust the steel springs, I assumed it was like Roderick says in his first para. But, to my surprise, it wasn't.
I don't know exactly how it works with pressure difference between left and right, and how fast the fluid can move over. But there are lots of valves, and some kind of function preventing rolling and pitching. E.g sensors for "more that 30 degrees steering wheel turn", brake signal goes to the AHC ECU as well, and acceleration signal from the engine ECU. There is also some function that is controlled by the difference in input from the three height sensors.

So, lean is an easy fix. Crank the TB. Then, if you measure the Neutral Pressure like you suggest, you will optimize the system, and the comfort. When doing the back, I forecast that you will find a need to change the coil springs if the car is a few years old.

Thanks uHu, but I did read some of your posts from when I was searching and you mentioned that if we cranked the TB, then the pressure would be off, and that the car would stabilize itself based on the height sensors (with the same lean) when started up again. I saw a lot of posts specifically warning against cranking the TBs for an AHC suspension. Pls help shed some light here.

Anyway, I get what you mean, we crank up the T-Bars so that both sides are even, then adjust the height sensors to get optimal pressure.

Problem is :- I dont have a pressure gauge yet , and secondly, so what does the difference in the height sensors between Front Left and FR mean??

Do us a favor and put some details in you signature line.

Edit:
And yes, if only one sensor is malfunctioning, the whole system will go like bazookas, or in limp. Been there.

I have a stock LX470, I do have it in my sig, but I'll go have a look at it again. Thanks man.

 

[alexchok]

I assume you are talking about the front sensors, right? The vehicle should balance left to right based on the sensor inputs, as you expect. It could be that something else is wrong with the front end geometry. Are you testing on a flat, level surface?

I don't know if it can be done easily, since I haven't had a close look at my front sensors but can you swap sensors left to right and see if the problem persists? If you can, and it does, then the problem isn't the sensors.

BTW, where are you located, America, Australia, England? Vehicles are set up for driving on one side of the road, taking into account camber of the roads. Maybe this has some bearing on your problem.

I'm located in Malaysia, RHD, the car was imported from Australia by the previous owner, and yeah I'm testing it on a flat surface.. still curious what the height sensors really do. I can't swap them because they install differently but I dont think they are malfunctioning since they dont exhibit any of the symptoms like what uHu says... phew...

 

[1loudLX]

Lexus get all nervous if you talk to them about removing the AHC, because they think the truck will fall over.

Lexus gets nervous if you talk about putting a bike rack on a LS430(been there). How is the LX470 more top heavy then a LC100? The two or three extra ECUs, better carpet and leather? Or is it the wood trim that makes it more top heavy? I'm being serious here. I doubt the plastic cladding on the outside and addition of a few extra chrome strips adds up to be that much more top heavy.

 

[uHu]

For adjusting the Neutral Pressure, the Factory Service Manual says to connect the pressure gauge to EITHER left or right front actuator bleeder, then to let the ahc lift the truck from Lo to Hi, stop the engine and then adjust any difference in height between left and right by turning the torsion bar adjusters. When the sideways height difference is less than 10 mm, let the ahc lower to Lo, lift to Hi, and then read the pressure. Should be 5.7 +- 0.3 MPa (825 +- 43 psi).

I tried to adjust and measure separately left and right, but the reading was always the same on both sides, and the turning of one TB affected the other side as well. So I trusted the book.

Remember to take the load off the front wheels completely before cranking the T-bars.

There is no problem adjusting the TBs to level the truck without using a pressure gauge. If you want to be certain not to change the pressure, just adjust the two TBs opposite way by the same amount until the truck is level. From experience (my limited) I would expect a requirement for tightening the TBs a turn or two after sitting on them for a few years. Best thing is to check the pressure. Easy job. Just get a LSPV gauge kit. Fits the purpose.

 

[cmfhsu]

Lexus gets nervous if you talk about putting a bike rack on a LS430(been there). How is the LX470 more top heavy then a LC100? The two or three extra ECUs, better carpet and leather? Or is it the wood trim that makes it more top heavy? I'm being serious here. I doubt the plastic cladding on the outside and addition of a few extra chrome strips adds up to be that much more top heavy.

The lx470 does have thicker glass, though that isn't really THAT big of an issue. Mostly what it is is lexus assumes the worst and thinks you're the 80 year old granddad who is gonna try to haul his harley around on the roof. Thus the hesitancy and everything.

 

[RoderickGI]

How is the LX470 more top heavy then a LC100? The two or three extra ECUs, better carpet and leather?

All the things you mention, but mostly soundproofing, including thicker glass, which is both high and heavy.

I don't have the reference right at hand, but I read it recently, and it made sense to me. The Sahara LC may come close, but you know Lexus like to provide a nice, quite ride.

A comparison of Tare and Gross weights might show up how different they are. I'll let you do it, if you wish.

 

[hoser]

For the record, the 2000 LX weighs in at 5401 lbs versus 5115 lbs for the same year LC. So less than 300 lb difference. For 2007, the difference is 165 lbs.

 

[alexchok]

There is no problem adjusting the TBs to level the truck without using a pressure gauge. If you want to be certain not to change the pressure, just adjust the two TBs opposite way by the same amount until the truck is level. From experience (my limited) I would expect a requirement for tightening the TBs a turn or two after sitting on them for a few years. Best thing is to check the pressure. Easy job. Just get a LSPV gauge kit. Fits the purpose.

Thanks! Now I feel better about adjusting the TBs. Before, I was just fiddling with the Height Sensors but it didn't work, the overall front height would increase or decrease when I adjusted the height sensors, but the sideways difference would always remain no matter what combinations I did with the front L and front R sensors.

I still can't figure out what effects different settings on the front L and front R height sensors do...

 

[r3run33]

this is why i love the site you get so much info here! hey roderick what globes are you going to get?? what company? let us know how it works out. uhu my switch is a last resort to go to the regular set up not there yet. also for loud my old lx did not do the movements that my 06 does. i had a 99 before and i used the ahc only when off roading. now i'm not a hardcore off roader, just some times and in the 90,000 miles i put on her i never experienced any of these problems that i've had with the 06. i'm at 50,000 now

 

[r3run33]

i dont want to start an argument but i really dont think the ahc systems between 06 07 models and earlier years are the same. Any guru's available to help out with this?? this is not an arguement over which is better.