Intro and yet another AHC thread…

Joined
Apr 6, 2022
Messages
8
Location
Maine
Hello All,

New member here, but I’ve been lurking for over a year, and have learned more about this truck here than anywhere else. This place is great! My truck is a 2006 Land Cruiser - 216000 miles (on the dot when I just went to check!) and I’ve owned it for about a year and a half. I’ve put about 17,000 miles on it in that time. The truck grew up in Connecticut until moving to Maine a couple of years ago. I don’t know a lot about the history of the truck, but I do know the former owner, so I can probably find things out if needed. When it moved to Maine it was garage kept and hardly used, but the garage was next to a salt pond. Once I took ownership I had to park it outdoors next to the ocean for 5 months a year for my job. I’m sure that salt air is gonna haunt me throughout the rest of this trucks life. During the off season it mostly lives in my garage, with the occasional road trip to Boston or Philadelphia. I avoid driving in the snow as much as possible, but salty roads are hard to avoid. Yay salt. But enough about me, and on to my troubles…
I’m sorry to start yet another AHC thread, but I’ve dug through a bunch of threads, and frankly, it’s pretty overwhelming trying to sort through everything, and I’m at my wits end.
Here’s what’s going on: a couple of weeks ago I was driving and all of a sudden, things didn’t feel quite right with the suspension. Very bouncy in the rear. When I got home I took one look at the outside of the truck and the rear was noticeably lower than the front. First thing I did was browse these forums, and armed with a small amount of knowledge (due to quick browsing, not for lack of a wealth of knowledge contained within!), went out and cycled the AHC through Neutral, Low, and High. ‘Low’ was adequately low in the front and the rear, ‘High’ was adequately high in the front and the rear, ‘Neutral’ looked okay in the front, but the rear was as low as it was in ‘Low’.

Back to the forums!

Read a bunch, ordered a Mini-Vci cable, dowloaded Techstream from the link found in this forum, and went to work trying to figure things out. I have not yet tried everything, but my guess from what I’ve read is that the rear sensor is the culprit, but I want to get some opinions here before ordering a new one.

Fluid levels:

In ‘Low’ the fluid looks to be right at the seam of the reservoir, so above any graduation marks.

In ‘Neutral’ the fluid is just about at the highest graduation mark.

In ‘High’ the fluid level is at about the 4th or 5th graduation mark (this seems to vary slightly during different tests).

Techstream data:

‘Neutral’ - Initial reading, normal load, no one in the car

-FR Height Control Sensor: 0.2

-FL Height Control Sensor: 0.1

-RR Height Control Sensor: -0.4

-Front Pressure Sensor: 0.0

-Rear Pressure Sensor: 0.0

-Accumulator Press Sensor: 0.0


‘Low’

-FR Height Control Sensor: -2.0

-FL Height Control Sensor: -2.0

-RR Height Control Sensor: -0.4

-Front Pressure Sensor: 0.0

-Rear Pressure Sensor: 0.0

-Accumulator Press Sensor: 0.0


‘High’

-FR Height Control Sensor: 1.5

-FL Height Control Sensor: 1.3

-RR Height Control Sensor: 1.7

-Front Pressure Sensor: 9.8

-Rear Pressure Sensor: 8.1

-Accumulator Press Sensor: 10.5


‘Neutral’ again

-FR Height Control Sensor: -0.0

-FL Height Control Sensor: -0.1

-RR Height Control Sensor: 0.2

-Front Pressure Sensor: 9.8

-Rear Pressure Sensor: 8.1

-Accumulator Press Sensor: 10.5


Seemed odd to me that the last three data points didn’t change, so I turned the car off and back on and rescanned.

‘Neutral’ after turning car off and back on

-FR Height Control Sensor: -0.1

-FL Height Control Sensor: -0.2

-RR Height Control Sensor: -0.4

-Front Pressure Sensor: 0.0

-Rear Pressure Sensor: 0.0

-Accumulator Press Sensor: 0.0


I have not removed the rear sensor yet. Things are pretty rusty under there and I haven’t had the courage to wrench on those bolts yet. I did take the cover off and the springs are bright and shiny. I sprayed some contact cleaner in there and used a pencil eraser on the traces on the cover, but nothing changed. Haven’t tried an ohm meter yet.

So my question is, could this be anything other than the rear sensor? I’m assuming that since the fluid level seems ok (if not a bit high) and I can raise the truck all the way up that the globes and accumulators are fine, but I don’t really know much about how the system works in that regard.

Thanks for any help. Sorry again for another AHC thread. Maybe I need to learn how to search better.

-Mike
 

Red Beard

Cruisin'
Joined
Aug 23, 2007
Messages
964
Location
Kennett Square, PA
Welcome! Let's see that thing!

Lots of AHC info around here. I think we can probably do new members some favors by updating the FAQs to the latest info.

The pressures readings you want to pay attention to is when you cycle from Low to Neutral.

This cheat sheet is a helpful step by step for the graduation test and the pressure tests:

Bouncy rear normally points to bad globes. You can get all 4 of them for ~$600 from Impex Japan. Search for the thread on that.

I have an 2006 at 210k. I just did fluid, globes, rear springs, and added 30mm spacers. I'm now in spec with some rake, drives great. Still a little harsh in some conditions but I'm pretty sure thats my aging shocks (and their aging bushings) which I haven't gotten the courage to replace yet. :eek:
 
Joined
Apr 6, 2022
Messages
8
Location
Maine
Thanks Red Beard. Here she is:
70CFDF0E-C884-472A-B5E4-7C8ED9CF2E0B.jpeg


I have seen both of those links you posted, but part of my problem is that I can’t remember where I saw information that I read, and some of these threads are 1000 replies deep. I realize adding another thread probably doesn’t help the matter.

Also, I’m pretty sure I read somewhere here that a bouncy rear means a bad sensor, but of course I can’t find that again 🤷🏻‍♂️

I am also reading a lot of people indicating that fluid levels like mine indicate the globes are ok.

I’m just trying avoid throwing a ton of money at this, chasing an elusive problem.

I think my best next move would be to break out an ohm meter and test the sensor.

I’ll also go back through the links you posted and see if I can gain any more insight.

Thanks again for your input!
 
Joined
Oct 8, 2018
Messages
240
Location
N. Texas
Do the pressure check going from low to neutral. That will give you the proper results to compare.

Second it sounds like you have too much fluid in the reservoir. Low should show near the top graduation, not above.

Once you have the fluid level right, you'll be able to count the graduations between low-high.

That said, I had similar symptoms with the rear suddenly being low. I knew I only had 6-7 graduations of fluid, so I replaced the globes and all is now well. Ofcourse, I made sure the pressures were correct first.
 
Joined
Oct 21, 2020
Messages
236
Location
MS
Check for fluid leaks, rusted lines, leaking shocks, etc... If all of that is good and assuming your pressure numbers are correct then I would go with new globes and rear springs to get the rear in spec, then crank the torsion bars on the front to get the front in spec. Also do a complete fluid flush, If there's as much rust under there as you say there is though then it might be better to just swap over to a conventional setup.
 

Red Beard

Cruisin'
Joined
Aug 23, 2007
Messages
964
Location
Kennett Square, PA
Thanks Red Beard. Here she is:
View attachment 2973773

I have seen both of those links you posted, but part of my problem is that I can’t remember where I saw information that I read, and some of these threads are 1000 replies deep. I realize adding another thread probably doesn’t help the matter.

Also, I’m pretty sure I read somewhere here that a bouncy rear means a bad sensor, but of course I can’t find that again 🤷🏻‍♂️

I am also reading a lot of people indicating that fluid levels like mine indicate the globes are ok.

I’m just trying avoid throwing a ton of money at this, chasing an elusive problem.

I think my best next move would be to break out an ohm meter and test the sensor.

I’ll also go back through the links you posted and see if I can gain any more insight.

Thanks again for your input!
Love the color. One of my faves.

Seeing that photo you can already tell it's sitting too low in the back. Could be a myriad of things. Follow the steps others have given above to get proper readings and go from there.

I think bad sensors will throw crazy numbers resulting in the AHC giving up. Judging by the info you gave the sensor readings are normal.

New springs, at least, are probably in your future. 30mm spacers help too (I did ironman). Globes will really do the trick. Get ready to crank some torsion bars too! ;)
 
Joined
Apr 6, 2022
Messages
8
Location
Maine
I hooked up Techstream again, put the AHC in Low and these are the readings:

FR Height Control Sensor: -1.9
FL Height Control Sensor: -2.0
RR Height Control Sensor: -0.4
Front Pressure Sensor: 0.0
Rear Pressure Sensor: 0.0
Accumulator Press Sensor: 0.0

Then I moved to Neutral and this is what I got:

FR Height Control Sensor: -0.0
FL Height Control Sensor: -0.2
RR Height Control Sensor: -0.4
Front Pressure Sensor: 7.4
Rear Pressure Sensor: 0.0
Accumulator Press Sensor: 0.0

So no change in the Rear Pressure Sensor. Is that still indicative of a globe issue, or should I focus on the sensor?

I was concerned that there was too much fluid, but in the video that goes along with AHC Info Cheat Sheet (YotaMD) link above, his fluid is even higher than mine.

I have seen no evidence of any fluid leaking onto the garage floor, but I will do a more thorough inspection of the lines later today or tomorrow. I had a brake line rust through last year, so I wouldn’t be surprised if something similar happens to the AHC.
 
Joined
Dec 6, 2016
Messages
705
Location
Brisbane, Australia
Hello All,

New member here, but I’ve been lurking for over a year, and have learned more about this truck here than anywhere else. This place is great! My truck is a 2006 Land Cruiser - 216000 miles (on the dot when I just went to check!) and I’ve owned it for about a year and a half. I’ve put about 17,000 miles on it in that time. The truck grew up in Connecticut until moving to Maine a couple of years ago. I don’t know a lot about the history of the truck, but I do know the former owner, so I can probably find things out if needed. When it moved to Maine it was garage kept and hardly used, but the garage was next to a salt pond. Once I took ownership I had to park it outdoors next to the ocean for 5 months a year for my job. I’m sure that salt air is gonna haunt me throughout the rest of this trucks life. During the off season it mostly lives in my garage, with the occasional road trip to Boston or Philadelphia. I avoid driving in the snow as much as possible, but salty roads are hard to avoid. Yay salt. But enough about me, and on to my troubles…
I’m sorry to start yet another AHC thread, but I’ve dug through a bunch of threads, and frankly, it’s pretty overwhelming trying to sort through everything, and I’m at my wits end.
Here’s what’s going on: a couple of weeks ago I was driving and all of a sudden, things didn’t feel quite right with the suspension. Very bouncy in the rear. When I got home I took one look at the outside of the truck and the rear was noticeably lower than the front. First thing I did was browse these forums, and armed with a small amount of knowledge (due to quick browsing, not for lack of a wealth of knowledge contained within!), went out and cycled the AHC through Neutral, Low, and High. ‘Low’ was adequately low in the front and the rear, ‘High’ was adequately high in the front and the rear, ‘Neutral’ looked okay in the front, but the rear was as low as it was in ‘Low’.

Back to the forums!

Read a bunch, ordered a Mini-Vci cable, dowloaded Techstream from the link found in this forum, and went to work trying to figure things out. I have not yet tried everything, but my guess from what I’ve read is that the rear sensor is the culprit, but I want to get some opinions here before ordering a new one.

Fluid levels:

In ‘Low’ the fluid looks to be right at the seam of the reservoir, so above any graduation marks.

In ‘Neutral’ the fluid is just about at the highest graduation mark.

In ‘High’ the fluid level is at about the 4th or 5th graduation mark (this seems to vary slightly during different tests).

Techstream data:

‘Neutral’ - Initial reading, normal load, no one in the car

-FR Height Control Sensor: 0.2

-FL Height Control Sensor: 0.1

-RR Height Control Sensor: -0.4

-Front Pressure Sensor: 0.0

-Rear Pressure Sensor: 0.0

-Accumulator Press Sensor: 0.0


‘Low’

-FR Height Control Sensor: -2.0

-FL Height Control Sensor: -2.0

-RR Height Control Sensor: -0.4

-Front Pressure Sensor: 0.0

-Rear Pressure Sensor: 0.0

-Accumulator Press Sensor: 0.0


‘High’

-FR Height Control Sensor: 1.5

-FL Height Control Sensor: 1.3

-RR Height Control Sensor: 1.7

-Front Pressure Sensor: 9.8

-Rear Pressure Sensor: 8.1

-Accumulator Press Sensor: 10.5


‘Neutral’ again

-FR Height Control Sensor: -0.0

-FL Height Control Sensor: -0.1

-RR Height Control Sensor: 0.2

-Front Pressure Sensor: 9.8

-Rear Pressure Sensor: 8.1

-Accumulator Press Sensor: 10.5


Seemed odd to me that the last three data points didn’t change, so I turned the car off and back on and rescanned.

‘Neutral’ after turning car off and back on

-FR Height Control Sensor: -0.1

-FL Height Control Sensor: -0.2

-RR Height Control Sensor: -0.4

-Front Pressure Sensor: 0.0

-Rear Pressure Sensor: 0.0

-Accumulator Press Sensor: 0.0


I have not removed the rear sensor yet. Things are pretty rusty under there and I haven’t had the courage to wrench on those bolts yet. I did take the cover off and the springs are bright and shiny. I sprayed some contact cleaner in there and used a pencil eraser on the traces on the cover, but nothing changed. Haven’t tried an ohm meter yet.

So my question is, could this be anything other than the rear sensor? I’m assuming that since the fluid level seems ok (if not a bit high) and I can raise the truck all the way up that the globes and accumulators are fine, but I don’t really know much about how the system works in that regard.

Thanks for any help. Sorry again for another AHC thread. Maybe I need to learn how to search better.

-Mike
Welcome!! With Techstream working, you are making a great start on AHC matters already!

@Red Beard and @Coin and @jsloden have given you excellent leads, so no need to drown you in more information at this stage.

The links provided by @Red Beard are two of the vital links if you want to come up to speed quickly on AHC.

"ABC of AHC" is the "go to" thread where you will find most things in the first few pages. Start at the beginning, you won't need to read hundreds of posts -- it will become obvious when the same issues and questions start to reappear.

The video at the second link is the "go to" video on AHC adjustments. At the moment, your Front and Rear AHC pressures are way too high -- this will give you far worse damping and ride quality than the vehicle is capable of providing, and the AHC system will easily slip into overload without much more weight being added (and then it will refuse to rise or it may drop to "LO"). Ultimately, over-pressures will lead to problems such as leaky shock absorber seals and other steadily worsening problems -- so suggest this is best addressed soon.

The Rear Height Control Sensor is a common source of grief especially in wet and salty conditions and MIGHT be your current problem. The Sensor readings on Techstream look reasonable but that does not give much assurance, nor does visual inspection -- testing is necessary.

When doing Pressure readings, start the vehicle at "N" height, then drop to "LO", then raise to "N". Then leave the engine running for say 30 seconds (or longer), to be sure that the AHC Pump has finished raising the vehicle and also finished filling the Height Control Accumulator (the long cylindrical thing midway along the LHS chassis rail. Otherwise you will get spurious pressure readings. It always is a good idea to take 3 sets of pressure readings in any test for this reason.

Look for Diagnostic Trouble Codes (DTC's) on Techstream. These provide good hints about fault conditions but access to a Factory Service Manual (FSM) will be necessary to interpret them.

Meanwhile, enjoy the truck!!
 
Last edited:
Joined
Apr 6, 2022
Messages
8
Location
Maine
I have some ohm readings, but I think I want to get my hands on another ohm meter and try again. Here’s what I came up with though:

Truck in ‘High’

With the rear sensor still installed, cover off, springs removed
- pin 1 (top) and pin 2 (middle) 79.65k
- pin 1 and 3: .58k
- pin 2 and 3: 77.82k

This would be a lot easier with the sensor removed, but I’m afraid things will crumble if I breathe on it wrong. Best pic I could get of the bolts:

20FD4D95-ADEC-421F-A0B3-61D4139245AD.jpeg
 
Joined
Dec 6, 2016
Messages
705
Location
Brisbane, Australia
I have some ohm readings, but I think I want to get my hands on another ohm meter and try again. Here’s what I came up with though:

Truck in ‘High’

With the rear sensor still installed, cover off, springs removed
- pin 1 (top) and pin 2 (middle) 79.65k
- pin 1 and 3: .58k
- pin 2 and 3: 77.82k

This would be a lot easier with the sensor removed, but I’m afraid things will crumble if I breathe on it wrong. Best pic I could get of the bolts:

View attachment 2974477

It is unclear exactly what is being measured with the Sensor cover removed.

Here is a post from long ago by @PADDO which indicates what resistances should be found with the Sensor intact, meaning with the cover in place:

AHC - Sudden Loss of Functionality - HELP - https://forum.ih8mud.com/threads/ahc-sudden-loss-of-functionality-help.986894/page-2#post-10993896

“…. about 3900 ohms iirc between pins 1-3, place the wiper at mid displacement and you should read about 1950 ohms 1-2 and 2-3; gently rotate the wiper shaft and observe the resistance changes from min to ~ 3900 ohms between 2-1 and 2-3 depending on which way you rotate the wiper shaft”.

This could be done in situ by detaching the electrical connector to give access to the Sensor electrical pins to then allow attachment of the ohmmeter, and, detaching the linkage arm from the suspension Rear Upper Control Arm. Then the Sensor linkage arm can be rotated through its range while looking at the resistance, and in particular, looking to see that the resistance changes smoothly, not erratically, through its movement range. This is not the Factory Service Manual (FSM) method but it should work. The FSM method is described further below.

Another more indirect method of getting an idea of Sensor condition and performance is to perform the “Active Test” manually (not with Techstream utilities) but with Techstream also connected so that the smoothness or otherwise of the Sensor readings can be observed on the Techstream screen and also whether the Sensor readings make sense given the height of the vehicle. The manual “Active Test” method is described at section 5 – Height Control Operation (Active Test) at Page 6 of the first attachment. The Special Service Tool (SST) mentioned is simply a bridging wire – an unbent paperclip is just as good. "DLC1" is the socket with a lid marked "DIAGNOSTIC" in the engine bay above the RHS wheel arch. The pin-out map is shown on the underside of the lid. In the tests in the attached document, "switch ignition ON" actually means "start engine". All doors and tailgate must be shut.

The next link below goes to a post which explains Sensor testing and also provides an attachment which is an extract of the entire AHC “Diagnostic” Section of the Factory Workshop Manual (FSM). This section applies equally to LC100 vehicles fitted with AHC and to LX470 vehicles:

Definitive list of AHC maintenance items - https://forum.ih8mud.com/threads/definitive-list-of-ahc-maintenance-items.604577/page-47#post-14378858

In the FSM "Diagnostic" extract, scroll through to Page DI-224 for Height Control Sensor details. One of the things to note here is the table on the first page of this item which describes the conditions which will result in the AHC Electronic Control Unit (ECU) recording a Diagnostic Trouble Code (DTC). Basically, this prescribes the allowable range of voltage signals (0.3 volts to 4.7 volts), and, if the actual signal from the Sensor is higher or lower than the range for the defined time and at defined speeds, then a DTC is registered.

The point is that if a DTC is recorded, then there is a Sensor problem.

The reverse is not true. If no DTC is recorded, it does not mean that all is fine with the Sensor.

For example, if the Sensor is worn or damaged – usually happens around the “N” height position where most wear occurs on the black substrate inside the Sensor cover – it is quite possible for Sensor output to be incorrect for that position but still be somewhere within the prescribed voltage range accepted by the ECU.

When that happens, there will be no DTC but there will be wrong or erratic movements of the vehicle (up or down).

For example, when “N” height is selected with a problematic Sensor, the ECU causes the Pump and the Levelling Valve operation to take place until the correct voltage signal for “N” height (~2.25 volts) is received from the Sensor in the normal way, but the vehicle will be at the wrong height at this voltage. The other aberration which occurs in this situation is that the voltage signal is translated by Techstream and will read ‘close to zero’ in inches (or millimetres) on the Techstream screen as it should, even though the vehicle is not at the correct height. These symptoms indicate a failed Sensor, regardless of whether or not a DTC is recorded.

By the way, the Sensor readings tell nothing about the condition of the 'globes'. AHC pressure readings by themselves tell nothing about the condition of the 'globes'.

The attached FSM-specified "HI/LO" test gives an indication of the overall condition of the four 'globes' taken together (not individually) by measuring the changes in fluid displaced from the 'globes' to the AHC Tank at "LO" height (which is the lowest pressure position) compared to "HI" height (which is the highest pressure position). When this test is repeated over time (say annually over a 10 year period) as the 'globes' age and slowly lose nitrogen pressure, the result declines from ~14 graduations (new 'globes') to ~7 graduations (time to replace 'globes'). To be comparable with the FSM numbers, the test needs to be done with AHC pressures within the FSM-specified ranges.

Finally, by way of general descriptive AHC information, if you have not previously seen the attached “General Description” of the AHC and TEMS systems, then it is recommended for its good explanations and diagrams,

It goes without saying but should always be said anyway: when working under the vehicle on AHC or on suspension generally, place vehicle stands under the chassis rails to ensure that there can be no movement of the vehicle body onto the human body. Accidents can and do happen, and can be avoided.
 

Attachments

  • AHC suspension precheck and damper check.pdf
    406.1 KB · Views: 25
  • AHC LC100-LX470 - General Description and Diagrams.pdf
    319.4 KB · Views: 13
  • AHC HI-LO Test per FSM.pdf
    105.1 KB · Views: 18
Last edited:

suprarx7nut

YotaMD | ADGU
Supporting Vendor
Joined
Sep 28, 2010
Messages
4,950
Location
Colorado
Website
www.YotaMD.com
The rust is cause for concern, but here's what I'd do:

1. Check for AHC codes. Do you see any trouble codes? They don't all cause the light to flash, so you have to check the stored codes in the bottom right column.
2. Assuming no codes, hook up techstream with the car on. Jack the body up slightly with a floor jack and see if the height values change as you expect. If not, replace the sensor.

Your high pressure is pretty reasonable so I don't think you're way off on pressure. I suspect either wiring or the rear sensor. The sensors are not cheap, but that's probably where I'd start. Note, do not buy anything aftermarket. Only genuine Toyota/Lexus or Aisin/Denso. Aftermarket AHC sensors are not worth the packaging they come in.
 
Last edited:
Joined
Apr 6, 2022
Messages
8
Location
Maine
Thanks for all of that @IndroCruise, that is a lot of useful info in one place and I have a lot to read. I was taking the ohm readings from the contacts where the springs sit inside the sensor, but I didn’t really know what I was doing and I don’t really trust the ohm meter I have. I will try the methods you suggested and use a different ohm meter. And yes, I am using jack stands. Good looking out.

And thanks @suprarx7nut for the additional things to try.

Rain here today and tomorrow and I have a different project taking up space in the garage, so I’ll get back on it when the weather clears and I’ll report back.
 
Joined
Apr 6, 2022
Messages
8
Location
Maine
Finally got a chance to look things over. I had to run the Active Test a couple of times because I wasn’t sure I was doing it correctly, but results were the same both times.

For the Active Test, after inserting the paper clip, turning on the car, holding “down” for 5 seconds I got the flashing lights. I ran through the steps in the box at the bottom of section 5 page 6 of the section on Active Test. This is the part where I got confused, as sometimes pressing the button combinations would cause the truck to raise/lower, while other times, nothing happened. Regardless, I ran through it a couple of times and no DTC codes appeared, and the flashing “off” light was a consistent .5 second flash throughout.

During all of that the RR Height Control Sensor row in TechStream only changed when in the H position, otherwise it was -0.5 in “N” and “Low”.

After those tests, I removed the paperclip, restarted the car, started up TechStream, jacked up the body a bit (in “N” setting), and FR Height Control Sensor and FL Height Control Sensor changed, but RR Height Control Sensor remained at -0.5.

So what do you think @suprarx7nut, replace the sensor or try some of the other things @IndroCruise suggested?
 

suprarx7nut

YotaMD | ADGU
Supporting Vendor
Joined
Sep 28, 2010
Messages
4,950
Location
Colorado
Website
www.YotaMD.com
Finally got a chance to look things over. I had to run the Active Test a couple of times because I wasn’t sure I was doing it correctly, but results were the same both times.

For the Active Test, after inserting the paper clip, turning on the car, holding “down” for 5 seconds I got the flashing lights. I ran through the steps in the box at the bottom of section 5 page 6 of the section on Active Test. This is the part where I got confused, as sometimes pressing the button combinations would cause the truck to raise/lower, while other times, nothing happened. Regardless, I ran through it a couple of times and no DTC codes appeared, and the flashing “off” light was a consistent .5 second flash throughout.

During all of that the RR Height Control Sensor row in TechStream only changed when in the H position, otherwise it was -0.5 in “N” and “Low”.

After those tests, I removed the paperclip, restarted the car, started up TechStream, jacked up the body a bit (in “N” setting), and FR Height Control Sensor and FL Height Control Sensor changed, but RR Height Control Sensor remained at -0.5.

So what do you think @suprarx7nut, replace the sensor or try some of the other things @IndroCruise suggested?
Sounds like a dead rear sensor to me. Easy first step, albeit not terribly cheap. Don't buy non Aisin or Toyota parts. Do not buy dorman or other aftermarket sensors.
 
Joined
Dec 6, 2016
Messages
705
Location
Brisbane, Australia
Finally got a chance to look things over. I had to run the Active Test a couple of times because I wasn’t sure I was doing it correctly, but results were the same both times.

For the Active Test, after inserting the paper clip, turning on the car, holding “down” for 5 seconds I got the flashing lights. I ran through the steps in the box at the bottom of section 5 page 6 of the section on Active Test. This is the part where I got confused, as sometimes pressing the button combinations would cause the truck to raise/lower, while other times, nothing happened. Regardless, I ran through it a couple of times and no DTC codes appeared, and the flashing “off” light was a consistent .5 second flash throughout.

During all of that the RR Height Control Sensor row in TechStream only changed when in the H position, otherwise it was -0.5 in “N” and “Low”.

After those tests, I removed the paperclip, restarted the car, started up TechStream, jacked up the body a bit (in “N” setting), and FR Height Control Sensor and FL Height Control Sensor changed, but RR Height Control Sensor remained at -0.5.

So what do you think @suprarx7nut, replace the sensor or try some of the other things @IndroCruise suggested?

I agree with @suprarx7nut. The vehicle symptoms and description are consistent with an erratic Rear Height Control Sensor, so that becomes a starting point. More testing is not needed per my post #10 in this thread unless you want confirmation. As explained below, replacement Front Sensors also may be in your future due to age and exposure – but maybe just do one thing at a time ….

The recommendation is strongly endorsed for replacement using only Toyota/Lexus Sensors OR Aisin Sensors for reliability and longevity. Aisin usually is better priced. Aisin supplies Sensors to Toyota/Lexus and the Aisin brand is stamped on OEM Sensors. Go figure!!)

Toyota/Lexus Height Control Sensors – Part Numbers:
89405-60012 (Front Right)
89406-60022 (Front Left)
89407-60010 (Rear)

Aisin Height Control Sensors – Part Numbers:
HST-020 (Front Right)
HST-021 (Front Left)
HST-026 (Rear)

Pricing at PartSouq Auto Parts Around the World - https://partsouq.com/ and IMPEX JAPAN — online new genuine spare parts shop - https://en.impex-jp.com/ are good places to start. Search “partsouq” and “impex” on IH8MUD for Members’ experiences with these suppliers. Then check local pricing.

There was no DTC in your description which also illustrates the fact that absence of a DTC provides no assurance that a Sensor is in correct working order.

It is worth writing out the following lengthy notes, as these may help with misunderstandings about Height Control Sensor behaviour as seen from time to time in Sensor-related posts on the IH8MUD 100 series Forum ….

Absence of Sensor DTC’s -- C1711 (front right) and/or C1712 (front left) and/or C1713 (rear) -- simply mean that the “decision rule” for the DTC was not breached because the output signals from the Height Control Sensor were within the specified upper and lower limits.

Absence of DTC does not mean that the Height Control Sensor is OK.

It means that the actual signal received by the ECU from the Sensor is wrong for some or all of the Centre Console Switch Positions (HI, N, LO). As a result the range of vertical movement of the vehicle is inconsistent. For that reason the Sensor would be judged to be faulty.

The root cause of the above might be corrosion or poor contacts (such as the spring contacts) within the Sensor or in the contacts within external connector (or harness), uneven resistance in the black carbon track inside the Sensor cover, or weakness of the tiny ‘ brushes’ which must make satisfactory contact on the carbon track, or worn ‘axle’ on which the moving parts of the Sensor pivot etc, etc.

A more serious problem which causes a short circuit or an open circuit within the Sensor almost certainly would result in a voltage signal outside the specified range and would cause a DTC to be detected.

Specifically, the FSM specifies that a Height Sensor DTC is detected ONLY:

“When the following condition is consisting and the abnormal signal continued for 1 sec. at the vehicle speed 8 km/h (5 mph) or more -- meaning that the DTC will arise when the vehicle is moving and when the ECU:

Detects an abnormal signal (Height control sensor terminal voltage of ECU is 0.3 V or less or 4.7 V or more) for every 0.01 sec. and that continued for 0.2 sec”.

If the output signal from the Height Control Sensor is within this specified voltage range of 0.3 volts to 4.7 volts, then there will be no DTC detected even if the signal is the wrong value for the height setting at the Centre Console Switch and even if the vehicle is at the wrong height.

A DTC will be detected if the ECU receives a signal outside the FSM-specified voltage range.

We know from the FSM that for each Centre Console Switch Position (HI, N, LO) the Output Signal Voltage from a healthy Sensor will be as follows when the Sensor link moves the internal brushes to arrive at the corresponding position:

HI: 4:05 volts (upper end of swing)
N: 2.25 volts (mid-swing)
LO: 0.45 volts (lower end of swig

Just to keep us all guessing, the FSM provides no method of reconciling what is happening with Sensor voltages in the AHC system – and instead Techstream gives a readout in inches or millimetres!!

We do know that at “N” height setting, the Techstream read-out should be “close to zero” inches or millimetres and the vehicle will be at whatever height the Owner has selected for “N” (using the adjusters at the Height Control Sensors).

For a vehicle which has not been ‘lifted’, the ‘standard’ IH8MUD-recommended hub-to-fender heights at “N” height would be ~19.75 inches (~500 millimetres) at the Front and ~20.5 inches (~520 millimetres) at the Rear. (Note: These heights are not FSM height specifications but they are adequate and more conveniently measured approximations and are used to match FSM-specified AHC Front and Rear pressures, subject to the weight of the vehicle).

So at “N” height, a healthy but unseen Sensor signal received by the ECU will be ~2.25 volts, and, this will correspond to Techstream readings of “close to zero” inches (or millimetres), and, vehicle heights will be 19.75 inches at the Front and 20.5 inches at the Rear (provided the vehicle has not been lifted and if the standard height adjustments have been used at the Front and Rear Sensors.

The FSM gives the following guidance on AHC height variations at HI, N and LO height settings. Variations can be expected due to the age and condition of the AHC system, condition of mechanical suspension components, suspension modifications, and the weight of the vehicle:

100 series - AHC vehicle height  variation.jpg
 
Last edited:

LndXrsr

AHC Aficionado
SILVER Star
Joined
May 3, 2020
Messages
423
Location
Cincinnati
Agree with @IndroCruise and @suprarx7nut, most likely the rear sensor started to go bad and is now fully bad based on your symptoms and Techstream reads. Your AHC system is thinking the rear is at a fairly good spot (-0.4in) in both L and N, but that number should be dynamic. Rear will be very bouncy if the system is stuck at the L ride height as the coil suspension is taking up most of the weight and the dampening is close to non-existent. There's a reason the AHC automatically raises the truck from L to N above 5mph.

Always check pressures and sensor heights going from N --> L --> N as others have mentioned.

I'd grab a new rear sensor and start there.
 
Joined
Apr 6, 2022
Messages
8
Location
Maine
Success! I swapped out the rear height sensor and everything is working great. I’ve fired up TechStream and the heights look accurate and no trouble codes. I still have to go through and adjust things to make sure the height is where it should be, but the rear no longer sags, and the ride is smooth.

Thank you everyone for your help. Thanks to @IndroCruise and @suprarx7nut for their wealth of knowledge, and willingness to share it with us here.

When I first posted, I was about 85% sure that the rear height sensor was the problem, but I wanted some additional input before spending money on an expensive part that may or may not fix the problem. I got that, and so much more. I had given very little thought to the AHC before this problem, and now I know more about it than I possibly could have expected.

Now to figure out how to handle all that rust…
 

Users who are viewing this thread

Top Bottom