The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (4 Viewers)

[dace voit]

I just finished a complete AHC service. It feels good to be done. It is not a hard job, just a bit tedious. Adjusting the heim links is a pain cuz tight space. I also replaced my tired coils in the rear.
Here are some takeaways from my experience:

-The new LC springs reduced the rear pressure by about .6, bringing in to the middle of the spectrum. It has always been a little high so it’s nice to see it in range.
-adjusting the heim links is a bit of a pain because tight in there. One thing I noticed that I didn’t see anywhere is that the wheels must be straight when adjusting. I tried adjusting with the wheels turned for some room but it affects the measurement quite a bit. Also, it’s nearly impossible to get the sensors to stay at 0.0. I would adjust and check and then change height and the readings would change. I ended up setting to 0.0 but still read -0.2. IMHO it’s not really worth it to fool with that too much. Having a helper to watch the readings as you adjust is nice.
-When flushing, I did not flush the left side in L height as the first post lists. I felt that having in N pushed more fluid out from that side. When I flushed the right side, the fluid ran clean pretty quickly because of this I think. I ended up using a full 2.5L can plus a .5L bottle. I could have gotten away with just the can as my fluid at 60k was not bad. The extra was nice though.
-I went the “putz” route and used spring compressors for the LH coil spring. Not that it was better, I just didn’t want to disconnect anything else. In hindsight, disconnecting the brake line bracket and diff breather may have been faster. YMMV on what you choose to do.
-I didn’t need a jack to push the axle down for the RH spring. I just pushed with my hand. Easy.
-All in all, this is not a hard job to do and really worth the effort. My truck still was riding nicely as it’s been maintained but was starting to get a bit rough in the ride. Now, the magic carpet is back!
-One thing I’m not sure about is the rear height measurement. My left is 1/2” lower than the right. Since cross-leveling is done only for the front(from what I can tell), I’m not sure how this is addressed. Any input is appreciated. I probably missed something.
-Unplugging the temp sensor did NOT help on my 2006 LC. In fact, it caused some erratic behavior and readings. Plugging in the sensor brought things back to normal.
-Lastly, it was cool to see things come together as I finalized the pressure adjustments. It was a bit wonky at first because the t-bars were about 4 turns too tight. But as I kept adjusting, things got better and better. Moral of the story: Keep at it. You will be rewarded!

 

[baltistyle]

I just finished a complete AHC service. It feels good to be done. It is not a hard job, just a bit tedious. Adjusting the heim links is a pain cuz tight space. I also replaced my tired coils in the rear.
Here are some takeaways from my experience:

-The new LC springs reduced the rear pressure by about .6, bringing in to the middle of the spectrum. It has always been a little high so it’s nice to see it in range.
-adjusting the heim links is a bit of a pain because tight in there. One thing I noticed that I didn’t see anywhere is that the wheels must be straight when adjusting. I tried adjusting with the wheels turned for some room but it affects the measurement quite a bit. Also, it’s nearly impossible to get the sensors to stay at 0.0. I would adjust and check and then change height and the readings would change. I ended up setting to 0.0 but still read -0.2. IMHO it’s not really worth it to fool with that too much. Having a helper to watch the readings as you adjust is nice.
-When flushing, I did not flush the left side in L height as the first post lists. I felt that having in N pushed more fluid out from that side. When I flushed the right side, the fluid ran clean pretty quickly because of this I think. I ended up using a full 2.5L can plus a .5L bottle. I could have gotten away with just the can as my fluid at 60k was not bad. The extra was nice though.
-I went the “putz” route and used spring compressors for the LH coil spring. Not that it was better, I just didn’t want to disconnect anything else. In hindsight, disconnecting the brake line bracket and diff breather may have been faster. YMMV on what you choose to do.
-I didn’t need a jack to push the axle down for the RH spring. I just pushed with my hand. Easy.
-All in all, this is not a hard job to do and really worth the effort. My truck still was riding nicely as it’s been maintained but was starting to get a bit rough in the ride. Now, the magic carpet is back!
-One thing I’m not sure about is the rear height measurement. My left is 1/2” lower than the right. Since cross-leveling is done only for the front(from what I can tell), I’m not sure how this is addressed. Any input is appreciated. I probably missed something.
-Unplugging the temp sensor did NOT help on my 2006 LC. In fact, it caused some erratic behavior and readings. Plugging in the sensor brought things back to normal.
-Lastly, it was cool to see things come together as I finalized the pressure adjustments. It was a bit wonky at first because the t-bars were about 4 turns too tight. But as I kept adjusting, things got better and better. Moral of the story: Keep at it. You will be rewarded!

Per your left and right rear discrepancy, did you place the new springs on the correct sides? I also did lc springs on my lx and one spring is slightly longer to account for driver/gas tank. If the front is not leaning, the rear should not either, having recently done all this stuff.

 

[dace voit]

Per your left and right rear discrepancy, did you place the new springs on the correct sides? I also did lc springs on my lx and one spring is slightly longer to account for driver/gas tank. If the front is not leaning, the rear should not either, having recently done all this stuff.

I did. Setting the new springs next to each other, they looked very similar in length. I didn’t actually measure though. I triple checked the numbers, and matched the colors with the old springs. Everything checked out.

 

[IndroCruise]

I just finished a complete AHC service. It feels good to be done. It is not a hard job, just a bit tedious. Adjusting the heim links is a pain cuz tight space. I also replaced my tired coils in the rear.
Here are some takeaways from my experience:

-The new LC springs reduced the rear pressure by about .6, bringing in to the middle of the spectrum. It has always been a little high so it’s nice to see it in range.
-adjusting the heim links is a bit of a pain because tight in there. One thing I noticed that I didn’t see anywhere is that the wheels must be straight when adjusting. I tried adjusting with the wheels turned for some room but it affects the measurement quite a bit. Also, it’s nearly impossible to get the sensors to stay at 0.0. I would adjust and check and then change height and the readings would change. I ended up setting to 0.0 but still read -0.2. IMHO it’s not really worth it to fool with that too much. Having a helper to watch the readings as you adjust is nice.
-When flushing, I did not flush the left side in L height as the first post lists. I felt that having in N pushed more fluid out from that side. When I flushed the right side, the fluid ran clean pretty quickly because of this I think. I ended up using a full 2.5L can plus a .5L bottle. I could have gotten away with just the can as my fluid at 60k was not bad. The extra was nice though.
-I went the “putz” route and used spring compressors for the LH coil spring. Not that it was better, I just didn’t want to disconnect anything else. In hindsight, disconnecting the brake line bracket and diff breather may have been faster. YMMV on what you choose to do.
-I didn’t need a jack to push the axle down for the RH spring. I just pushed with my hand. Easy.
-All in all, this is not a hard job to do and really worth the effort. My truck still was riding nicely as it’s been maintained but was starting to get a bit rough in the ride. Now, the magic carpet is back!
-One thing I’m not sure about is the rear height measurement. My left is 1/2” lower than the right. Since cross-leveling is done only for the front(from what I can tell), I’m not sure how this is addressed. Any input is appreciated. I probably missed something.
-Unplugging the temp sensor did NOT help on my 2006 LC. In fact, it caused some erratic behavior and readings. Plugging in the sensor brought things back to normal.
-Lastly, it was cool to see things come together as I finalized the pressure adjustments. It was a bit wonky at first because the t-bars were about 4 turns too tight. But as I kept adjusting, things got better and better. Moral of the story: Keep at it. You will be rewarded!

Great to read a success story!!!

Reflecting on the observation:

"One thing I’m not sure about is the rear height measurement. My left is 1/2” lower than the right. Since cross-leveling is done only for the front(from what I can tell), I’m not sure how this is addressed. Any input is appreciated. I probably missed something".

This has come up a few times and it is entirely possible that each case is different. I wrote some notes a while back and maybe the post linked below contains some useful suggestions:

Props to PADDO's AHC fluid replacement method! - https://forum.ih8mud.com/threads/props-to-paddos-ahc-fluid-replacement-method.925459/page-10#post-14071202

The essential point is to beware of "pursuit of perfection". As a starter, the FSM gives a tolerance on Front 'cross-levelling' of +/- 0.39 inches (or +/- 10 millimetres) -- see attachment at the mentioned post -- so it would be unsurprising to find something similar at the Rear.

Even if the vehicle was absolutely and exactly perfect in all dimensional respects when it left the factory (not likely, there always are manufacturing tolerances), then inevitably there will be some accumulating differences in side to side wear and tear in mechanical suspension components, such as control arms front and rear, ball-joints, load-bearing bushes everywhere, bearings, panhard at rear, etc, etc, etc, after 16 years of life on 2006 vehicle. The body shell may not be sitting exactly the same side to side on the cushions between the body and the chassis, especially if there has been some accident body damage in the vehicle history. The hub-to-fender measurements (and even fender-to-floor measurements) are only approximations of the more precise but fiddly FSM height measurement method. Some minor chassis twist is possible as a result of wear and tear -- and even at the factory, no two chassis's will be exactly the same despite precision jigs used in manufacturing, there will be tolerances. So all things considered, the vehicle may not sit perfectly and yet still be free of faults.

That said, there a few things worth checking -- a few other thoughts and a checklist are suggested in the post at the above link.

 

[dace voit]

Even if the vehicle was absolutely and exactly perfect in all dimensional respects when it left the factory (not likely, there always are manufacturing tolerances), then inevitably there will be some accumulating differences in side to side wear and tear in mechanical suspension components, such as control arms front and rear, ball-joints, load-bearing bushes everywhere, bearings, panhard at rear, etc, etc, etc, after 16 years of life on 2006 vehicle. The body shell may not be sitting exactly the same side to side on the cushions between the body and the chassis, especially if there has been some accident body damage in the vehicle history. The hub-to-fender measurements (and even fender-to-floor measurements) are only approximations of the more precise but fiddly FSM height measurement method. Some minor chassis twist is possible as a result of wear and tear -- and even at the factory, no two chassis's will be exactly the same despite precision jigs used in manufacturing, there will be tolerances. So all things considered, the vehicle may not sit perfectly and yet still be free of faults.

Thanks for the input!
You did forget the accumulating difference of whether it has ever left the ground or not.

 

[2001LC]

I just finished a complete AHC service. It feels good to be done. It is not a hard job, just a bit tedious. Adjusting the heim links is a pain cuz tight space. I also replaced my tired coils in the rear.
Here are some takeaways from my experience:

-The new LC springs reduced the rear pressure by about .6, bringing in to the middle of the spectrum. It has always been a little high so it’s nice to see it in range.
-adjusting the heim links is a bit of a pain because tight in there. One thing I noticed that I didn’t see anywhere is that the wheels must be straight when adjusting. I tried adjusting with the wheels turned for some room but it affects the measurement quite a bit. Also, it’s nearly impossible to get the sensors to stay at 0.0. I would adjust and check and then change height and the readings would change. I ended up setting to 0.0 but still read -0.2. IMHO it’s not really worth it to fool with that too much. Having a helper to watch the readings as you adjust is nice.
-When flushing, I did not flush the left side in L height as the first post lists. I felt that having in N pushed more fluid out from that side. When I flushed the right side, the fluid ran clean pretty quickly because of this I think. I ended up using a full 2.5L can plus a .5L bottle. I could have gotten away with just the can as my fluid at 60k was not bad. The extra was nice though.
-I went the “putz” route and used spring compressors for the LH coil spring. Not that it was better, I just didn’t want to disconnect anything else. In hindsight, disconnecting the brake line bracket and diff breather may have been faster. YMMV on what you choose to do.
-I didn’t need a jack to push the axle down for the RH spring. I just pushed with my hand. Easy.
-All in all, this is not a hard job to do and really worth the effort. My truck still was riding nicely as it’s been maintained but was starting to get a bit rough in the ride. Now, the magic carpet is back!
-One thing I’m not sure about is the rear height measurement. My left is 1/2” lower than the right. Since cross-leveling is done only for the front(from what I can tell), I’m not sure how this is addressed. Any input is appreciated. I probably missed something.
-Unplugging the temp sensor did NOT help on my 2006 LC. In fact, it caused some erratic behavior and readings. Plugging in the sensor brought things back to normal.
-Lastly, it was cool to see things come together as I finalized the pressure adjustments. It was a bit wonky at first because the t-bars were about 4 turns too tight. But as I kept adjusting, things got better and better. Moral of the story: Keep at it. You will be rewarded!

"-I went the “putz” route and used spring compressors for the LH coil spring. Not that it was better, I just didn’t want to disconnect anything else. In hindsight, disconnecting the brake line bracket and diff breather may have been faster. YMMV on what you choose to do.
-I didn’t need a jack to push the axle down for the RH spring. I just pushed with my hand. "

When adding 30 spacer, with or without new AHC coils. I use spring compressor on LR always. BTW: The spacers drop pressure in rear just a tad more, they do not add to lift on AHC OEM coils.

"adjusting the heim links is a bit of a pain because tight in there. One thing I noticed that I didn’t see anywhere is that the wheels must be straight when adjusting. I tried adjusting with the wheels turned for some room but it affects the measurement quite a bit."

The sensor arms almost never need adjusting on a stock rig, if they've never been touched. I consistently get 19 3/16" front and 19 15/16" rear after cross level with senors untouched, and no mod (all factory) tire PSI set at factory spec, full tank. I measure to within ~1/64".

I do adjust sensors, for a few reasons. Mostly when modifying a rig for either sensor lift, King coils & spacers, and or LC T-bars for greater weight handling. When I do adjust sensors. I adjust rear first, once cross leveled with T-bars. I adjust rear to bring pressure into my target goal. Then adjust front senors to get my target height (rake). I do turn tires, to adjusting of the arms. Just to little room to work easily unless I do. I do this with AHC in H engine off. I use measuring sticks and caliper to work at getting both sensor set the same (mirror). I then remeasure heights and check pressure, after short drive.

A new service I do is lubing (moly grease) the balls of the heim links. I've a bucket full of old frozen ones. Thy freeze and can damage the arm, sensor and bracket. I use a needle tip on my grease gun. I do not pierce the boots, just come up under it from center and inject the grease under boot. All sensor arms ball joints will freeze up sooner or later. Lubing is just buying time, until replaced.

"My left is 1/2” lower than the right"
I have only found 2 reason for this, in the dozens and dozens I've adjusted.
1) Body and or frame bent/damage, from accident (even minor fender or bumper hits) or catching air over the bumps.
2) Measurement not accurate.

If I get a rear measurement not equal, and no sign of accident. I remeasure. It is the rear I use, to confirm I'm cross level in front.

To help me keep measurements consistently accurate, when using short-cut/simplified fenders technique of measuring:

Fronts) I place a dot, measured to dead center of grease cap. I use same tape measures, and make sure I "push up" (slide on it's rivet) on tape measure, and measure at 90 degrees angle from fender down to cap. This becomes very difficult with over-sized tires and or wheel spacers. Which may keep tape measure from hang freely straight down at 90 deg.

Rears) I use the chrome bar from tool bag. I place the bar in the center of axle. I place a magnet level on the chrome bar. Then measure down to the level on bar. Rear fender has a double lip, which changes measure by about 1/4". I always measure from outer lip. I use level/bar in front, if tires/spacers are pushing out the tape measure.


Additionally: Very important to drive, before final adjustment. More so if was on jack/jack stand for any reason. Measurements and pressure will change.

 

[dace voit]

When adding 30 spacer, with or without new AHC coils. I use spring compressor on LR always. BTW: The spacers drop pressure in rear just a tad more, they do not add to lift on AHC OEM coils.

The "putz" comment, I couldn't resist because of the snarky post I read. Hardly putzy at all really. Anyway, I'm happy that the new spring brought me to where I want to be consider the age of the rest of the system.

The sensor arms almost never need adjusting on a stock rig, if they've never been touched. I consistently get 19 3/16" front and 19 15/16" rear after cross level with senors untouched, and no mod (all factory) tire PSI set at factory spec, full tank. I measure to within ~1/64".

I couldn't leave well enough alone. Having never messed with them, I couldn't resist. They were fine before I started.

A new service I do is lubing (moly grease) the balls of the heim links. I've a bucket full of old frozen ones. Thy freeze and can damage the arm, sensor and bracket. I use a needle tip on my grease gun. I do not pierce the boots, just come up under it from center and inject the grease under boot. All sensor arms ball joints will freeze up sooner or later. Lubing is just buying time, until replaced.

Not a bad idea. Mine are all fine, not stiff at all. But considering what is put on the roads up here in the mountains and that I live a mile back a dirt(sometimes mud) road, lubing can def help.

If I get a rear measurement not equal, and no sign of accident. I remeasure. It is the rear I use, to confirm I'm cross level in front.

Interesting consideration using the rears to confirm the front. Considering the inconsistencies that exist in measuring, it would be nice to have a more accurate way to go about this. That said, the minor differences will not be noticed by most people.

 

[2001LC]

Interesting consideration using the rears to confirm the front. Considering the inconsistencies that exist in measuring, it would be nice to have a more accurate way to go about this. That said, the minor differences will not be noticed by most people.

Yeah if not cross level in front, rears will not be cross level either.

There is a way to measure height of vehicle, which a bent body or old body mounts will not effect! It's in the FSM. Which has us measure points from ground up to spindle frt /axle rear & control arms. But to get measurement, is difficult. So @PADDO (IIRC) came up with this simple easy method, of axle to fender.

The FSM requires height be checked and adjusted, before alignment.

 

[IndroCruise]

Yeah if not cross level in front, rears will not be cross level either.

There is a way to measure height of vehicle, which a bent body or old body mounts will not effect! It's in the FSM. Which has us measure points from ground up to spindle frt /axle rear & control arms. But to get measurement, is difficult. So @PADDO (IIRC) came up with this simple easy method, of axle to fender.

The FSM requires height be checked and adjusted, before alignment.

@2001LC has summarised the situation and the history. Just to get a bit OCD about this, here are some details about FSM-specified, AHC-equipped LC100 height measurements for others whose searches may lead them here.

Re-capping AHC adjustments: Always on level ground, no people and no loads in vehicle, fuel full, steering straight ahead, the sequence always is:

1. 'Cross-level' using Torsion Bar adjusters and a tape-measure (and not Height Control Sensor adjusters) -- aim to equalise per FSM, actual measurements are unimportant at this stage,
2. Set Front and Rear physical heights with a tape-measure -- cannot use Torsion Bar adjusters -- suggest use 'Active Test' or use jacks and stands to hold vehicle at desired Front and Rear heights or use some other safe arrangement,
3. When physical heights are correct, with vehicle at "N" height AND WITH ENGINE "OFF" TO PREVENT AHC MOVEMENT AND WITH STANDS IN PLACE UNDER CHASSIS TO PROHIBIT ANY ACCIDENTAL MOVEMENT OF VEHICLE BODY ONTO HUMAN BODY and with only ignition switch "ON" (engine NOT started) and AHC "ON", adjust Height Control Sensor readings to near as possible to zero at "N" height, using Techstream or other AHC-readable scanner,
4. When physical heights are correct and auto-levelling response is correct and stable (Height Control Sensors reading near zero on Techstream or scanner) at "N" height, use Torsion Bar adjusters and Techstream or other AHC-readable scanner to adjust Front AHC pressures within FSM-specified range. [Note: Bringing Rear AHC pressures into FSM-specified range may require spacers or spring replacement (or spring upgrade for a heavy vehicle)],
5. Re-check all measurements and settings after test drive,
6. When physical heights and Front and Rear AHC pressures are correct, check overall ' globe' condition by observing difference in AHC Fluid level between "LO" height setting and "HI" height setting (14 graduations = near new; 7 graduations = change out all ' globes').

AHC height measurements -- from LC100 FSM (also see attachments):

See also:

Measure AHC neutral pressure? - https://forum.ih8mud.com/threads/measure-ahc-neutral-pressure.529309/page-2#post-12133764

Late edit:

Here is a bit more history ….

@PADDO – July 22, 2016:
Adjusting torsion bar to level front side to side, with AHC - https://forum.ih8mud.com/threads/adjusting-torsion-bar-to-level-front-side-to-side-with-ahc.940218/#post-10482579

@PADDO – September 14, 2015 – commenting on the hub-to-fender approximations compared to FSM:
Definitive list of AHC maintenance items - https://forum.ih8mud.com/threads/definitive-list-of-ahc-maintenance-items.604577/page-14#post-9938197

@PADDO – January 22, 2016 – attaches an extract from a 2003 LX470 FSM. This shows miniscule differences to the LC100 pic and LC100 attachments in my post #289 above. The differences are: Front: 0.012 inch (or 0.3 millimetres); Rear: 0.008 inch (or 0.2 millimetres) -- certainly much too small to worry about!
AHC 1/2" in rear? - https://forum.ih8mud.com/threads/ahc-1-2-in-rear.904684/#post-10152318

Conclusion: For physical height measurements on AHC-equipped vehicles, stay with the easy-to-measure hub-to-fender approximations as recommended years ago by @PADDO and generally adopted within IH8MUD:

Front: 19.75 inches (or 500 millimetres);
Rear: 20.50 inches (or 520 millimetres)

These are the numbers for a stock vehicle and are independent of tyre size. The numbers will be different after a ‘sensor lift’ but still independent of tyre size.

 

[2001LC]

@2001LC has summarised the situation and the history. Just to get a bit OCD about this, here are some details about FSM-specified, AHC-equipped LC100 height measurements for others whose searches may lead them here.

Re-capping AHC adjustments: Always on level ground, no people and no loads in vehicle, fuel full, steering straight ahead, the sequence always is:

1. 'Cross-level' using Torsion Bar adjusters and a tape-measure (and not Height Control Sensor adjusters) -- aim to equalise per FSM, actual measurements are unimportant at this stage,
2. Set Front and Rear physical heights with a tape-measure -- cannot use Torsion Bar adjusters -- suggest use 'Active Test' or use jacks and stands to hold vehicle at desired Front and Rear heights or use some other safe arrangement,
3. When physical heights are correct, with vehicle at "N" height AND WITH ENGINE "OFF" TO PREVENT AHC MOVEMENT AND WITH STANDS IN PLACE UNDER CHASSIS TO PROHIBIT ANY ACCIDENTAL MOVEMENT OF VEHICLE BODY ONTO HUMAN BODY and with only ignition switch "ON" (engine NOT started) and AHC "ON", adjust Height Control Sensor readings to near as possible to zero at "N" height, using Techstream or other AHC-readable scanner,
4. When physical heights are correct and auto-levelling response is correct and stable (Height Control Sensors reading near zero on Techstream or scanner) at "N" height, use Torsion Bar adjusters and Techstream or other AHC-readable scanner to adjust Front AHC pressures within FSM-specified range. [Note: Bringing Rear AHC pressures into FSM-specified range may require spacers or spring replacement (or spring upgrade for a heavy vehicle)],
5. Re-check all measurements and settings after test drive,
6. When physical heights and Front and Rear AHC pressures are correct, check overall ' globe' condition by observing difference in AHC Fluid level between "LO" height setting and "HI" height setting (14 graduations = near new; 7 graduations = change our all ' globes').

AHC height measurements -- from LC100 FSM (also see attachments):

View attachment 3062920
See also:

Measure AHC neutral pressure? - https://forum.ih8mud.com/threads/measure-ahc-neutral-pressure.529309/page-2#post-12133764

Late edit:

Here is a bit more history ….

@PADDO – July 22, 2016:
Adjusting torsion bar to level front side to side, with AHC - https://forum.ih8mud.com/threads/adjusting-torsion-bar-to-level-front-side-to-side-with-ahc.940218/#post-10482579

@PADDO – September 14, 2015 – commenting on the hub-to-fender approximations compared to FSM:
Definitive list of AHC maintenance items - https://forum.ih8mud.com/threads/definitive-list-of-ahc-maintenance-items.604577/page-14#post-9938197

@PADDO – January 22, 2016 – attaches an extract from a 2003 LX470 FSM. This shows miniscule differences to the LC100 pic and LC100 attachments in this post #289 in this thread. The differences are: Front: 0.012 inch (or 0.3 millimetres); Rear: 0.008 inch (or 0.2 millimetres) -- certainly much too small to worry about!
AHC 1/2" in rear? - https://forum.ih8mud.com/threads/ahc-1-2-in-rear.904684/#post-10152318

Conclusion: For physical height measurements on AHC-equipped vehicles, stay with the easy-to-measure hub-to-fender approximations as recommended years ago by @PADDO and generally adopted within IH8MUD:

Front: 19.75 inches (or 500 millimetres);
Rear: 20.50 inches (or 520 millimetres)

These are the numbers for a stock vehicle and are independent of tyre size. The numbers will be different after a ‘sensor lift’ but still independent of tyre size.

A few thoughts on heights:

The only thing I've found different over the years. Is measurement (inches) when using the @PADDO method axle to fender. I've got a mark on my tape measure at just over 19 3/16. Factory stock (tire 29 PSI frt, 32 psi rear, full tank of gas, 3rd row in), AHC flushed & tuned . I always find fronts, right about 19 3/16"+ once cross leveled.

When I first started tuning AHC. I found myself adjusting height sensors to get `19 3/4" frt & 20 1/2" rear. As I was always finding them at a lower measurement of~19 1/4" -+ 1/16 frt and 20 1/8" rear. Not the 19 3/4" & 20 1/2"everyone uses. I realized after doing many factory stock rigs, some with as low as 50K others as high as 370K miles, in all years, some new Globes. One day (time & tools) I should use factory method, and see what the cheat height measurement comes in at.

Today for factory height set-up I use 19 3/16" front. Which means I rarely adjust sensor on a simple flush and T-bar adjust. I'm only adjusting height sensors during modified setups, damaged sensors or sensor replacement. Even when I install new OEM LC coils and 30mm spacers. I don't adjust height sensors, unless they've been moved, adjusted or bent as a rule.

When doing a sensor lift with LC T-bars, Kings AHC coils and 30MM spacer. I base front height, on what rear comes in at, once rear maxed sensor lifted. Using Kings and 30MM spacer, and max rear sensor arm to top of slide. I'm finding 30mm spacer is a little to thick. I can't get pressure lower than ~4.7Mpa in rear. Height comes in at 21", so I set front at 20" to 20 1/4. We're seeing how 4.7Mpa in rear feels for now. We may increase rear pressure to 5.6Mpa. Either by reducing spacer to a 20 or 10mm. Or thinking about modifying the height sensor arm, to give anther 1/8" to 1/4" sensor lift rear.

 

[TreatSmash]

Real quick, if my LC is leaning to the right and is lower on both front and rear wheel, can that be fixed with torsion bar alone or does it require a rear spacer as well?

 

[IndroCruise]

Real quick, if my LC is leaning to the right and is lower on both front and rear wheel, can that be fixed with torsion bar alone or does it require a rear spacer as well?

Real quick – if RH Front is low, theoretically in a perfect stock vehicle with a straight, stiff chassis, there should be no effect on RH Rear, but LH Rear should be high.

If RH Front is low AND RH Rear is low, and Front has been cross-levelled per attached FSM extract on level ground (meaning non-sloping concrete garage floor or similar, not street), then something else is happening. Suggest check:

• Even distribution of weight in or on vehicle,
• Incorrectly fitted rear springs,
• Damaged rear spring(s),
• Wheels and tyres – same type, same diameter, same wear, same inflation pressure (so rolling radius is the same all round),
• All shock absorber bushes – remembering that in an AHC vehicle the ‘shock absorbers’ are hydraulic struts which carry part of the vehicle weight, so unevenly worn or collapsed bushes at ‘shock absorbers’ will affect the way the vehicle sits on level ground,
• Condition of Front upper and lower control arms – not bent or damaged,
• All Front upper and lower control arm bushes,
• All Torsion bar attachments to Front lower control arms,
• All wheel bearings and adjustments,
• All Rear spring seats,
• Accident damage or disintegrated cushions or rust -- affecting the way the body shell sits on the chassis,
• Any vehicle history or underbody indications that suggest some possible cause capable of twisting the chassis itself,
• Anything else a vehicle repair shop or wheel alignment shop might suggest,
• Late edit: Problem in AHC Control Valve Assembly eg stuck Gate Valve preventing Right-Left Rear AHC pressure equalisation -- possible but seems unlikely.

In all of this beware of ‘pursuit of perfection’. There will be some variations (within tolerance) on the day the vehicle left the factory. Wear-and-tear over the following 16 years will have added further variations.

Suggest identify the actual cause – adding a spacer might just disguise some other problem.

Anyway, suggest start with Front cross-level, then decide on next steps, including spacer or not ....

 

[TreatSmash]

Real quick – if RH Front is low, theoretically in a perfect stock vehicle with a straight, stiff chassis, there should be no effect on RH Rear, but LH Rear should be high.

If RH Front is low AND RH Rear is low, and Front has been cross-levelled per attached FSM extract on level ground (meaning non-sloping concrete garage floor or similar, not street), then something else is happening. Suggest check:

• Even distribution of weight in or on vehicle,
• Incorrectly fitted rear springs,
• Damaged rear spring(s),
• Wheels and tyres – same type, same diameter, same wear, same inflation pressure (so rolling radius is the same all round),
• All shock absorber bushes – remembering that in an AHC vehicle the ‘shock absorbers’ are hydraulic struts which carry part of the vehicle weight, so unevenly worn or collapsed bushes at ‘shock absorbers’ will affect the way the vehicle sits on level ground,
• Condition of Front upper and lower control arms – not bent or damaged,
• All Front upper and lower control arm bushes,
• All Torsion bar attachments to Front lower control arms,
• All wheel bearings and adjustments,
• All Rear spring seats,
• Accident damage or disintegrated cushions or rust -- affecting the way the body shell sits on the chassis,
• Any vehicle history or underbody indications that suggest some possible cause capable of twisting the chassis itself,
• Anything else a vehicle repair shop or wheel alignment shop might suggest.

In all of this beware of ‘pursuit of perfection’. There will be some variations (within tolerance) on the day the vehicle left the factory. Wear-and-tear over the following 16 years will have added further variations.

Suggest identify the actual cause – adding a spacer might just disguise some other problem.

Anyway, suggest start with Front cross-level, then decide on next steps, including spacer or not ....

Thank you. I will learn someday. There's no such thing as "real quick."

Of course I was reading through this because I'm having problems with my AHC and in the course of inspecting my vehicle and going through these documents, I determined that my RH front and RH rear are 1 inch lower then LH. Which is something I had suspected for a while just by looking at it.

So now I'm kind of wondering which one should get my attention first?

The suspension actually works fine, it's just that my AHC won't go up or down. Unless I reset it using the jumper under the hood method.

I just ordered the code reader though so I'm going to hold off and get some codes and pressures information before I start asking for help.

 

[IndroCruise]

Thank you. I will learn someday. There's no such thing as "real quick."

Of course I was reading through this because I'm having problems with my AHC and in the course of inspecting my vehicle and going through these documents, I determined that my RH front and RH rear are 1 inch lower then LH. Which is something I had suspected for a while just by looking at it.

So now I'm kind of wondering which one should get my attention first?

The suspension actually works fine, it's just that my AHC won't go up or down. Unless I reset it using the jumper under the hood method.

I just ordered the code reader though so I'm going to hold off and get some codes and pressures information before I start asking for help.

Yes -- Techstream or other scanner which reads Suspension Electronic Control Unit would be good. See also Late Edit I just added to my previous post.

 

[IndroCruise]

Yes -- Techstream or other scanner which reads Suspension Electronic Control Unit would be good. See also Late Edit I just added to my previous post.

It is a helpful fact that you can raise and lower the vehicle with the “Height Control Operation Test” a.k.a. “Active Test” per Section 5 at Page 6 of the attachment below. It means that lots of things appear to be working – including

• the AHC Pump,
• the various AHC-related fuses (found in the Junction Boxes in the engine bay and behind the kick-panel forward of the LH Front door),
• the AHC Pump Relay (also found in the Junction Box in the engine bay),
• the AHC Main Relay (located under the dash with the Suspension Control ECU),
• the AHC control switch on the centre console.

It is worth running through the “Input Signal Check” a.k.a. “Test Mode Check” per Section 2 at Page 2 of the attachment to see if that reveals problems with various other inputs to the Suspension Control ECU.

(Special Service Tool SST 09843-18020 is a simple connector used to bridge between the prescribed terminals, using DLC1 in the engine bay in this method. An unbent paper-clip is just as good! A similar method using DLC3 under the dash can be found in many versions of the Factory Service Manual. The method using DLC1 performs in the same way – it is just a bit easier to manage than positioning connectors to the correct terminals under the dash).

It is also worth having a look at the “Problems Symptoms Table” at Page DI-221 at this Factory Service Manual (FSM) reference:

AHC Diagnostics:
LC100 Workshop Manual - https://lc100e.github.io/
Then follow tabs in index panel at RHS of opening page:
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL & SKYHOOK TEMS

Also in this section of the FSM, the AHC circuits are listed by Diagnostic Trouble Codes (DTC’s), starting with C1711 through to C1713 which relates to Height Control Sensors. It is a worth a look through the whole list to see in which circuits a malfunction may cause a “fail safe function” which prevents or restricts operation of the Active Height Control (AHC) system or the Toyota Electronic Modular Suspension (TEMS) system, or both. There are some different effects, slightly different “fail safe fundtions”, with the fault conditions on various different circuits and components. In each case, a table is shown which defines the circumstances which give rise to the relevant DTC.

The DTC definitions in the table are exact (although sometimes not well expressed) -- and this sometimes requires interpretation and comparison with what the vehicle actually is doing on the ground. For example, in the case of the Height Control Sensors, DTC C1711 through to DTC C1713 appear only if the Sensor output voltage is outside the FSM-specified range, either too high or too low. It can and does happen that a degraded Sensor (wear and tear, corrosion, whatever) sends a signal that is within the FSM-specified voltage range but is the wrong voltage for the height of the vehicle, due to a defective Sensor. In this situation, a DTC may not appear, even though the Sensor is defective. The vehicle may show strange behaviours – such as Front and Rear being at different heights, or obviously incorrect Height Sensor readings on Techstream or other scanner. In such cases, it is best to remove Sensors, disassemble, clean, test per FSM, reinstall if satisfactory, but if in doubt due to condition or age, replace these 'wear items' with genuine OEM parts, either Toyota/Lexus or Aisin, not substitutes.

Moral of the story: a DTC indicates a problem or defect in the relevant circuit (meaning component plus connector plus harness) -- but absence of a DTC does not necessarily mean that all is well. This is especially the case with Height Control Sensors.

Nevertheless, Techstream or other suitable scanner is a vital tool. It is almost impossible to manage and maintain the AHC and TEMS systems without being able to read and interpret the Suspension Control ECU.

 

[TreatSmash]

It is a helpful fact that you can raise and lower the vehicle with the “Height Control Operation Test” a.k.a. “Active Test” per Section 5 at Page 6 of the attachment below. It means that lots of things appear to be working – including

• the AHC Pump,
• the various AHC-related fuses (found in the Junction Boxes in the engine bay and behind the kick-panel forward of the LH Front door),
• the AHC Pump Relay (also found in the Junction Box in the engine bay),
• the AHC Main Relay (located under the dash with the Suspension Control ECU),
• the AHC control switch on the centre console.

It is worth running through the “Input Signal Check” a.k.a. “Test Mode Check” per Section 2 at Page 2 of the attachment to see if that reveals problems with various other inputs to the Suspension Control ECU.

(Special Service Tool SST 09843-18020 is a simple connector used to bridge between the prescribed terminals, using DLC1 in the engine bay in this method. An unbent paper-clip is just as good! A similar method using DLC3 under the dash can be found in many versions of the Factory Service Manual. The method using DLC1 performs in the same way – it is just a bit easier to manage than positioning connectors to the correct terminals under the dash).

It is also worth having a look at the “Problems Symptoms Table” at Page DI-221 at this Factory Service Manual (FSM) reference:

AHC Diagnostics:
LC100 Workshop Manual - https://lc100e.github.io/
Then follow tabs in index panel at RHS of opening page:
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL & SKYHOOK TEMS

Also in this section of the FSM, the AHC circuits are listed by Diagnostic Trouble Codes (DTC’s), starting with C1711 through to C1713 which relates to Height Control Sensors. It is a worth a look through the whole list to see in which circuits a malfunction may cause a “fail safe function” which prevents or restricts operation of the Active Height Control (AHC) system or the Toyota Electronic Modular Suspension (TEMS) system, or both. There are some different effects, slightly different “fail safe fundtions”, with the fault conditions on various different circuits and components. In each case, a table is shown which defines the circumstances which give rise to the relevant DTC.

The DTC definitions in the table are exact (although sometimes not well expressed) -- and this sometimes requires interpretation and comparison with what the vehicle actually is doing on the ground. For example, in the case of the Height Control Sensors, DTC C1711 through to DTC C1713 appear only if the Sensor output voltage is outside the FSM-specified range, either to high or to low. It can and does happen that a degraded Sensor (wear and tear, corrosion, whatever) sends a signal that is within the FSM-specified voltage range but is the wrong voltage for the height of the vehicle, due to a defective Sensor. In this situation, a DTC may not appear, even though the Sensor is defective. The vehicle may show strange behaviours – such as Front and Rear being at different heights, or obviously incorrect Height Sensor readings on Techstream or other sacnner.

Moral of the story: a DTC indicates a problem or defect in the relevant circuit (meaning component plus connector plus harness) but absence of a DTC does not necessarily mean that all is well. This is especially the case with Height Control Sensors.

Nevertheless, Techstream or other suitable scanner is a vital tool. It is almost impossible to manage and maintain the AHC and TEMS systems without being able to read and interpret the Suspension Control ECU.

Thanks for writing this up.

I actually already know that all of those components work because when I reset my AHC it works fine. And I get eight or nine graduations.

I reset it using a paper clip with the DLC1 box. It just seems to be shorting or something. Because it will only stay operational for a day or two after I reset it. It just stays at normal height and won't go up or down.

I don't want to get too deep into the woods now, but once I get my code reader in hand and read through what you've given me, I'll come back with some questions most likely. But I don't want to get started until I have the tools I need to provide The needed troubleshooting information.

 

[TreatSmash]

Update I got my OBDLinkMX+ and got it working.

Trouble code for my AHC is the speed sensor, which if I had to guess is related to the fact that the speed sensor wire in my dashboard has been snipped in order to override the speed control.

It was like that when I got it, but after some research it seemed that it shouldn't be an issue, however, it appears it is so this weekend. I guess step one is getting in the dash and reconnecting those wires.

 

[TwistedCon]

Well I am officially stumped and being on vacation away from the car isn't helping ease my mind so hoping I can get some ideas from you all upon my return.

Loving my LX and its quirks except for the terrible ride. So while I was in Japan I remembered about Impex and ordered some new globes (was getting 3 marks on the graduation test). Got them installed and bled the fluid. I did forget the height accumulator but I don't think that is my issue although it could be but I'll continue.

So now I have fresh fluid. 13ish marks on the test and pressures were in spec. Welp ride was exactly the same. Just down right crappy.

So I'm starting to think this error code I've had since I have gotten the car could be my problem or my steering angle sensor always reading way off in tech stream (currently have my mechanic dealing with that)

The code is C1751 which is continuous current being sent to the compressor motor. I have no lights on the dash and all the AHC functions seems to work. Up/down, sport/comfort setting (ride doesn't really get any stiffer but definitely less body roll). The one thing that doesn't work is the AHC off button. I am thinking maybe the dampening doesn't work so long as it thinks the ahc pump is running? However I have no idea what's causing this code or how to trouble shoot it sadly.

My only assumption with the steering angle sensor is that the car just doesn't know what to do because it thinks the steering wheel is turned 212 degrees or some other ridiculous number. I even checked while driving and it was still incorrect.

Open to all suggestions and appreciate the help in advance.

 

[Coin]

Well I am officially stumped and being on vacation away from the car isn't helping ease my mind so hoping I can get some ideas from you all upon my return.

Loving my LX and its quirks except for the terrible ride. So while I was in Japan I remembered about Impex and ordered some new globes (was getting 3 marks on the graduation test). Got them installed and bled the fluid. I did forget the height accumulator but I don't think that is my issue although it could be but I'll continue.

So now I have fresh fluid. 13ish marks on the test and pressures were in spec. Welp ride was exactly the same. Just down right crappy.

So I'm starting to think this error code I've had since I have gotten the car could be my problem or my steering angle sensor always reading way off in tech stream (currently have my mechanic dealing with that)

The code is C1751 which is continuous current being sent to the compressor motor. I have no lights on the dash and all the AHC functions seems to work. Up/down, sport/comfort setting (ride doesn't really get any stiffer but definitely less body roll). The one thing that doesn't work is the AHC off button. I am thinking maybe the dampening doesn't work so long as it thinks the ahc pump is running? However I have no idea what's causing this code or how to trouble shoot it sadly.

My only assumption with the steering angle sensor is that the car just doesn't know what to do because it thinks the steering wheel is turned 212 degrees or some other ridiculous number. I even checked while driving and it was still incorrect.

Open to all suggestions and appreciate the help in advance.

There is thread in here somewhere are reseting the steering angle in the LX’s with vgrs. That should help at least one issue.

 

[TwistedCon]

Sadly that didn't work. I tried resetting in techstream before I left for me trip but it wasn't changing the sensor postion just decided to add it to my mechanics to do list.