AHC with harsh ride (1 Viewer)

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Does flushing the fluid improve ride quality under any circumstances?
 
Not that I’ve noticed. 07 Lx470

When the car is running?
I have an 06LX, yeah only when engine is running. I noticed this 3 months ago but finally anticipated it yesterday when I picked up my daughter at school and she decided to sit at the backseat. I was at “P” parked on the shifter, she opened the backseat door, I felt the rear lower down, and 1 or 2 seconds after the backseat door was shut I felt the rear raise back up. Even the teachers on the side assisting students to the cars noticed it that’s what made me realize I still have my sanity (finally it’s not just me who felt/saw it) lol
 
Sorry for resurrecting's this old issue, but I have been doing a bunch of AHC reading and it seems many of us have this issue, and it has never been solved. I have yet to see whether a mere flush of the system fixes it. Many people on Mud and Club Lexus say things like, "It's worth a try", but no one has said, Wow, I flushed my system and it fixed the harsh ride." On one of our LXs, replacing the globes and then getting the pressure in spec didn't fix it. Is it an AHC ECU issue?

I now have a LX 570 the dealer can't sort out and I don't really feel like laying in the cold in my driveway replacing the 10 accumulators it has and flushing the system, if that won't fix the problem.

Any ideas? Thanks!

I flushed my AHC system due to a harsh ride. At the same time, I also adjusted the front torsion bars to get the front pressures back in spec. Honestly, it's difficult for me to say how much it helped. There are days where I consciously am thinking "damn, this car rides great for being 14 years old", but there are days where I get annoyed with cracks in the road. I think it helped, but didn't absolutely fix the problem. I think part of the difficulty is that once you start thinking about whether the ride is harsh or not, you start obsessing about it and can't think about anything else (maybe that's just my OCD kicking in).

I suspect that the other culprit is some of the bushings wearing. Between the AHC fluid being old and dirty, the globes being over a decade old, and all the bushings being warn down, I think it just transmits more harshness than it used to. Replace any one of those components and I think you'll see some improvement, but if you don't tackle all of them, it will never be like new again. It probably only costs $75 and take about an hour to flush the AHC fluid yourself, so it's definitely the cheapest way to start.

I've also got a squeak in my front suspension, so when I get around to it, I may replace a bunch of the bushings in the front suspension. While I'm at it, I'll probably flush the AHC fluid again (I think it's been about 5 years since I last did it) just in case. I'll try to remember and post back here if that combination seemed to do much.
 
I am determined to get to the bottom of this. I should start a crowd fund me page for financial support! :)
 
I have an 06LX, yeah only when engine is running. I noticed this 3 months ago but finally anticipated it yesterday when I picked up my daughter at school and she decided to sit at the backseat. I was at “P” parked on the shifter, she opened the backseat door, I felt the rear lower down, and 1 or 2 seconds after the backseat door was shut I felt the rear raise back up. Even the teachers on the side assisting students to the cars noticed it that’s what made me realize I still have my sanity (finally it’s not just me who felt/saw it) lol

I have 2007 LX that does the exact same except mine seems to lower in the front. I've done the ahc flush and the ride is still little harsh and bouncy.
 
I have 2007 LX that does the exact same except mine seems to lower in the front. I've done the ahc flush and the ride is still little harsh and bouncy.
Have you tried running Techstream and get the reading of both front and rear AHC pressures? How’s your tire pressure as well?
 
Have you tried running Techstream and get the reading of both front and rear AHC pressures? How’s your tire pressure as well?

I ran techstream and the neutral pressures were at 7.6, so I cranked the torsion bars and now both the front and rear neutral pressures are 6.7. I get about 7 maybe 8 graduations from low to high. I have not checked tire pressures but I'll do that tomorrow. That's a good idea.
 
Anyone ever find a fix to the roughness over small bumps? Seems counter intuitive but enough people have the same issue with ahc that there must be something common to it. I have replaced my globes and rear springs, pressures all in spec, heights all as prescribed, and only rubber bits that haven’t been changed are rear control arms and engine mounts. All if this and yet still the roughness remains. I’m about to convert to conventional.
 
P rated tires at stock tire pressure made a noticable difference. E rated tires at E pressures make the ride harsh to me.

I need to refresh some of my bushings at, some are now at 215k. It's somewhere on my list of todos. Maybe this summer. I expect that will smooth things out.
 
Anyone ever find a fix to the roughness over small bumps? Seems counter intuitive but enough people have the same issue with ahc that there must be something common to it. I have replaced my globes and rear springs, pressures all in spec, heights all as prescribed, and only rubber bits that haven’t been changed are rear control arms and engine mounts. All if this and yet still the roughness remains. I’m about to convert to conventional.
FWIW, my 99 w/o AHC had similar/worse harshness over small bumps to my 06 with AHC now. It was less noticeable in the 99 because it was more harsh on everything. With AHC, you get buttery smooth ride quality at higher speeds so I think the similar harshness levels at lower speeds stand out more. I'm still looking to soften my AHC up on the lower speeds, but I think it's worth noting that for some of us with AHC and some low-speed harshness, it's probably still softer than conventional.

What tires are you running?

*Also, how old is your fluid?
 
FWIW, my 99 w/o AHC had similar/worse harshness over small bumps to my 06 with AHC now. It was less noticeable in the 99 because it was more harsh on everything. With AHC, you get buttery smooth ride quality at higher speeds so I think the similar harshness levels at lower speeds stand out more. I'm still looking to soften my AHC up on the lower speeds, but I think it's worth noting that for some of us with AHC and some low-speed harshness, it's probably still softer than conventional.

What tires are you running?

*Also, how old is your fluid?
I’m running ko2’s at 32/35 F/R. My fluid was changed once about a year ago when I bought the truck and again a week ago when I put on new globes. Harshness for me is noticeable both at low and high speeds. In fact, the high speeds seem worse because highways around me are quite smooth and the constant moving of the headrest, rear view mirror and rest of vehicle seem more noticeable.
 
I’m running ko2’s at 32/35 F/R. My fluid was changed once about a year ago when I bought the truck and again a week ago when I put on new globes. Harshness for me is noticeable both at low and high speeds. In fact, the high speeds seem worse because highways around me are quite smooth and the constant moving of the headrest, rear view mirror and rest of vehicle seem more noticeable.
I'd start with bushings, everywhere. My 99 had a significant shift in ride quality with just new lower rear control arms. A pair of poor bushings can make a huge difference.

Have you run through the 16 step test to make sure the damping at each corner can vary?
 
I'd start with bushings, everywhere. My 99 had a significant shift in ride quality with just new lower rear control arms. A pair of poor bushings can make a huge difference.

Have you run through the 16 step test to make sure the damping at each corner can vary?
Only bushings I Have left are rear control arms which I have on order from partsouq as per your post. havent had the time to do the 16 step test yet.
 
I'd start with bushings, everywhere. My 99 had a significant shift in ride quality with just new lower rear control arms. A pair of poor bushings can make a huge difference.

Have you run through the 16 step test to make sure the damping at each corner can vary?
I noticed today that in every setting but comfort the truck seems do this pitching front to rear like the front shocks are much stiffer than the rear. This would fall in line somewhat with how the harshness seems to come from the front end. Would the 16 step test help me differentiate between a “shock” and a actuator issue?
 
I noticed today that in every setting but comfort the truck seems do this pitching front to rear like the front shocks are much stiffer than the rear. This would fall in line somewhat with how the harshness seems to come from the front end. Would the 16 step test help me differentiate between a “shock” and a actuator issue?
Not really. The shock is barely a shock without the actuator and globe. The 16-step test tells you if the corner has varying damping. That means, more or less, that it's testing if the shock/actuator/globe assembly works.

Unfortunately, it's a pretty subjective test. Fortunately, it's incredibly unlikely that all 4 corners would have failed in the same way (with the exception of all globes failed, but that would be readily obvious with the gradation test).

If you do the 16 step test and all 4 corners show varying damping and all seems more or less the same, I think that rules out many (perhaps all?) shock/globe/actuator faults.
 
Anyone ever find a fix to the roughness over small bumps? Seems counter intuitive but enough people have the same issue with ahc that there must be something common to it. I have replaced my globes and rear springs, pressures all in spec, heights all as prescribed, and only rubber bits that haven’t been changed are rear control arms and engine mounts. All if this and yet still the roughness remains. I’m about to convert to conventional.

In addition to the comments by @suprarxnut7 and others and as a rough-and-ready indicative-only kind of test, you could watch “Front Wheel Step” and “Rear Wheel Step” in real time on Techstream (with someone else driving) and see whether the “step changes” seem to correspond to road conditions.

Why only “Front” and “Rear”? Because the LC100/LX470 AHC/TEMS system is a two-channel, front-rear system, not a four-channel system.

Watching on Techstream shows the instructions being given by the ECU to the Damping Force Control Actuators (to which the ‘globes’ are attached and to which the ‘Shock Absorbers’ are connected). The “step changes” within the Actuator run from Step 1 (softest) to Step 16 (hardest). The range of steps used is determined to some extent by the position of the control switch on the console – from Comfort through to Sport2 – and you can experiment with this. When the vehicle is at rest, or if there is a fault which causes the ECU to put the system into ‘fail safe mode’, then Step 8 is adopted by the ECU and transmitted to the Actuators.

As @suprarxnut7 already mentioned, the AHC Shock Absorber is a simple hydraulic strut with no gas inside. “Damping” is all about controlling the speed of suspension movements – up and down – and in the AHC suspension, this is done mainly by restricting the flow of fluid through the Actuators to and from the Shock Absorbers and the ‘globes’. The ‘globes’ act like gas springs. The Actuators control and vary the rate of fluid flow – more fluid flowing more quickly through the Actuator gives a softer ride and a harder, flatter ride occurs when less fluid flows through the Actuator more slowly. (As an aside: This is also why, when AHC pressures are out of their specified range, high or low, damping is poor and the ride is harsh -- and also why the ride is poor when the 'globes' have lost nitrogen pressure -- worn-out -- and the 'gas springs' are weak).

Unlike a conventional suspension, in an AHC vehicle this flow restriction (or “damping” of the up-and-down suspension speeds) is variable continuously in real time. The ECU adapts damping automatically to road conditions using inputs from the Height Control Sensors, Wheel Speed Sensors, the ABS Braking System, etc, etc – and then varies the tiny “step motors” within the Actuators in up to 16 Steps. This changes the flow rate of fluid through the Actuator. The “Steps” continuously vary – provided the system is healthy and not in ‘fail safe mode’. Vehicle squat and dive (front and rear) are controlled in a similar way.

Initially called Toyota Electronic Modulated Suspension (TEMS), more modern versions are called Adaptive Vehicle Suspension (AVS).

Conflicts between the ECU and the Damping Force Control Actuators should show as a DTC.

A common occurrence of a ‘fail safe mode’ arises when there is a fault or widely differing signals being sent to the ECU by the Height Control Sensors. The ECU then selects ‘fail safe mode’ and locks the Damping Force Control Actuators at Step 8. A seemingly harsh ride is experienced and often seems more prominent at low speeds around town over minor bumps. High tyre pressures or stiff-walled “E” rated tyres accentuate this effect. (Toyota/Lexus nominate “P” rated tyres at around 32 psi on LC100/LX470 in most parts of the world).

As LC100/LX470 vehicles get older, problems caused by Height Control Sensors and their connectors and harnesses become more common.

Height Control Sensor faults may or may not show as DTC – perhaps because they are simple potentiometer devices sending voltage signals and may need a complete absence of signal -- not just an incorrect signal -- to show as a DTC. It is for this reason that real time on-road observation on Techstream of the Front Wheel Step and Rear Wheel Step may be helpful.

Given the symptoms you describe, and unless all your Height Control Sensor readings on Techstream are close to zero, then it would be unsurprising if your vehicle is in ‘fail safe mode’ and that the Height Control Sensors need attention.

If all is well with the Height Control Sensors and they prove to be healthy by internal inspection and electrical testing per FSM, then it is time to consider issues with harnesses affecting connectivity, problems with Damping Force Control Actuators themselves, and ultimately issues with the ECU itself. ECU problems are very rare, Actuators problems occur but are not common.

Some real time observations can give an indication of what is happening with the Damping Force Control Actuators – indicative because it only tells what instructions the ECU is sending, does not tell directly what the Damping Force Control Actuators actually are doing …..

Observe “Damping Force Switch 1” (TSW1 in FSM) and “Damping Force Switch 2” (TSW2 in FSM) on Techstream in real time while the vehicle is in motion also is a helpful indicator of what instructions the TEMS part of the ECU is sending to the Damping Force Control Actuators. Different combinations of the settings of these switches will be noticed depending on the position of console switch when moved through the four positions from “Comfort” through to “Sport2”.

If you have the time and inclination to continue real time tests with Techstream, you also can monitor “SLFG” (front Solenoid Gate Valve ) and “SLRG” (rear Solenoid Gate Valve) in the Control Valve Assembly as they are the two solenoids, also within the Control Valve Assembly, that normally and hydraulically connect the left and right shock actuators. If one or both are ON when driving straight then your left/right sides are isolated which will definitely stiffen the ride -- and that is not supposed to happen. The Gate Valves are suppose to isolate only when cornering with a bit of speed and steering wheel angle, when enhanced roll stability and stiffness is desired.

Lastly, you may find some common ground in the following link to Post #20 by @cruiser03 in the thread below and his conclusion further on in Post #22 in the same thread.

AHC does large accumulator affect damping? - https://forum.ih8mud.com/threads/ahc-does-large-accumulator-affect-damping.793110/#post-9045821

The thread also contains insightful inputs and test methods along the way from @PADDO and @uHu.

In this case, @cruiser03 is using the “Damping Force Controlling Condition Check” on Pages 5 and 6 of the attachment to discern differences in Damping Force Control Actuator performance on each corner.

Hopefully your situation is resolved much more easily!!
 

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In addition to the comments by @suprarxnut7 and others and as a rough-and-ready indicative-only kind of test, you could watch “Front Wheel Step” and “Rear Wheel Step” in real time on Techstream (with someone else driving) and see whether the “step changes” seem to correspond to road conditions.

Why only “Front” and “Rear”? Because the LC100/LX470 AHC/TEMS system is a two-channel, front-rear system, not a four-channel system.

Watching on Techstream shows the instructions being given by the ECU to the Damping Force Control Actuators (to which the ‘globes’ are attached and to which the ‘Shock Absorbers’ are connected). The “step changes” within the Actuator run from Step 1 (softest) to Step 16 (hardest). The range of steps used is determined to some extent by the position of the control switch on the console – from Comfort through to Sport2 – and you can experiment with this. When the vehicle is at rest, or if there is a fault which causes the ECU to put the system into ‘fail safe mode’, then Step 8 is adopted by the ECU and transmitted to the Actuators.

As @suprarxnut7 already mentioned, the AHC Shock Absorber is a simple hydraulic strut with no gas inside. “Damping” is all about controlling the speed of suspension movements – up and down – and in the AHC suspension, this is done mainly by restricting the flow of fluid through the Actuators to and from the Shock Absorbers and the ‘globes’. The ‘globes’ act like gas springs. The Actuators control and vary the rate of fluid flow – more fluid flowing more quickly through the Actuator gives a softer ride and a harder, flatter ride occurs when less fluid flows through the Actuator more slowly. (As an aside: This is also why, when AHC pressures are out of their specified range, high or low, damping is poor and the ride is harsh -- and also why the ride is poor when the 'globes' have lost nitrogen pressure -- worn-out -- and the 'gas springs' are weak).

Unlike a conventional suspension, in an AHC vehicle this flow restriction (or “damping” of the up-and-down suspension speeds) is variable continuously in real time. The ECU adapts damping automatically to road conditions using inputs from the Height Control Sensors, Wheel Speed Sensors, the ABS Braking System, etc, etc – and then varies the tiny “step motors” within the Actuators in up to 16 Steps. This changes the flow rate of fluid through the Actuator. The “Steps” continuously vary – provided the system is healthy and not in ‘fail safe mode’. Vehicle squat and dive (front and rear) are controlled in a similar way.

Initially called Toyota Electronic Modulated Suspension (TEMS), more modern versions are called Adaptive Vehicle Suspension (AVS).

Conflicts between the ECU and the Damping Force Control Actuators should show as a DTC.

A common occurrence of a ‘fail safe mode’ arises when there is a fault or widely differing signals being sent to the ECU by the Height Control Sensors. The ECU then selects ‘fail safe mode’ and locks the Damping Force Control Actuators at Step 8. A seemingly harsh ride is experienced and often seems more prominent at low speeds around town over minor bumps. High tyre pressures or stiff-walled “E” rated tyres accentuate this effect. (Toyota/Lexus nominate “P” rated tyres at around 32 psi on LC100/LX470 in most parts of the world).

As LC100/LX470 vehicles get older, problems caused by Height Control Sensors and their connectors and harnesses become more common.

Height Control Sensor faults may or may not show as DTC – perhaps because they are simple potentiometer devices sending voltage signals and may need a complete absence of signal -- not just an incorrect signal -- to show as a DTC. It is for this reason that real time on-road observation on Techstream of the Front Wheel Step and Rear Wheel Step may be helpful.

Given the symptoms you describe, and unless all your Height Control Sensor readings on Techstream are close to zero, then it would be unsurprising if your vehicle is in ‘fail safe mode’ and that the Height Control Sensors need attention.

If all is well with the Height Control Sensors and they prove to be healthy by internal inspection and electrical testing per FSM, then it is time to consider issues with harnesses affecting connectivity, problems with Damping Force Control Actuators themselves, and ultimately issues with the ECU itself. ECU problems are very rare, Actuators problems occur but are not common.

Some real time observations can give an indication of what is happening with the Damping Force Control Actuators – indicative because it only tells what instructions the ECU is sending, does not tell directly what the Damping Force Control Actuators actually are doing …..

Observe “Damping Force Switch 1” (TSW1 in FSM) and “Damping Force Switch 2” (TSW2 in FSM) on Techstream in real time while the vehicle is in motion also is a helpful indicator of what instructions the TEMS part of the ECU is sending to the Damping Force Control Actuators. Different combinations of the settings of these switches will be noticed depending on the position of console switch when moved through the four positions from “Comfort” through to “Sport2”.

If you have the time and inclination to continue real time tests with Techstream, you also can monitor “SLFG” (front Solenoid Gate Valve ) and “SLRG” (rear Solenoid Gate Valve) in the Control Valve Assembly as they are the two solenoids, also within the Control Valve Assembly, that normally and hydraulically connect the left and right shock actuators. If one or both are ON when driving straight then your left/right sides are isolated which will definitely stiffen the ride -- and that is not supposed to happen. The Gate Valves are suppose to isolate only when cornering with a bit of speed and steering wheel angle, when enhanced roll stability and stiffness is desired.

Lastly, you may find some common ground in the following link to Post #20 by @cruiser03 in the thread below and his conclusion further on in Post #22 in the same thread.

AHC does large accumulator affect damping? - https://forum.ih8mud.com/threads/ahc-does-large-accumulator-affect-damping.793110/#post-9045821

The thread also contains insightful inputs and test methods along the way from @PADDO and @uHu.

In this case, @cruiser03 is using the “Damping Force Controlling Condition Check” on Pages 5 and 6 of the attachment to discern differences in Damping Force Control Actuator performance on each corner.

Hopefully your situation is resolved much more easily!!
Indro, this is awesome information, really appreciate you taking the time to do this.

This morning I took a ride while checking in this parameters you recommended.

First, the damping force switch definitely changed values as I switched through the comfort/sport settings. Additionally, i can subjectively say that the dampers are reacting as it goes from minor discomfort in comfort mode to pretty sharp bumps felt and minor Bucking front to back in sport mode.

Next, the front and rear wheel step are definitely changing while driving and not stuck in what would be a fail safe mode (I’m assuming these would be stuck at a single digit if it was in fail safe). Also, they range from approximately 1-6 in comfort mode to 8-12 in sport II mode. My sensors while parked are all within +/- 6mm of 0 although I will admit that they were adjusted to get the appropriate hub to fender height, not necessarily to get as close to 0 as possible.

I also checked SLFG/SLRG and They are at least being told to stay closed while driving straight and open when cornering sharply.

My next step will be to do the 16 step damper check which I think I have a fairly straight handle on now. I basically connect the two prescribed fuses with something like alligator clips and move the dampers through all their settings while subjectively checking the rebound at each corner.

I will say that since I bought the truck the ride has improved somewhat due to changing out bushings, tie rods, etc but nothing I have done to the suspension has changed the underlying small bump non compliance, changing AHC fluids, getting the front pressure in spec (rear pressure is still around 7.5 despite putting in new oem springs but something tells me this isn’t the culprit of my ride problems), adjusting height sensors, and putting on all new oem globes.

thanks again.
 
Indro, this is awesome information, really appreciate you taking the time to do this.

This morning I took a ride while checking in this parameters you recommended.

First, the damping force switch definitely changed values as I switched through the comfort/sport settings. Additionally, i can subjectively say that the dampers are reacting as it goes from minor discomfort in comfort mode to pretty sharp bumps felt and minor Bucking front to back in sport mode.

Next, the front and rear wheel step are definitely changing while driving and not stuck in what would be a fail safe mode (I’m assuming these would be stuck at a single digit if it was in fail safe). Also, they range from approximately 1-6 in comfort mode to 8-12 in sport II mode. My sensors while parked are all within +/- 6mm of 0 although I will admit that they were adjusted to get the appropriate hub to fender height, not necessarily to get as close to 0 as possible.

I also checked SLFG/SLRG and They are at least being told to stay closed while driving straight and open when cornering sharply.

My next step will be to do the 16 step damper check which I think I have a fairly straight handle on now. I basically connect the two prescribed fuses with something like alligator clips and move the dampers through all their settings while subjectively checking the rebound at each corner.

I will say that since I bought the truck the ride has improved somewhat due to changing out bushings, tie rods, etc but nothing I have done to the suspension has changed the underlying small bump non compliance, changing AHC fluids, getting the front pressure in spec (rear pressure is still around 7.5 despite putting in new oem springs but something tells me this isn’t the culprit of my ride problems), adjusting height sensors, and putting on all new oem globes.

thanks again.
Did you ever sort this out? I've got the same issue.

New globes from Impex, new fluid, new OEM bushings alllllll around (upper and lower shock bushings, upper/lower front control arms, upper/lower rear control arms)l, panhard bushings).

Pressures are in spec - rears are actually a little low since I swapped to king springs, but prior to that they were a little high on old OEM AHC springs and it rode the same.

Doing the 16 step test on all four corners seem to indicate that the damper actuators are working properly, and it changes steps as I drive as it should.

Ride quality on little stuff SUCKS (my 700' gravel driveway is hell), but it is smooth over medium/big stuff.

I've put a lot of time, effort (rear upper shock bushings...), and money into keeping AHC, but I'm currently super dissapointed.

Any wisdom from @IndroCruise, @PADDO or @uHu ?
 
Did you ever sort this out? I've got the same issue.

New globes from Impex, new fluid, new OEM bushings alllllll around (upper and lower shock bushings, upper/lower front control arms, upper/lower rear control arms)l, panhard bushings).

Pressures are in spec - rears are actually a little low since I swapped to king springs, but prior to that they were a little high on old OEM AHC springs and it rode the same.

Doing the 16 step test on all four corners seem to indicate that the damper actuators are working properly, and it changes steps as I drive as it should.

Ride quality on little stuff SUCKS (my 700' gravel driveway is hell), but it is smooth over medium/big stuff.

I've put a lot of time, effort (rear upper shock bushings...), and money into keeping AHC, but I'm currently super dissapointed.

Any wisdom from @IndroCruise, @PADDO or @uHu ?
Sorry, no help here. I swapped to traditional suspension and still have the same issues. I swapped every rubber piece that I could see as associated with rude quality and it’s still the same. Finally gave up and really hate to sell it because the 100 series is so solid otherwise but don’t drive it more than once a week or so.
 
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