AHC 81k miles - squatting (6 Viewers)

[Piney1]

Question on the AHC: My 2005 LX just turned 81k miles, it had 71k on it in November of 24 when I became the second owner. It is stock other than the LC200 wheels and better rubber. The AHC has been working as designed until two weeks ago. Lowered it to let my mother-in-law get in (she is feeble and 86). When I drove after that, it was bouncy. Once I stopped and restarted, it seemed to get better. I’ve loved smooth ride on this thing. Then, I noticed that the rear was squatting about an inch lower than normal.

Techstream showed no codes or errors. The screenshot below on the right is after I raised it so it is communicating just fine. Changing from firm to sport makes it get rough and that is not normal. Pic on left is before the squat, on right is now.

Is it worth fixing this? I’d love to get it done and keep it stock.
Is there an aftermarket solution that retains the ability to control ride and height from inside the vehicle?
I’m not far from Johnson City, TN - would love to know if anyone knows a good tech for this. The local dealer is OK but I’d prefer a specialist that ain’t a dealer.

 

[excessive]

its probably the age, not the miles

 

[jaewastooshort]

just from memory (can't remember operating specs), the front and rear pressures look really high. torsion bars are an easy adjustment, but you may need new springs in the rear to get in spec if it's way out. do your height sensors all look ok?

 

[Piney1]

just from memory (can't remember operating specs), the front and rear pressures look really high. torsion bars are an easy adjustment, but you may need new springs in the rear to get in spec if it's way out. do your height sensors all look ok?

Visually, yes - they look good to my untrained eye.

Should have added, fluid level is good in the reservoir.

When I put it in high, it seems to take longer than normal for the light to stop flashing but it does raise fully. No signs of any leakage.

 

[jaewastooshort]

If you haven't yet, go through this comprehensive guide: The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/

I looked up the specs there, and yeah, your front and rear pressures are both high.

Measure your front/rear pressures, accumulator pressure, and sensor heights using Techstreamand a Mini-VCI cable, a manual inline gauge, or an advanced OBDII reader (iCarsoft, TYT II, OBDLink, VGate, etc.)

• Front spec: 6.9MPa +/- 0.5
• Rear spec: 5.6-6.7MPa
• Accumulator spec: 10-10.6MPa

 

[dchilds]

Have you looked at the height sensors themselves?

 

[Jack90210]

The AHC system is having to compensate for the loss of spring capacity that happens over time, and the harshness that you feel in "Sport" is likely related (though there may be other causes, like fatigued globes, as well).

It's likely that you can mitigate these symptoms with a few turns of the torsion bar adjuster and by removing the 3rd-row seats in the rear (if they are still there, looks like it in the first pic).

 

[Piney1]

The AHC system is having to compensate for the loss of spring capacity that happens over time, and the harshness that you feel in "Sport" is likely related (though there may be other causes, like fatigued globes, as well).

It's likely that you can mitigate these symptoms with a few turns of the torsion bar adjuster and by removing the 3rd-row seats in the rear (if they are still there, looks like it in the first pic).

I have the third row seats in the garage now. We take the GX if there is a need to haul more than 5.

I’ll try that adjustment of the torsion bar. I’ll search the threads for how to do this if it ain’t readily apparent.

Thanks.

 

[jaewastooshort]

I have the third row seats in the garage now. We take the GX if there is a need to haul more than 5.

I’ll try that adjustment of the torsion bar. I’ll search the threads for how to do this if it ain’t readily apparent.

Thanks.

It's pretty simple. Follow the torsion bar from the front control arm to the rear bracket, and in the bracket there is a large bolt that runs through, "B" in this pic:

(source: For those with torsion bar questions - https://forum.ih8mud.com/threads/for-those-with-torsion-bar-questions.491948/ )

The thread has a good guide to adjustment. Between this thread on adjusting the torsion bar, and the previous one I linked on AHC setup, you should easily be able to get the front pressure back in-spec, and I'd be willing to bet that it will solve your harsh ride issue and allow the system to put more effort into keeping the rear height set appropriately. If you don't want to bother with replacing the rear springs, a 30mm spacer might be enough to get you back to the correct height and bring your rear pressure back to where it should be.

 

[Piney1]

It's pretty simple. Follow the torsion bar from the front control arm to the rear bracket, and in the bracket there is a large bolt that runs through, "B" in this pic:
View attachment 3953976
(source: For those with torsion bar questions - https://forum.ih8mud.com/threads/for-those-with-torsion-bar-questions.491948/ )

The thread has a good guide to adjustment. Between this thread on adjusting the torsion bar, and the previous one I linked on AHC setup, you should easily be able to get the front pressure back in-spec, and I'd be willing to bet that it will solve your harsh ride issue and allow the system to put more effort into keeping the rear height set appropriately. If you don't want to bother with replacing the rear springs, a 30mm spacer might be enough to get you back to the correct height and bring your rear pressure back to where it should be.

Thanks for the links and information. I’ll have to get this done this weekend. I use an iPad almost exclusively and the font is yellow on the headings of those pages - nearly invisible to my 57 year old eyes.

To summarize though - do it a level surface, do not jack it up, keep suspension in middle setting and then adjust each of the torsion bars the same amount? The droopy drawers look is killing me.

 

[jaewastooshort]

Generally, if you're just doing a tune-up, yes.

In a properly functioning system, the height is measured by the height sensors at each wheel, and the AHC system adjusts pressure in the hydraulic struts in order to keep the ride height set.

Since your pressures are way higher than the specified range for normal height/operation, that indicates that your springs are not doing enough work and the AHC system is increasing pressure to compensate.

Adding additional preload to the torsion bars will force them to take more of the weight, which will bring the front pressures down. If you have any difference in height measurement from side to side on the front, you would adjust the torsion bar preload on the lower side to bring it back to level left-to-right, then adjust the preload on both torsion bars equally to decrease the AHC pressure.

Once you have your front pressure in-spec (needs to come down about 3.5 MPa based on the screenshot you posted), the system may have enough capacity to compensate in the rear. However, it also seems possible that your rear height sensor needs to be adjusted or repaired, since it's sagging so much in the rear. If we assume that the sensor is ok and it's just a pressure issue, you may need to replace your rear springs (or add a 30mm spacer) to reduce the load the hydraulic system is being forced to carry. If the height sensor is off in the back for some reason, you could put a much stronger spring in the back and the system would just reduce pressure in the rear shocks to try and keep the height at what it sees as "normal", which could keep it where it is currently.

A lot of small things to check.

 

[IndroCruise]

Question on the AHC: My 2005 LX just turned 81k miles, it had 71k on it in November of 24 when I became the second owner. It is stock other than the LC200 wheels and better rubber. The AHC has been working as designed until two weeks ago. Lowered it to let my mother-in-law get in (she is feeble and 86). When I drove after that, it was bouncy. Once I stopped and restarted, it seemed to get better. I’ve loved smooth ride on this thing. Then, I noticed that the rear was squatting about an inch lower than normal.

Techstream showed no codes or errors. The screenshot below on the right is after I raised it so it is communicating just fine. Changing from firm to sport makes it get rough and that is not normal. Pic on left is before the squat, on right is now.

Is it worth fixing this? I’d love to get it done and keep it stock.
Is there an aftermarket solution that retains the ability to control ride and height from inside the vehicle?
I’m not far from Johnson City, TN - would love to know if anyone knows a good tech for this. The local dealer is OK but I’d prefer a specialist that ain’t a dealer.
View attachment 3953731

AHC Pressures:

IF these are the AHC pressure readings AFTER changing from “LO” height to “N” height and AFTER waiting for ~30 seconds to ensure that the raise has completed and the AHC Pump has stopped:

• Front AHC spec: 6.9MPa +/- 0.5 versus Front Actual 10.7 Mpa
• Rear AHC spec: 5.6-6.7MPa versus Rear Actual 7.9 Mpa
• Accumulator spec: 10-10.6MPa versus Actual 10.7 Mpa

THEN

• At these very high Front and Rear over-pressures in the AHC system, damping will be poor, ride quality will be poor and will feel very ‘springy’ and rough -- caused by any or all of:
• steady degradation with age and use of the load-carrying ability of springs/torsion bars, resulting in excessive load carried by the AHC system as already described above by others, and/or,
• the actual vehicle ‘ride height’ as measured at hub-to-fender on each wheel at N height setting is too high (should be around 19.75 inches Front and 20.50 inches Rear -- more height means less load carried by springs/torsion bars and more load carried by AHC system = higher pressures), and/or,
• vehicle weight (of everything in or on the vehicle including fittings, accessories, fluids, people) exceeds the guidelines found in the Factory Service Manual (FSM) and the Owners Manual for loads above the ex-factory kerb weight of the vehicle = higher AHC pressures,

• Note 1: The AHC pressure readings tell NOTHING about the condition of the ‘globes’,
• Note 2: Overall condition of the ‘globes’ is determined using the FSM-prescribed test at correct AHC pressures (attached),

Height Control Sensors:

Although longlasting, these are ‘wear items’ and they eventually degrade because they operate continuously in hostile underbody conditions whenever the vehicle is operating. The Height Control Sensors are simple potentiometers -- nothing ‘electronic’ inside. Their function is to provide voltage signal to the Suspension Electronic Control Unit (ECU) corresponding to the wheel height. These are among the inputs the ECU uses to actively and continuously regulate and keep constant the height of the vehicle in real time within the limits of the system -- by operating the AHC Pump and/or opening the Levelling Valves in the Control Valve Assembly as required. This is the Active Height Control (AHC) function.

For the purposes of Techstream, the Height Control Sensor voltage readings are converted to inches (or millimetres). At “N” height setting all three Height Control Sensor readings (two in Front, one at Rear) should be as a close to zero as possible (FSM-specified tolerance: +/- 0.2 inches (or +/- 5 millimetres). If there are excessive differences between these readings at “N” height, then the ECU is unable to resolve the conflicting sgnals and instead places the AHC system in “fail safe function”. In this condition, the mid-range damping setting is adopted (8 out of 16), there is no real time adaptive damping and no real time active control of ride height. The ‘ride quality’ then feels poor.

It is common for degraded Height Control Sensors to send a signal to the ECU within the FSM-specified voltage range but incorrect for the wheel height. In such cases, there will be no Diagnostic Trouble Code (DTC) recorded on Techstream (or other scanner). For this reason, absence of a Height Control Sensor DTC does not provided assurance that the Height Control Sensors are healthy. Visual inspection is insufficient. Testing of the Sensors per FSM is necessary. Replacement of old Height Control Sensors usually is prudent.

Unusual squatting at Front or Rear of a vehicle is often observed and reported in this forum without Height Control Sensor DTC’s -- and often these are resolved by replacement of aged, faulty Height Control Sensors.

In addition to the links and good explanations provided above by @jaewastooshort, see also the attached extracts from the FSM.