AHC | problem

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Rmarques

Joined
Jul 3, 2024
Threads
2
Messages
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Location
Portugal
I'm having a problem with the AHC and here in Portugal I don't know anyone knowledgeable enough to help me solve it, not even at the Toyota dealership. Last week we went on a one more family trip. This time for more than a week from Portugal to Sardinia | Italy.
With the car loaded with everything for more than a week, roof tent, rack, awning, 2 adults and two children, the AHC is malfunctioning.
It can't shift from N to HI and many times when I start the car it goes to LO. If you turn it off and on again, sometimes it stays in N, other times it switches to LO.
From what I could tell, it only happens, or happens more often, with the rear than with the front.

There is no loss of suspension oil.
What do you think the problem might be causing the apparent lack of suspension power? What can I do?
IMG_6449.webp

Thanks
IMG_6495.webp
IMG_6465.webp
 
You need to correct the hydraulic pressures to account for age and your added weight. Check the “ABCs of AHC” thread for a full breakdown of the procedure. It’s not difficult.
 
GTV said:
You need to correct the hydraulic pressures to account for age and your added weight. Check the “ABCs of AHC” thread for a full breakdown of the procedure. It’s not difficult.
Click to expand...
Thank you very much for your help.
Since I don't have a 100% command of English, I have some difficulty understanding everything in the ABC of AHC.
To perform these measures and adjustments, I need knowledge and tools that I don't have.

What springs do you install to compensate for the additional weight of the car? With these springs, which I think are more resistant, does the AHC continue to move up and down?

I would like to keep the AHC, but for that, the necessary interventions have to be very basic.
 
Rmarques said:
Thank you very much for your help.
Since I don't have a 100% command of English, I have some difficulty understanding everything in the ABC of AHC.
To perform these measures and adjustments, I need knowledge and tools that I don't have.

What springs do you install to compensate for the additional weight of the car? With these springs, which I think are more resistant, does the AHC continue to move up and down?

I would like to keep the AHC, but for that, the necessary interventions have to be very basic.
Click to expand...
Going off of the pictures provided.
It looks like all the weight you added is the Rooftop Tent (RTT). Other than interior cargo of course. (Family/camping stuff)

So you probably only need to turn the torsion bars up and maybe add 30mm spacers to the rear springs.

The only real way to tell is to find a way to get the systems pressures. I think the Techstream image on here has more than one language.

I don't know if this came out right. The inches (") will have to be converted to mm/cm.
1775948748643.webp
 
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x8o8drifter said:
Going off of the pictures provided.
It looks like all the weight you added is the Rooftop Tent (RTT). Other than interior cargo of course. (Family/camping stuff)

So you probably only need to turn the torsion bars up and maybe add 30mm spacers to the rear springs.

The only real way to tell is to find a way to get the systems pressures. I think the Techstream image on here has more than one language.

I don't know if this came out right. The inches (") will have to be converted to mm/cm.
View attachment 4120165
Click to expand...
Thank you very much for your help.
I'll try to get a Techstream to read the pressures and understand what the next step is.

I've read in several situations that they replaced the original springs with King springs. Is this change only useful for those with a lot of additional weight? From what I understand, the springs should only be used if you need to correct more than 0.5 MPa, correct?

If the pressure needs to be corrected to less than 0.5 MPa, should it be done with spring spacers?

Another question is: if I add spring spacers (or King springs), will it increase the rear height?

Thank you for all the help and sorry for my questions.
 
Last edited:
Hello Rmarque,
Here's the simple version of what you need to do.

Buy a Techstream cable off of Amazon or similar.
Buy an older laptop (Windows 10).
Follow the instructions on the 1st few pages of this thread to get Techstream working.

getco

FAQ Thread 'How-To: TechStream In 5 Minutes'

Getting Techstream up and running can be a bit of a pain. Hopefully this helps someone get started quickly.

Step 1: Purchase an OBD-II / Mini-VCI interface.
- I have sold out of my cables and supply chains are back in order, so no reason to purchase more. Anything like this will work: Mini-VCI cable on eBay

Step 2: Download Hypervisor
  • Like
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After you've gotten Techstream up and running, do the following checks...

AHC Height Check

Check Height at Normal Height at All 4 Corners (Level Ground, SUV Running):
- Front should be 19.75” Hub Center to Fender
- Rear should be 20.5” Hub Center to Fender

Adjust Torsion Bars to get the Front Cross Level
1 Complete (360 Degree) Turn on 1 Torsion Bar Bolt will raise / lower that corner ~1/8”

The goal is less than 1/4” Difference

After the Front is Cross Level...

AHC Pressure Test

SUV with a Full Tank of Gas.
SUV on Level Ground.
Disconnect Fluid Temperature Sensor (Optional…)
- On the side of the pump assembly, rear connector with 2 wires
- Center connector with 3 wires is the pressure sensor
- Forward connector with 2 heavier blue and white wires is for the pump motor

Connect the TechStream Cable to the OBDII Port under the dash.
Start Oracle VM VirtualBox.
Start TechStream.
Enter Vehicle Information.
Double Click on AHC.
Click on Data List.

***Change Vehicle Height to L.
Wait 60 Seconds.
Change Vehicle Height from L to N.
Wait 30 Seconds after N is reached.
Read Front Pressure.
Front Pressure should be 6.9 MPa.

If Front Pressure is Higher than 6.9 MPa, adjust Torsion Bars.
1 Complete (360 Degree) Turn of Both Torsion Bar Bolts will lower the Pressure by 0.2 MPa

After Adjusting Torsion Bars, Repeat Step ***.
If Front Pressure is now 6.9 MPa, the Front is Correct.

Read Rear Pressure.
Rear Pressure should be between 5.6 & 6.7 MPa

If Rear is not in Spec, purchase new rear AHC springs (i.e. 48231-6A780 / Brown) or 30mm spacers.

You only need to Install Higher Rate Rear Coil Springs (like King Springs...) if you're always carrying extra weight (like an Aftermarket Steel Rear Bumper).

Installing New Rear Coil Springs and / or Spring Spacers will not change the Rear Height of your SUV.
It will only change the Pressure in the Rear of the AHC system.

The AHC System supports part of the weight of your SUV (via Hydraulic Pressure), while the Front Torsion Bars and Rear Coil Springs support the rest of the weight of your SUV.
The more weight the Torsion Bars and Coil Springs support, the less weight the AHC has to support.
There is a happy medium as to how much weight each supports.

Note: You should also replace your AHC Fluid (if it hasn't been done recently), perform a Graduation Test (to make sure your Globes are healthy), and perform a Pump Test (to make sure your Pump is healthy).

I hope this helps.
Tom
 
Last edited:
Snow Wagon said:
Hello Rmarque,
Here's the simple version of what you need to do.

Buy a Techstream cable off of Amazon or similar.
Buy an older laptop (Windows 10).
Follow the instructions on the 1st few pages of this thread to get Techstream working.

getco

FAQ Thread 'How-To: TechStream In 5 Minutes'

Getting Techstream up and running can be a bit of a pain. Hopefully this helps someone get started quickly.

Step 1: Purchase an OBD-II / Mini-VCI interface.
- I have sold out of my cables and supply chains are back in order, so no reason to purchase more. Anything like this will work: Mini-VCI cable on eBay

Step 2: Download Hypervisor
  • Like
  • Love

After you've gotten Techstream up and running, do the following checks...

AHC Height Check

Check Height at Normal Height at All 4 Corners (Level Ground, SUV Running):
- Front should be 19.75” Hub Center to Fender
- Rear should be 20.5” Hub Center to Fender

Adjust Torsion Bars to get the Front Cross Level
1 Complete (360 Degree) Turn on 1 Torsion Bar Bolt will raise / lower that corner ~1/8”

The goal is less than 1/4” Difference

After the Front is Cross Level...

AHC Pressure Test

SUV with a Full Tank of Gas.
SUV on Level Ground.
Disconnect Fluid Temperature Sensor (Optional…)
- On the side of the pump assembly, rear connector with 2 wires
- Center connector with 3 wires is the pressure sensor
- Forward connector with 2 heavier blue and white wires is for the pump motor

Connect the TechStream Cable to the OBDII Port under the dash.
Start Oracle VM VirtualBox.
Start TechStream.
Enter Vehicle Information.
Double Click on AHC.
Click on Data List.

***Change Vehicle Height to L.
Wait 60 Seconds.
Change Vehicle Height from L to N.
Wait 30 Seconds after N is reached.
Read Front Pressure.
Front Pressure should be 6.9 MPa.

If Front Pressure is Higher than 6.9 MPa, adjust Torsion Bars.
1 Complete (360 Degree) Turn of Both Torsion Bar Bolts will lower the Pressure by 0.2 MPa

After Adjusting Torsion Bars, Repeat Step ***.
If Front Pressure is now 6.9 MPa, the Front is Correct.

Read Rear Pressure.
Rear Pressure should be between 5.6 & 6.7 MPa

If Rear is not in Spec, purchase new rear AHC springs (i.e. 48231-6A780 / Brown) or 30mm spacers.

You only need to Install Higher Rate Rear Coil Springs (like King Springs...) if you're always carrying extra weight (like an Aftermarket Steel Rear Bumper).

Installing New Rear Coil Springs and / or Spring Spacers will not change the Rear Height of your SUV.
It will only change the Pressure in the Rear of the AHC system.

The AHC System supports part of the weight of your SUV (via Hydraulic Pressure), while the Front Torsion Bars and Rear Coil Springs support the rest of the weight of your SUV.
The more weight the Torsion Bars and Coil Springs support, the less weight the AHC has to support.
There is a happy medium as to how much weight each supports.

Note: You should also replace your AHC Fluid (if it hasn't been done recently), perform a Graduation Test (to make sure your Globes are healthy), and perform a Pump Test (to make sure your Pump is healthy).

I hope this helps.
Tom
Click to expand...
Fantastic explanation. Thank you so much for all the help.
I also found this in my searches, what do you think? Springs
 
Hello Rmarques,
The Springs you linked above are for a 200 Series Land Cruiser, not a 100 Series (1998 to 2007).
Is your LC Right Hand Drive or Left Hand Drive?
For RHD LCs, the Rear Coil Springs are the Same Size (Driver on the Right, Fuel Tank on the Left).
For LHD LCs, the Rear Coil Springs are Different Sizes (Driver and Fuel Tank on the Left, so the Left Spring is Longer to Compensate).

If RHD, I'd recommend Toyota Part Number 48231-6A780 for Both Rear Coil Springs.

If LHD, I'd recommend:
- 48231-6A770 Right
- 48231-6A780 Left (Heavier / Longer due to Gas Tank and Driver)

Enjoy.
Tom
 
Snow Wagon said:
Hello Rmarques,
The Springs you linked above are for a 200 Series Land Cruiser, not a 100 Series (1998 to 2007).
Is your LC Right Hand Drive or Left Hand Drive?
For RHD LCs, the Rear Coil Springs are the Same Size (Driver on the Right, Fuel Tank on the Left).
For LHD LCs, the Rear Coil Springs are Different Sizes (Driver and Fuel Tank on the Left, so the Left Spring is Longer to Compensate).

If RHD, I'd recommend Toyota Part Number 48231-6A780 for Both Rear Coil Springs.

If LHD, I'd recommend:
- 48231-6A770 Right
- 48231-6A780 Left (Heavier / Longer due to Gas Tank and Driver)

Enjoy.
Tom
Click to expand...
I didn't understand why you say the springs in the link are for the VDJ200.
 
I searched the entire IH8MUD forum for TTCS-2168.
There are No Results in the 100 Series Section.
There are Multiple Results in the 200 Series Section.
Therefore, it appears people are using them on 200 Series, not 100 Series.

You need AHC Specific Rear Coil Springs.
You're welcome to use whatever you want.

Enjoy.
Tom
 
From your description, it leads me to think that your 100 series body weight is too heavy for your AHC. You need to upgrade the carrying capacity of your suspension, stiffen up the coil springs (higher spring rate) in the back and beefier torsion bars in the front.
 
Snow Wagon said:
I searched the entire IH8MUD forum for TTCS-2168.
There are No Results in the 100 Series Section.
There are Multiple Results in the 200 Series Section.
Therefore, it appears people are using them on 200 Series, not 100 Series.

You need AHC Specific Rear Coil Springs.
You're welcome to use whatever you want.

Enjoy.
Tom
Click to expand...
Hi Tom,
Thank you for your comment, which I appreciate.

I just asked because the link says it's only for the LC100 with AHC.

I just want to gather as much information as possible and learn, that's why I asked.

In the past I've had problems because of mechanics who don't know what they're doing and end up causing more damage than they fix. In the case of the LC100 with AHC here in Portugal, there are very few, and even the Toyota dealerships themselves don't have the knowledge to repair it. That's why I'm trying to learn as much as possible about the subject.

I'd like to ask another question: do the original springs for AHC come in more than one tension rating?
Are the part numbers you're indicating the same as the originals, or possibly with a higher tension rating?

Thanks for your help.
 
OEMGUY0720 said:
From your description, it leads me to think that your 100 series body weight is too heavy for your AHC. You need to upgrade the carrying capacity of your suspension, stiffen up the coil springs (higher spring rate) in the back and beefier torsion bars in the front.
Click to expand...
Thank you for the information.

I'm still trying to learn as much as possible about the system.
Thanks
 
Hello Rmarques,
Please answer my question above about RHD or LHD.

As far as I know, the Rear Coil Spring Toyota part numbers I gave you above are the stiffest / highest spring rate Toyota made specifically for AHC.
There have been other part numbers for Toyota rear springs posted to this forum, but I don't believe they've ever been verified to be AHC specific.
The only other option that I know of for Rear Coil Springs specifically designed for AHC is the King Springs (KTRS-79), but they are designed for a vehicle that has additional weight all the time.
If you install King Springs on a stock weight vehicle that's typically driven around with just the driver, no passengers, no additional weight, you may not like the bouncy ride.

The absolute 1st thing you need to do is follow my 1st post and get Techstream working and find out what your AHC pressures are.
I'm guessing your current rear coil springs are old / ineffective, making your rear pressure too high at stock weight.
Once you add passengers, tools, camping gear, etc., the AHC system can't keep up.
I'm also guessing that your torsion bars will need adjusted to fix your front pressures.

Without Techstream, we have no idea what your pressures are.
Get Techstream working, go through my procedure above, then post your pressure values to this thread.

Good luck.
Tom
 
Also, cranking up the front torsions to fix the front pressures might actually fix the rears too.

I'd do these in this order.

Get a Techstream setup. (Old cheap Win 10 laptop and that Mini-VCI Cable) Do not use the disc that comes with the cable, its full of viruses/malware)
Download/install the Virtual Box image on here that has Techstream on it already.
Follow the ABCs of AHC and get the pressures. Screen Cap them or take a pic and post them.

Do that 1st then we can narrow it down more.
 
Few orher comments:
1. Priority is to read the pressures. As an alternative to techstream you have some dedicated totota scanners that will read the AHC data. Simpler to user (I couldn’t get techstream to work)
2. It is likely you will need to tigthen the front torsion bars. If they are already tigthened to the max you will need to re-index them meaning releasing them to start from a ‘tighter point’ and then tigthening from there on
3. For the back and the front you adjust the AHC ride height sensors (2 in front, 1 in back) to get to a correct pressure
4. As a quick cheap stopgap to renewing the back springs, you could just add a spacer which will have the same effect.

I would advise to replace the AHC once every 3-4 years for optimal performance.
If the spheres are shot (read pogo stick section in ABC of AHC) they need replacement. Best place to source parts is amayama which ships to europe and is competitive price wise. Their website gives you all the part numbers by model type so you van’t go wrong ordering. The change of AHC sphere is straightforward as described in the post.

You are right to preserve AHC it is a great system.

If the AHC is causing immediate problems, I would tighten in the field the two front torsion bars by 2 turns. That should relieve AHC until you can do it properly.
 
First, I want to thank you for your responses and suggestions; you have been fantastic.
Let's see if I can answer you all without forgetting anything and give a little more context to the situation.

-The car is LHD

-The car without the roof tent (I removed it again today) and without our personal items, but keeping the roof rack, awning, drawers in the trunk, rescue equipment, and other things I always carry, the AHC works perfectly (it's like that at the moment).

-The car is level in all corners.
-Two years ago, at the local official Toyota dealership, a lift was done by adjusting the sensors (+-2cm), and the torsion bars were also tightened. I think all of this was done by eye without any pressure readings from the system.

-About 20,000km, all the suspension oil was changed.
-On that last trip, when the car was fully loaded, this failure occurred. It seemed to me that the front still lifted, but the rear couldn't. Now that I've removed some of the car's weight, it's working perfectly again and is at the ideal height for me.

Another issue is that I'm in Portugal, but I bought the car in the Netherlands, and due to the salt in winter, it had some corrosion (very little), and I've been replacing some components because they had a little rust. One of the things on the replacement list is the springs, because in addition to a little rust, they have 290,000 km on them.
Therefore, I will replace the springs at the next opportunity.

Following your advice, I will try to measure the system pressures.

Once again, I am very grateful for all the help. Here in Portugal, I don't know anyone with AHC; everyone I know who had it has had it removed.
 
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