The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (6 Viewers)

[LndXrsr]

I initially put this in the Definitive list of AHC maintenance items thread, but at almost 800 posts long and growing, it's going to get buried and the thread itself is very unwieldy.

In an attempt to make as focused a summary as possible, I present "The ABCs of AHC." It's intended as a comprehensive, linear checklist for anyone who needs to get their AHC back into factory tune. Information gathered from as many sources as I could find on this forum; I take no credit for developing any of this, just bringing it all together as much as possible. Special shout outs to @PADDO, @uHu, @IndroCruise, @PabloCruise and @2001LC for many of the details, specs, and procedures I've included in here. Feedback more than welcome, will make edits as appropriate based on what I hear.


A - Assess: Figure out where you’re starting from

1. Wheels on level ground, no ramps, jacks, or stands needed for parts A, B, or C. DO NOT PUT YOURSELF PHYSICALLY UNDER THE VEHICLE FOR ANY OF THIS.
2. Get your rig loaded/unloaded to what is “typical” for your use.
   • FSM calls for no driver or passengers, full tank of fuel.
3. Measure ride height at all 4 corners from center of wheel cap vertically to fender lip on a level surface
   • Front OEM: 19.75” (50.2cm)
   • Rear OEM: 20.5” (52.1cm)
   • Drive a bit, then park in the same level place. Take 3-5 measurements and get a mean or median.
4. Measure difference in AHC tank level between H and L suspension heights
   • >7 graduations acceptable, 14 graduations new from factory
   • Need to replace globes/spheres if <7 after parts A, B, and C are complete.
   • Backlight AHC fluid tank with a light to help see fluid level
   • Again, 3-5 measurements and take a mean or median value
5. 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
   • Start car, connect Techstream, make sure you choose your exact model, not the default Land Cruiser with no AHC installed
   • Open AHC channel and select "data list" to monitor values
   • Cycle from N to L to N again. Take a screenshot of your values. There are Front R and Front L height sensors but only one rear sensor for pressure and height. May need to disconnect the AHC temp sensor to get accurate rear readings per FSM.
   • Again, 3-5 measurements and take a mean or median value for each data point.

B - Bleed: Flush out the old AHC fluid

1. Procure three 1L bottles of OEM AHC fluid (08886-81221)
2. Put AHC in Low, turn engine off
3. Suck all old fluid out of AHC tank (~1L if level was between Max/Min at N height)
4. Pour in new fluid to top of tank (~2.5L)
5. Bleed accumulator until fluid stops (long cylinder on left side frame rail) (~300mL, 10mm wrench)
   • Bleeder torque spec: 62 in-lbf (5.5 ft-lbf, 7.5 N-m)
6. Bleed one front and one rear damper (globe unit) until both front and rear are on the bump stops and fluid stops flowing (~300-400mL each)
   • Bleeder torque spec: 73 in-lbf (6.0 ft-lbf, 8.1 N-m)
   • Careful, as the car will lower significantly during this process. Don't put yourself under the vehicle!
7. Start car, put AHC in Neutral until pump stops, turn off again
8. Bleed the remaining front and rear dampers on the other side of the car for just a second until fresh fluid and no air comes out (~50mL each)
9. Start car, cycle to AHC to L then back to N
10. Top off AHC fluid in the reservoir. Should be between Max/Min at N height.
11. Recheck graduations in the tank as described in step A2. May see some improvement, may not.

C – Crank/Check: Adjust the side-to-side height and neutral pressures front/rear

1. Remeasure your ride heights as in Step A1. Measure twice, cut once.
2. Fix any left-to-right ride height imbalance, i.e. lean. This is commonly called “cross-leveling” throughout this thread. This is done entirely by adjusting the front torsion bars (TBs), not height sensors.
   • Tighten (CW) a TB nut to raise a low side, loosen (CCW) to lower a high side. 30mm wrench/socket
   • Mark your TB nuts (permanent or paint marker) so that you don’t lose track of where a full turn is
   • Place AHC in H to lessen pressure on TBs and make turning easier. Put back to N for measurements.
   • ~1/8” correction in left-to-right height imbalance per full turn of a TB nut
   • Best to turn TBs equal amounts in opposite directions until level
   • Drive a bit, repeat, measure until satisfied with left and right ride heights being equal
3. Adjust the three ride height sensors as needed to achieve as close to 0mm on all values at N in Techstream.
   • Engine off, ignition on. Monitor changes in real time on Techstream.
   • Raise: Shorten heim joint (the adjustable threaded rod) or move the top of the joint up in its slider
   • Lower: Lengthen heim joint or move the top of the joint down in its slider
   • Rear sensor only has a slider
   • <10mm (0.3-0.4in) between the two most discrepant sensors is acceptable
   • Recheck ride height as in step A2. If all sensors at/near 0mm, ride height should be very close to OEM spec, otherwise sensor(s) may be malfunctioning.
4. Adjust front N height pressures by cranking the TBs
   • Place AHC in H to lessen pressure on TBs and make turning easier
   • Lower pressures: tighten (CW) both TBs the same amount
   • Raise pressures: loosen (CCW) both TBs the same amount
   • ~0.2MPa change in pressure per full turn of a TB nut
   • Cycle H to L to N. Recheck pressures as in step A5.
5. Check rear N height pressure
   • OEM specs in step A5
   • May need to disconnect the AHC temp sensor to get accurate rear readings per FSM (Decreases pressures ~0.8-1). Try it both ways.
   • Rear pressures can be changed with new springs (OEM or King), spacers, airbags, or rear sensor height adjustments (but this last one also change the height of your rear and the car’s rake front to back).
6. Check graduations in the tank as described in step A2. Again, may see some improvement, may not.

Good luck! Hope folks find this a helpful all-in-one reference for tackling their AHC. Maybe it will prevent a few of you from ripping out a great system. Save the AHCs!

 

[LndXrsr]

Here are some of the factory documents that may help along the way. Best to check in these first if you have questions about more details from the outline in post #1.

PM me if you have anything more to add here.

 

[LndXrsr]

Some pictures for the visual learners:

Accumulator (left frame rail) with bleed screw:

Damper with bleed screw. Two on each frame rail (front/rear). Globe or sphere is the large rounded part on the right of the photo:

AHC fluid reservoir. Backlight to see fluid level better:

AHC pump underneath reservoir. Connectors can be seen in this pic. Per @PADDO, rearmost one is temp sensor to disconnect if having issues with accurate rear pressure measurements:
"It's on the side of the pump assembly, rear most connector with 2 wires, the center connector with 3 wires is your pressure and the most forward connector with the 2 heavier blue and white wires is your pump motor."

Sample Techstream photo. First 6 values are primarily what are referenced in this process:

 

[LndXrsr]

AHC 1L fluid bottles (08886-81221). They also made a 2.5L metal can (08886-01805) that was discontinued in favor of the 1L bottles, but was then reintroduced sometime in 2021 or 2022 due to 1L plastic bottles having the fluid "gel" inside them. The 1L plastic bottle issue seems primarily from mid-late 2021. Recommend checking all fluid from plastic bottles by pouring into another container and/or straining it to look for gelling prior to use.

2.5-3L works for one complete flush:

New fluid (L) vs a typical old fluid (R) during a flush:

 

[LndXrsr]

An excellent video summary and quick reference by @suprarx7nut that definitely deserves placement in this thread:

 

[LndXrsr]

AHC Mods:

Rear pressure adjustments in order of magnitude:
- Adding/removing weight over rear axle: ~1.0MPa/210lbs
- Rear sensor lift 1": +0.6MPa
- New OEM AHC springs (95 lb/in): -0-0.3MPa depending on how worn the current springs are
- 30mm spring spacers: -0.3-0.6MPa reduction
- King KTRS-79 Springs (130lb/in): -3.0MPa reduction
- OEM 100-series non-AHC or 80-series springs (170lb/in) -or- LX450 springs (150lb/in): YMMV, >3MPa reduction likely


Lifts:
- Sensor lift - adjust all three sensors to add variable static ride height, typically 0-2.5" before limiting droop travel too much. Will need to tighten front TBs to keep pressures in spec and likely need spacers or heavier springs in rear to also stay in spec.

- Japan 4x4 AHC "shock" spacers - lift the AHC hydraulic rams up by 60mm front, 40mm rear Allows AHC rams to retain their typical travel range, droop now limited by control arms again. Best for 2"+ AHC lifts.

- AHC Override Switch - pre-fab sold by Slee (now discontinued) or can be homemade using a DPDT switch. Allows for operating in L, N, or H at any speed. Downsides include increased wear on CVs, potential suboptimal operating pressures, disconnects wheel speed sensors so TEMS ride dampening adjustment is disabled.


Airbags:
- Firestone and possibly Airlift make bags that will fit an LX/LC. Best for use with towing or very intermittent heavy loads.


Please PM me if you have good summaries or assessments of other mods you've tried.

 

[AFei]

Excellent!

 

[riffman12]

Nice work! Often difficult to dig this info out of the big thread

 

[BEG]

Thanks for doing this! It might be a little early for edits, but for Section A, item 5, it might be helpful to mention alternatives to Techstream like the handheld OBD readers from iCarsoft (my recommendation is the TYT II, but there are other models) and bluetooth readers like OBDLink which can also be used to read AHC pressures without the need of a laptop.

 

[EricBikas]

@LndXrsr this is wonderful! @BEG can you elaborate on the alternatives to tech stream?

 

[katit]

Also, need some definite info on temp sensor. “May need” or “should” disconnect when pressure checking?

Also, should driver be in a car when measuring pressure? And cycling NLN?

 

[LndXrsr]

Thanks for doing this! It might be a little early for edits, but for Section A, item 5, it might be helpful to mention alternatives to Techstream like the handheld OBD readers from iCarsoft (my recommendation is the TYT II, but there are other models) and bluetooth readers like OBDLink which can also be used to read AHC pressures without the need of a laptop.

Never too early. Will toss some of that info in. My plan is at a tough crossroads between being comprehensive and succinct, but I think it's worth adding.

Also, need some definite info on temp sensor. “May need” or “should” disconnect when pressure checking?

Also, should driver be in a car when measuring pressure? And cycling NLN?

If you have definite info, that would be great to know. Everything I have read says some need to remove it, others don't. Can't pick up on a pattern as to which do or don't.

The driver should not be in the car. Will clarify in part A2.

 

[BEG]

@BEG can you elaborate on the alternatives to tech stream?

I haven't used all of them but I have experience with the iCarsoft TYT II simply because it's one of the most affordable handhelds. I tried Techstream but didn't like it. Depending on your laptop situation, it's just not packaged in a way that's comfortable to use around a vehicle. The handheld units are rugged and intuitive to use because they're designed as a car diagnostic tool. As far as AHC goes, the TYT II can read and erase AHC DTC codes, show sensor height in real time and, of course, read pressures. It's also handy for ABS, SRS and other system codes. It's also handy when bleeding brakes.

I've also seen others use OBDLink to read them. I had OBDLink but stopped using it before I knew it could read AHC information. Hopefully someone can chime in with details.

 

[riffman12]

A H C

Eeeeaassy as A B C

 

[EricBikas]

I haven't used all of them but I have experience with the iCarsoft TYT II simply because it's one of the most affordable handhelds. I tried Techstream but didn't like it. Depending on your laptop situation, it's just not packaged in a way that's comfortable to use around a vehicle. The handheld units are rugged and intuitive to use because they're designed as a car diagnostic tool. As far as AHC goes, the TYT II can read and erase AHC DTC codes, show sensor height in real time and, of course, read pressures. It's also handy for ABS, SRS and other system codes. It's also handy when bleeding brakes.

I've also seen others use OBDLink to read them. I had OBDLink but stopped using it before I knew it could read AHC information. Hopefully someone can chime in with details.

After reading your first post I did a little reading and just ordered the OBDLink MX+ (iOS user). I want it ONLY for reading my ACH pressures and keeping it calibrated. Thank you for the information!

 

[trdcorolla]

Never too early. Will toss some of that info in. My plan is at a tough crossroads between being comprehensive and succinct, but I think it's worth adding.



If you have definite info, that would be great to know. Everything I have read says some need to remove it, others don't. Can't pick up on a pattern as to which do or don't.

The driver should not be in the car. Will clarify in part A2.

I'm one of the few who have to disconnect my temp sensor. New AHC springs and a 30mm spacer didn't change my rear pressures much at all with the temp sensor connected. Disconnecting it seems to lower the pressure shown in techstream .8 last time I checked.

Per @PADDO, this is where to disconnect the temp sensor.

"It's on the side of the pump assembly, rear most connector with 2 wires, the center connector with 3 wires is your pressure and the most forward connector with the 2 heavier blue and white wires is your pump motor."

 

[wrigh003]

This forum is batting a thousand for me this week. Excellent writeup and THANK YOU SO MUCH for compiling.

 

[Moridinbg]

@LndXrsr great job! Finally everything is gathered in one place!

One advice though - I would change the places of A4 and A5. The graduations difference is irrelevant when the pressure is not right. At ~8MPa I was at less than 7 graduations. At the correct 6.9MPa I was back to between 10 and 11.

 

[LndXrsr]

Point taken. Section A is really all about just measuring, so the order doesn’t really matter too much. I do mention in A4 that you shouldn’t do anything about too few graduations from L to H until you’ve also completed parts A, B and C. Some find that fixing pressures improves their graduations, others don’t. I stayed at 8-9 before and after my process.

 

[melepley]

Great job compiling this information in one place.