Definitive list of AHC maintenance items

[LateOnTheBrakes]

If you took that nut off I don't know how to help. But I can tell you between talking to PADDO and getting a new sensor yesterday the factory/default setting of the sensor is the top of the heim joint is all the way at the bottom of the slot and there should be about 8 threads visible on either side of the middle nut on the threaded rod. It out my height right where it is supposed to be +0.1 and -0.2 in the software. 19.8" on the DS and 20" on the PS. I made the mistake of messing with the TBs first. So now my pressures are low and I'll have to correct that.

 

[Oldharoldelaney]

The nut didn't come off. It spins with the threaded shaft, perhaps due to corrosion. I can only assume that the threaded portion connects to the sensor contacts, hence the change in values as I turn it. Thanks for the info on the heim and number of threads. Mine started at the bottom of the slot, but I attempted to adjust it to be in the middle of the slot. I didn't pay attention to the length of the linkage; will double check. Hopefully we get our issues sorted soon. So much learning!

 

[LateOnTheBrakes]

There should be a little locking tab that prevents the rod from turning while you tighten it. If you torque past the 49 lb-in you may flatten the ear on the tab and render it useless. I would get a pair of needle nose vice grips and put some brass shim stock or something else softer between the jaws and the threads so you don't eff them up.

 

[uHu]

You better take the sensors off and examine the arms and shafts, and the innards.

 

[Oldharoldelaney]

You better take the sensors off and examine the arms and shafts, and the innards.

This was the right move. I discovered that the arms that attach to the sensor came unseated from the shaft key. However upon re-seating them I found that the LH sensor shaft is misaligned and now has an incorrect range of motion: [image removed]

It should be like the RH sensor: [image removed]

The only way I can tell to fix it is to somehow re-orient this black stopper piece with respect to the shaft: [image removed]

Does anyone know if that's feasible and worth the effort, or if it's new sensor time? Replace in pairs? TIA.

edit: adjustment was trivial with a crescent. progress!

 

[Oldharoldelaney]

After cross leveling with TBs, adjusting sensors such that all corners are level, and flush per paddos method, front pressure sensor reads 3mpa-g, rear 7.6, and accumulator 10.3 in TS after going from L to N. Can this be right? Do I really want to crank down the TBs to try to bring the front pressure into spec? 2006 with 128k miles all original equipment. TIA.

 

[LateOnTheBrakes]

I am in the same boat. You need to remove preload from the TBs.

 

[eurodre]

If anyone needs any ahc parts I'm selling the globes, lx springs and the pump and reservoire that go in the engine bay. PM me

 

[Oldharoldelaney]

19 turns seems like a lot to unload after reading about how these old bars sag and need to be cranked up. I'll give it a shot though, thanks.

 

[IndroCruise]

First, a personal thank you to all contributors. IH8MUD is a great resource for information and place to learn from the experiences of others around the world.

For my part, I finally found a scanner that works on the MOBD system on my 2006 HDR100R Landcruiser Sahara with AHC and 1HD-FTE turbodiesel in Australia – now 13 years old but only travelled 191,190 kilometres (118,729 miles), mine since 2008.
Techstream – what if MOBD and not OBD2?? Help requested please …

A readout on AHC pressures was taken electronically yesterday after raising from “LO” to “N” on a flat concrete floor.

The readings are not too far out of FSM specifications and IH8MUD guidance:

Front Pressure: 7.5Mpa actual (maybe 0.8MPa too high, FSM Target: 6.9+/-0.5 MPa)
Rear Pressure: 6.5Mpa actual (also maybe 0.8MPa too high, FSM Target: 5.6-6.7 MPa)
Accumulator Pressure: 10.4Mpa actual (after pump has refilled accumulator -- appears normal)

‘Sweaty’ front struts (shock absorbers) were replaced at 141,900 kilometres – Toyota Part No. 48510-60081. Rear struts are original – still appear dry. All four gas chambers (‘spheres’) were replaced for the first time recently at 183,231 kilometres with Toyota OEM parts sourced from Megazip Singapore - Part No. 49141-60010 Front and 49151-60010 Rear. This provided an opportunity for a thorough flush/bleed using Toyota AHC fluid – Part No. 08886-01805. The Volume Test now shows 14 graduations difference at the AHC tank when moving from “LO” to “HI” – up from 8 graduations before the change.

Height measurements also were taken yesterday using PADDO’s approximate method, measuring from bottom of fender to wheel hub centre. These measurements were much the same 50,000 kilometres ago, before the recent work:

Front LHS: 19.4 inch actual (PADDO recommendation: 19.75 inch)
Front RHS: 19.5 inch actual (PADDO recommendation: 19.75 inch)

Rear LHS: 20.0 inch actual (PADDO recommendation: 20.5 inch)
Rear RHS: 20.0 inch actual (PADDO recommendation: 20.5 inch)

Rake: 0.6 inch actual – if front and rear fenders are in the same line?????

The ride still seems a little firm, noticeable over joints and repairs in sealed roads. The vehicle runs on BFG A/T LT275/65R 17 tyres with all pressures set at 40 psi.

May I please request help with the following:

1. About 4 turns at 0.2Mpa per full turn clockwise on each adjuster should bring the front into mid-range of FSM specification? Will this change the rake of the vehicle?
2. Spacers or new springs should bring the rear into mid-range of FSM specification?
3. What rake is best for a comfortable ride and best steering?
4. How do I measure and set the rake? Can I assume that the fender arches are in the same line and that rake is the difference between the above measurements?
5. How should I interpret the Height Control Sensor readings and the Steering Angle reading?

FR Height Contol Sensor: -5.8mm​

FL Height Control Sensor: -4.0mm​

Rear Height Control Sensor: -9.2mm​

Steering Angle: -19.50 degrees​

​

Thank you in advance and best wishes to all!

Indrocruise

 

[uHu]

...The ride still seems a little firm, noticeable over joints and repairs in sealed roads. The vehicle runs on BFG A/T LT275/65R 17 tyres with all pressures set at 40 psi.

May I please request help with the following:

1. About 4 turns at 0.2Mpa per full turn clockwise on each adjuster should bring the front into mid-range of FSM specification? Will this change the rake of the vehicle?
2. Spacers or new springs should bring the rear into mid-range of FSM specification?
3. What rake is best for a comfortable ride and best steering?
4. How do I measure and set the rake? Can I assume that the fender arches are in the same line and that rake is the difference between the above measurements?
5. How should I interpret the Height Control Sensor readings and the Steering Angle reading?

FR Height Contol Sensor: -5.8mm​

FL Height Control Sensor: -4.0mm​

Rear Height Control Sensor: -9.2mm​

Steering Angle: -19.50 degrees​

Try with 36 psi in the tyres and see if the roughness goes away. Also, having the firmness selector set to comfy should remove some of the joints and potholes.
1: Your question indicates that you haven't read this thread religiously. The answer is: No.
2: Depends on the springs you put in and how much weight you have gained, but generally, Yes. New springs are better than spacers.
3: Standard specs, original. If changed, you have to compensate with front geometry changes.
4: You set the front and rear height according to specs. That gives the right rake.
5: For these height readings it looks like you have stopped before you got to the right height. If that's the case, the pressure readings would also be too low. You have to check a few times: Let it rest at Lo, move to N and wait 30 secs after coming to rest at N height. Repeat a couple of times and use the median values.
The steering angle indicates that the steering wheel is slightly out of straight forward.

 

[IndroCruise]

Thank you uHu.

My additional observations are listed in bullet points further below, noting the new appearance then disappearance of DTC C1751.

As you suggest, softer tyre pressures and use of the “comfort” setting do make a difference but the ride still seems firmer, more harsh, than it used to be prior to replacing the Gas Chambers (spheres).

In reply to your advices:

1. Admonishment is accepted concerning the effect of transferring weight from the AHC system to the torsion bars. I should have known or been able to work this out!

I was unable to turn the torsion bar adjusters by myself but help is on the way – then will do 4 clockwise turns on each adjuster, aiming to reduce the Front Pressure at “N” from 7.5MPa to mid-range of FSM specification.

2. New rear springs will be part of the follow-up actions, aiming to reduce Rear Pressure at “N” from 6.6Mpa to mid-range of FSM specification.

I will take actions to correct Neutral Pressures as soon as possible, aiming to eliminate high pressures and underloading of torsion bars and springs as a possible cause of DTC “C1751” which was observed yesterday but not previously – I cancelled DTC C1751 and have not been able to make it reappear in repeat tests today.

3. Understood – current aim is to return to standard specs.

4. Ditto.

5. Noted. All the physical measurements and all electronic readouts at “N” including pressures and sensor positions are the result of repeated observations – starting at “LO”, then selecting “N”, then waiting until indicator light stops blinking and the pump has stopped, then waiting with engine still running for a further 2 minutes just to be sure that lifting has finished and the vehicle has settled, then connecting to the suspension ECU and taking a reading. The readings on Saturday were very consistent. The values given then were the median values. The process was repeated yesterday and today. The median of physical measurements and electronic readouts is unchanged.

So, overall observations are:

- Vehicle has now travelled 191,190 kilometres (118,729 miles), manufactured June 2006,

- Front Shock Absorbers (hydraulic struts) were replaced with genuine Toyota parts in September 2016 by a reliable local workshop (not a Toyota Dealer),

- Gas Chambers (‘spheres’) were replaced with genuine Toyota parts in May 2019 by same workshop,

- Thorough bleeding of AHC system with genuine Toyota AHC fluid was done in September 2016 and May 2019,

- Due to Techstream difficulties, Mini ELM327 Scanner and Android App are used to read AHC ECU,

- Neutral pressures are high as recorded in previous post – Front 7.5Mpa, Rear 6.6Mpa,

- Height Control Accumulator pressure appears normal at 10.4Mpa – Accumulator volume has not been tested,

- The vehicle heights hub-to-fender are low after LO” to “N” movement is completed, as recorded in previous post – Front Left 19.4 inches, Front Right 19.5 inches, Rear 20.0 inches,

- DTC C1751 was observed yesterday and today, no other DTC’s have appeared. The DTC C1751 was cancelled, then Mini ELM327 was stopped and unplugged, engine and ignition were all turned off – then all were re-started in a new AHC test of Neutral Pressures. DTC C1751 did not reappear,

- ELM327 read-out of last AHC test today is shown below,

- Downwards movement from “N” to “LO” takes 12 seconds,

- Upward movement from “LO” to “N” takes 25 seconds,

- Upward movement from “N” to “HI” takes 15 seconds,

- During Upward movement from “LO” to “N”, AHC pump runs continuously. Initially, both Front and Rear rise together part of the way, then Front stops and Rear rises by itself, then Rear stops and Front rises by itself, then “N” light stops blinking and AHC pump stops, engine rpm rises slightly, and there is no further upward movement,

- All timings, measurements and electronic readings are the median of 3 to 5 repeats,

- Except for the slow rise, the system responds as expected when “OFF”, “LO”, “N” and “HI” AHC switches are used,

- There are no abnormal blinking lights. The normal blinking light shines when an AHC button is pressed and movement is in progress,

- The AHC pump and motor appear and sound normal but have not been tested,

- All height control sensors are intact, look fine from the outside but have not been tested nor dismantled,

- The underside of the vehicle is very clean, clear of mud, no corrosion,

- No fluid leaks are visible anywhere – front and rear Shock Absorbers (hydraulic struts) are clean and dry,

- Internal fluid clog is a possibility despite careful bleeding of the system in September 2016 and May 2019,

- The vehicle is completely unloaded, third row of seats are removed,

- Both OEM tanks are full of fuel – there are no additional tanks fitted,

- Vehicle permanently carries ARB Deluxe Front Bar (approx. 80kg) and KAYMAR Single Rear Wheel Carrier (no Rear Bar) carries the spare wheel. There is no underbody spare wheel.


I have looked at the FSM and TSB CP-3006 and also IH8MUD threads for DTC C1751, AHC pump and Height Control Accumulator.

Subject to any advice -- "first things first" – I will correct Neutral Pressures at “N” in case the occasional DTC C1751 appearance is just a time-out caused by high pressures and inability to raise the vehicle more quickly. If unsuccessful, I will seek further guidance on other matters such as Height Control Accumulator and AHC Pump.

Meanwhile, all coaching and comments are most welcome – including from all at IH8MUD.

Again, thank you in advance.

Kind regards,
Indrocruise

 

[Snow Wagon]

Hello Forum,
First off, I've done a lot of reading about AHC...
2003 LX w/ 116k miles.
Northeast SUV (NYC and Chicago based on the Carfax), but the rust isn't bad.

I've baselined my AHC, including changing fluid, and everything is within spec.

Height Reading at Normal Height at All 4 Corners (Level Ground, SUV Running):
Both Fronts 19 5/8” (1/8” High)
Both Rears 20 5/8” (1/8” Low)

Pump Test:
Under 15 seconds for L to N
15 seconds for N to H

After Initial Adjustment of Torsion Bars (2 turns each):
Front Pressure ~ 7.2 MPa
Rear Pressure ~ 6.4 MPa
Accumulator Pressure ~ 10.4 MPa

11 Graduations / Ticks on the Reservoir between L and H (before I changed fluid).

My question is about my use...
95% of the use of the LX will be trips from Denver to Keystone / Breckenridge.
100+ miles / 2 hours of mountains in each direction.
50% of my trips will be with 6 adults (~ 175 lbs per person) and 200 lbs of gear (heavy configuration).
So 2500 miles per year with 1250 pounds of people / gear.
Another 2500 miles per year with 2 or 3 adults and 200 lbs of gear (light configuration).

Should I be concerned about my AHC, especially the rear pressure, when travelling in the heavy configuration?
Should I spend money on new rear springs and / or spacers to get my rear neutral pressure to 6.0 or under, or should I be ok?

Thank you.
Tom

 

[IndroCruise]

Hello Snow Wagon,

As you can see from the avatar, I live in a different part of world where some kids still ask, "What's snow?"

Anyway, I will leave it to PADDO, uHu and experienced others at IH8MUD to answer or comment on your post above about AHC matters and hopefully my immediately preceding post as well.

You may be interested in the note found in the FSM (or could be another Toyota document) -- see attachment -- which gives some guidance at the bottom of the second page about load performance for LC100 and LX470 vehicles with AHC.

The law in your part of the world probably is different. In this part of the world, a plate attached to the engine firewall specifies that the legally allowable Gross Vehicle Mass (GVM) of my LC100 with 1HD-FTE turbodiesel and AHC is 3,260kg or 7,172 pounds, unless there have been approved modifications, new certification and new Government registration, AND a new plate attached to the firewall specifying a new allowable GVM. The modifications are well-known, but the certification and Government registration of a revised GVM is much more difficult.

Exceeding the GVM means that the vehicle is unroadworthy. Spot checks by Police are easily done with mobile scales and would result in a requirement to reduce any non-compliant excess load on the spot before the the vehicle proceeds any further. Non-compliance would lead to fines, liabilities if an accident happens, and rejection of insurance claims.

On a certified weighbridge, my empty vehicle with original tanks full of fuel, vehicle otherwise in original condition plus the heavy ARB Deluxe front bar, comes in at 2,740kg or 6,028pounds.

So about 520kg or 1,144 pounds are left for people/gear, which is not very much to play with!

When I get near this weight, and especially if there is a heavy load in the rear, I do find that the suspension drops to "LO", indicating that the AHC pressure limit has been exceeded, at least at the rear. I have compensated, as many others have done, by adding airbags inside the rear coil springs, inflated to around 15 pounds per square inch when the vehicle is loaded. In my case, these are Firestone CR5114HP, distributed here by AirBagMan -- CR5114HP - Air Suspension Helper Kit for Coil Springs - High Pressure. A US Firestone Dealer should be able to identify an equivalent product in USA. These airbags take some load off the rear part of the AHC system. Many others have preferred to fit stronger springs -- but this is not always comfortable for travel when the vehicle is lightly loaded. Whatever is done, maintaining compliance within the GVM limit on the firewall plate remains a legal requirement in all Australian States and is policed by spot checks.

Hope this helps. There may be more flexibility in your part of the world!

 

[tjb]

You may be interested in the note found in the FSM (or could be another Toyota document) -- see attachment -- which gives some guidance at the bottom of the second page about load performance for LC100 and LX470 vehicles with AHC.

Superb document, a great addition to the library.

 

[Snow Wagon]

Hello IndroCruise,
Much appreciated.
Based on the Note in the document you attached, and the screen print of the relevant part of same document below, 1261 lbs is what I'll call the beginning of the Danger Zone.
If I'll be travelling with 1250 lbs, I'm at the begging of the Danger Zone...
Based on this info, I'm thinking I should try to get my neutral pressures (both front and rear) to the low side of the allowable range.
Looks like new rear springs and 30mm spacers for me.
Thank you.
Tom

 

[hoser]

I'd probably go King springs and if that doesn't prove sufficient, add air bags for those heavy occasions.

 

[uHu]

@Snow Wagon : Hoser x2. Otherwise asking for mr Trouble to visit.

 

[Snow Wagon]

I’m concerned that the King Springs will be too much when it’s just me, my girlfriend, and very little gear.
But, I guess it’s better to be over-sprung than under-sprung when it comes to AHC?
Better to have a firmer ride when unloaded than the AHC to be overwhelmed when loaded?

 

[IndroCruise]

Personally, Mrs IndroCruise and I like the AHC/TEMS long distance cruising comfort and the flexibility to raise and lower the vehicle when required. With just two pax, we can live within the GVM limitations in Australia and also manage the comfort versus the published load limitations of the AHC system by varying the pressure in the airbags installed inside the rear springs. See attachment. When the vehicle is lightly loaded, we use a low airbag pressure, around 5 psi, just to keep the airbags inflated but carrying no load. We inflate the airbags to 10 to 15 psi (more if required, max 30 psi) when the vehicle is heavily loaded, thereby transferring some weight from the AHC system to the airbags which supplement the rear springs. This arrangement gives considerable flexibility without sacrificing the comfort or operability of the AHC/TEMS system. I enjoy the technical challenge of learning (mostly from IH8MUD) and maintaining the AHC/TEMS system and currently I am intent on returning to FSM-specified unloaded neutral pressures as my baseline. Others have taken a different view, reflecting their own needs. Some have replaced the rear springs with non-standard, heavier duty King KTRS-79 springs often mentioned, some have completely replaced the AHC system with a conventional but heavy duty suspension. If we were intent on frequent very challenging and remote 4WD trips with heavy loads in the harsher and more remote parts of Australia, probably I would look for a non-AHC vehicle, probably LC200 with GVM Upgrade to 3,800kg (8,378 pounds) – assuming that Mrs Indocruise approves the budget!! I know that she will ask why this is necessary for 2 or 3 weeks a year!! Otherwise, with the expected long life of the 1HD-FTE turbodiesel engine, our HDJ100R with AHC is a ‘keeper’ for at least another 150,000kms, until it reaches around 350,000kms (say 200,000 miles or thereabouts).