Definitive list of AHC maintenance items (1 Viewer)

[uHu]

1. Is this a 1:1 correspondence, i.e. moving 1/4 inch down lowers the rear height 1/4 inch?

2. Is it odd that I had zero issue getting the springs in in my 06 LX without doing anything other than removing the lower shock bolt? I didn't even unscrew the brake line from the attachment. I had planned to, but proceeded without by watching everything closely as I very slowly lowered the axle, nothing (brake line, breather line, height sensor) seemed even close to reaching a stress point.

1: No. If you use the ratio between the distance from the front arm bolt and to sensor bracket compared to the length of the whole arm, you get the ratio of slot movement to axle movement. I.e. the truck will move more than the distance you move the arm in the slot.

2: No. Pretty easy and standard. But when the shocks are off, it is possible to lower the axle more than those lines allow for, therefore the warning.

 

[nothappening]

My rear pressures are at 6.4 MPa, I've just ordered new rear coil springs, should I also get the 30mm spacers? How much drop in pressure can be expected from new springs alone (to my knowledge, my springs are original 12 yrs old)?

 

[uHu]

My rear pressures are at 6.4 MPa, I've just ordered new rear coil springs, should I also get the 30mm spacers? How much drop in pressure can be expected from new springs alone (to my knowledge, my springs are original 12 yrs old)?

Maybe ask an appraiser. They are good at estimating.

 

[nothappening]

Maybe ask an appraiser. They are good at estimating.

I'll take that to mean that nobody could possibly tell me. I asked because I don't want to end up under the pressure range.

 

[uHu]

Depends on what springs you have ordered, there are about 6 different to choose between; and how much your old ones have deteriorated.

 

[nothappening]

Depends on what springs you have ordered, there are about 6 different to choose between; and how much your old ones have deteriorated.

I just went with the OEM LC springs for AHC, parts:
RH: 48231-6A770
LH: 48231-6A780

I'm currently at ~6.4-6.5 MPa rear pressure with what I presume are original coils on my 2006 MY. Dealer service history mentions no coil replacement.

 

[Ron17402]

I'll take that to mean that nobody could possibly tell me. I asked because I don't want to end up under the pressure range.

From reading this thread, 30mm spacers should reduce your rear pressure by .5 Mpa

 

[06LCTrekto500K]

The front height control sensors average their delta from 0 displacement to set overall front height, so I think what you're seeing is the result of uneven torsional force (assuming you're on level ground and not loaded up). You need to get your vehicle cross level first and then front neutral pressure down to, ideally, 6.9MPa. Don't adjust your height sensors ATT. Crank the left TB up say 4 turns, crank the right down same amount (incrementally splitting the difference) go for a drive and remeasure vehicle cross level, re adjust in smaller increments as necessary. When you're cross level to less than 10mm difference fine tune your neutral pressures by cranking both up or both down the same number of turns and front height should fall into place. Hopefully you won't need trim packers for the rear, but they are cheap and easy to install if necessary.

If I have my torsions cranked all the way up currently, do I need to back the passenger side down from the drivers side? If so, about how many turns? The FSM doesn't talk about number of turns or thread differences. It says eyeball it but its not clear on how to do that, i.e. measuring device or what not.

 

[06LCTrekto500K]

From the screen shot you've posted your pressures are way high and this can't be giving you the ride quality these systems are capable of. I guess the alignment shop unloaded your front without knowing what they were doing. Don't touch your sensors at this stage. Stock height specifications are approximately 19.75 inch front and 20.5 rear, measured from fender bottom to centre of centre cap. Actual measurements are much more particular and they are detailed in the screen shot I've posted several posts up. 19.75 and 20.5 inches at the fenders is good enough. Unless your front and rear heights are somewhat different to 19.75/20.5 there is no need to touch your height sensors.

So I expect you'll just need to make sure your cross level is satisfactory (by adjusting one or possibly both torsion bar bolts if you're way off level - splitting the difference) and then adjust both bolts equally to lower your front pressure. There is one 30mm bolt on each side, one full turn CW on both bolts will lower your neutral pressure approx. 0.2MPa, so you most likely have to crank on CW 6+ turns (to increase TB tension and therefore lower hydraulic pressure) both sides to get down to 6.9 or thereabouts. Initially taking fender/centre cap height measurements (engine running and vehicle settled at N) at each wheel is necessary to understand if you're cross level and you have the appropriate front to rear rake.

Height sensors control height, not torsion bars in AHC vehicles so adjusting your torsion bars doesn't change the functional height, it does change the static height whilst adjusting with the engine off but the Active part of Active Height Control will self adjust levels/height with the engine running.

You have torsion bars at the front, their tension is adjustable via the bolts. Rear coils should to be replaced when you can't get neutral pressures down to spec (when the vehicle is at stock height/weight) which is 5.6-6.7MPa, personally I think the lower the better in this range. If your coils are original they should be replaced in all likelihood.

I've previously posted up the actual FSM pages for adjusting vehicle height and neutral pressures, search my posts under something like "AHC FSM" and you'll get hits and you should find those pretty helpful.

Hi PADDO, it is glaringly obvious you are the AHC Guru. I have been working tirelessly to diagnose my AHC. I have Techstream and have read my values. I am within spec after cranking my torsions. I have checked and have 12 graduations when I go from Low to Hi. It ungulates fine, but the road tattoos or even the lines on the road feel harsh all the way into the cab (most days). About 6 out of 7 days it drives like this. About 1 out of 7 it drives nice. I tested the ECU and according to the FSM (Page 113) with the ignition ON, if it reads between 9 - 14 Volts, it says to replace the ECU. I checked with the dealer and they want $1,300 for the part alone. I have been speaking with someone on eBay and have a deal to buy his for $150. He claims his AHC worked well and switched to OME. I did ask him if he volt tested his ECU prior uninstalling it and he did not. Thoughts on replacing the ECU to fix my issues? I can find any threads talking about replacing the ECU. The book eludes a lot to replacing the ECU if testing fails.

 

[Jczajka]

I need advice on getting my rear pressure down.


Got front pressure dialed at 6.9mpa, rear is high at 8.2mpa.

I've installed new Plaiedes globes, replaced all bushings and cushions on the shocks, and bled with Toyota fluid to get all the air out. Front height 19.75" L/R, rear height 20.5".

I have a storage platform in the back of my truck filled with two big bins of work samples and the back seat is also full for daily driving.

Seems to me new springs are the best bet. Do I install new OE Lexus AHC springs or I need something stiffer like King Springs?

@PADDO mentions that spring spacers will only reduce pressure a little bit, so it doesn't seem worth it with my 20 year old springs. I need to reduce rear pressure by 1.4-2.5 Mpa, ideally on the low side.

Anything else I'm overlooking?

Recently replaced almost everything in my front end and all bushings in the rear end of the truck, so most other variables have been removed.

Edit: attached Techstream Data

 

[trdcorolla]

I need advice on getting my rear pressure down.


Got front pressure dialed at 6.9mpa, rear is high at 8.2mpa.

I've installed new Plaiedes globes, replaced all bushings and cushions on the shocks, and bled with Toyota fluid to get all the air out. Front height 19.75" L/R, rear height 20.5".

I have a storage platform in the back of my truck filled with two big bins of work samples and the back seat is also full for daily driving.

Seems to me new springs are the best bet. Do I install new OE Lexus AHC springs or I need something stiffer like King Springs?

@PADDO mentions that spring spacers will only reduce pressure a little bit, so it doesn't seem worth it with my 20 year old springs. I need to reduce rear pressure by 1.4-2.5 Mpa, ideally on the low side.

Anything else I'm overlooking?

Recently replaced almost everything in my front end and all bushings in the rear end of the truck, so most other variables have been removed.

Edit: attached Techstream Data
View attachment 2132425

Did you unplug the AHC temp sensor when you checked pressures? Per @PADDO that's what the FSM says to do. My rear pressure goes down .8 if I remember right with the temp sensor disconnected. Yours would still be high if your pressure dropped like mine. Your rear springs are tired and have to hold up your storage platform now. Depending on the weight of the storage platform you might need be able to get by with new OEM rear springs and a 30mm spacer but that cost is close to the King springs.

 

[Jczajka]

I'll try the measurements again with the temp sensor unplugged. I read different accounts, but thought it didn't really make a difference if it was plugged in or not.

The weight is In the back of the truck, but not overly heavy, maybe a 200lbs tops.

I would think OE LX springs would be the best ride with new globes. It seems the King springs are stiffer and would ride harsher than I want. What's feedback from King spring users for daily driving and not trail/off-road use?

 

[hkeller]

Hi PADDO, it is glaringly obvious you are the AHC Guru. I have been working tirelessly to diagnose my AHC. I have Techstream and have read my values. I am within spec after cranking my torsions. I have checked and have 12 graduations when I go from Low to Hi. It ungulates fine, but the road tattoos or even the lines on the road feel harsh all the way into the cab (most days). About 6 out of 7 days it drives like this. About 1 out of 7 it drives nice. I tested the ECU and according to the FSM (Page 113) with the ignition ON, if it reads between 9 - 14 Volts, it says to replace the ECU. I checked with the dealer and they want $1,300 for the part alone. I have been speaking with someone on eBay and have a deal to buy his for $150. He claims his AHC worked well and switched to OME. I did ask him if he volt tested his ECU prior uninstalling it and he did not. Thoughts on replacing the ECU to fix my issues? I can find any threads talking about replacing the ECU. The book eludes a lot to replacing the ECU if testing fails.

I am having this exact same ride quality in my LX570. Any ideas?

 

[Jczajka]

Did you unplug the AHC temp sensor when you checked pressures? Per @PADDO that's what the FSM says to do. My rear pressure goes down .8 if I remember right with the temp sensor disconnected. Yours would still be high if your pressure dropped like mine. Your rear springs are tired and have to hold up your storage platform now. Depending on the weight of the storage platform you might need be able to get by with new OEM rear springs and a 30mm spacer but that cost is close to the King springs.

I unplugged the sensor and the specs were the same. So I definitely need new springs.

My question is should I go with OE LX AHC springs or King Springs? I have a Falken Wildpeak AT3W 275/70R18 as my spare which is 60lbs, a 1up 3 bike hitch rack that weighs ~70lbs, and the storage platform and gear that is probably 160-200lbs. So some extra weight for daily driving, but not hardcore off-road gear.

From reading some of @PADDO notes it seems rear OE springs and maybe 30-40mm spacers to bring pressure in specs with the extra weight or King springs and no spacers. Wondering what the King springs ride is for a pretty much stock truck.

 

[SlowBuild]

My stock setup was at Fr: 6.9, Re: 7.6, Acc: 10.5 following a fluid flush and some bar cranking some time earlier.

20k miles later I finally installed my King Springs and pressures changed to Fr: 6.7, Re: 4.9, Acc: 10.5 (I was a little excited and rushed into the job without first rechecking pressures to get a baseline.)

I drove around for a few hundred miles and it settled to Fr: 7.3, Re: 5.0, Acc: 10.7

I raised all three height sensors to max out the slots (gained 3/4” all around) and cranked torsion bars 6 1/2 turns. Pressures became Fr: 6.8, Re: 5.5, Acc: 10.3 (just a hair low all around).

I haven’t checked again or adjusted since it’s settled. I’m not sure why accumulator pressures keep changing. I also haven’t fully thought through why I went from about 8-9 ticks L-H up to 14 ticks but I’ll take it for now. Maybe I’m checking wrong. Anyway I plan to readjust pressures and flush fluid again when I get a chance, it’s been about 3000 miles. In any case I’m happy with where pressures are at so far (mostly stock truck). I can’t compare to new LX springs but ride is much better than my 185k old worn out springs. I don’t mind the added 3/4” height to bring pressures up though I guess I lose a bit of down travel. I can lower as necessary (or add spring spacers) as I add weight. I did not add ahc spacers.

I found PADDO’s numbers to be very accurate for predicting pressures and adjustments and it was based on these that I went ahead and made the plunge:

Front:
1 turn (torsion bars): -0.2 MPa
1” added height: +2.2 MPa

Rear:
King Springs: -3 MPa
1” added height: +0.6 MPa (stock springs)
210lbs over axle: +1 MPa (stock springs)

I hope this helps.

 

[SlowBuild]

FWIW I’ve never unplugged the temp sensor. Maybe all my numbers are high but it should be consistent and relative. I’ll try unplugging them next time.

 

[Jczajka]

@SlowBuild that does help. That's the real world review I was hoping to have.

I ordered OE AHC springs to replace my old springs.

I installed Pleiades globes on all 4 corners in June, so those are fresh and I don't carry a ton of weight over a stock truck. My thinking was with the new globes and new springs it should ride like its supposed to and I can easily add 30-40mm spacers if I need to bring pressure down more.

 

[trdcorolla]

@SlowBuild that does help. That's the real world review I was hoping to have.

I ordered OE AHC springs to replace my old springs.

I installed Pleiades globes on all 4 corners in June, so those are fresh and I don't carry a ton of weight over a stock truck. My thinking was with the new globes and new springs it should ride like its supposed to and I can easily add 30-40mm spacers if I need to bring pressure down more.

New OEM AHC springs are a good plan Your probably carrying less than 200lbs of extra weight. @PADDO also recommends adding the 30mm spacer at the same time as new coils (which is what I did). I don't have drawers or a bike rack on mine but I have sliders and a roof rack and i'm in spec. It's nice to know that once your too heavy, the King springs are available for us with AHC.

 

[Jczajka]

@trdcorolla My thoughts exactly. I'm looking at some 30mm spacers that I can just install with the springs. The little bit of extra weight I have with new springs and spacer should bring me to the low end of the preferred rear pressure range.

 

[IndroCruise]

Springing into action – KING KTRS-79 or TOYOTA 48231-6A770 -- an Australian story ….

My touring load:

85kg (187 pounds) - ARB Deluxe Bar in the front plus two ARB Intensity lights plus GME UHF radio - fixed,
25kg (55 pounds) - KAYMAR Wheel Carrier (NOT a full rear bar, too heavy) – fixed,
150kg (330 pounds) - tools, spares, recovery gear, water, WAECO car refrigerator including food – variable,
200kg (440 pounds) - Mr and Mrs Indrocruise and their baggage – variable,
109kg (240 pounds) - diesel fuel in Toyota original fuel tanks, total 145 litres when full - variable

Add these together to give an idea of the “touring payload” carried by my vehicle:

569kg (1,252 pounds) – total “payload” when touring

Add:

2,650kg (5,842 pounds) – tare weight of vehicle without accessories, fuel, passengers

To give:

3,219kg (7,018 pounds) – tare weight PLUS total “payload” when touring

This is the “everything included” total touring weight of the vehicle and is very close to:

3,260kg (7,172 pounds) – Gross Vehicle Mass (GVM) permitted for this vehicle in Australia.

Also, 572kg (1,258 pounds) is the payload at which AHC may not operate correctly, according to FSM.

My conclusions for my vehicle and my purposes:

• my “total touring weight” is close to the maximum GVM allowable in Australia for my vehicle, AND,

• my “touring payload” is close to the point at which the AHC/TEMS systems may not operate correctly per FSM – may sink to “LO”, refuse to return to “N” and refuse to lift to “HI”, AND,

• the AHC front and rear pressures will be well above FSM specification when the vehicle is in the loaded condition as listed above, leading to possible leaks at high pressure seals, shorter life of components such as globes, struts, pump, etc,

Actions taken:

• leaky front struts (‘shock absorbers’) were replaced (obtained from the local Toyota dealer) and AHC fluid was replaced,

• later, front and rear replacement Toyota ‘globes’ were fitted (obtained from MegaZip - Genuine OEM Parts From Japan, USA, UAE | Online Store - good prices) and AHC fluid was replaced,

• ‘volume test’ from “LO” to “HI” shows 14+ graduations at the AHC tank,

• front and rear heights (hub to fender) were checked, found to be close to IH8MUD recommendations,

• existing front torsion bars were adjusted to carry more load and so that AHC front pressures are within FSM specification range at “total touring weight”,

• KING KTRS-79 rear springs replaced original Toyota rear springs (Part No. 48231-6A770 - purple mark). No spacers. The new springs are same length as the original springs which were unchanged in 192,465 kilometres (119,592 miles) in 13 years and were soft and tired,

• FIRESTONE airbags have been inserted inside the new KING springs to allow for the tow-ball weight of a future trailer or camper. Meanwhile, the airbags are set at minimal 5 psi to hold shape while not towing. [An Aggregate Trailer Mass (ATM) of 3,500kg (7,700 pounds) is allowable in Australia for a trailer including all contents if the trailer has brakes operated by the vehicle – this would help spread the load while respecting the GVM limitation of the vehicle itself],

Ride experience with revised suspension:

• Mr and Mrs Indrocruise travel extensively in Australia, sometimes on unsealed gravel roads in remote parts of the country, very occasional “trails” – see avatar – but never hardcore “off-road”. Note: Australia has a land size similar to mainland USA but occupied by only 25 million people -- away from the coastline the land is relatively dry and sometimes desert-like -- many ‘main’ roads can vary from excellent multi-lane highways to rough local roads. Inevitably, distances are long – for example, from Brisbane (East coast) to Perth (West coast) is 4,216 kilometres (2,681 miles), or, Melbourne (South coast) to Cape York (Northern tip) is 3,917 kilometres (2,434 miles).

• we like as much “plush comfort” as possible in our vehicle but have accepted some compromises,

• our revised suspension gives an excellent ride when the vehicle is loaded for touring as described above. All AHC functions work as expected – AHC moves to “LO”, “N” and “HI” on command and the four selectable TEMS settings from “COMFORT” to “SPORT” work as expected. The two “SPORT” settings are excellent at highway speeds say 110 kilometres per hour (68 miles per hour), or higher when permissible. The “SPORT” settings certainly give less body roll and better cornering,

• our unloaded vehicle also is used around the suburbs of our home city of Brisbane. Here the unloaded ride is somewhat more harsh than in original stock condition but still acceptable. The difference is more noticeable at suburban speeds, say up to 60 kilometres per hour (37 miles per hour). Choosing “COMFORT” or “NORMAL” settings reduces this effect,

• if towing and heavy touring loads were not contemplated, then the more comfortable suspension compromise would have been like-for-like replacement of the original Toyota rear springs (Part No. 48231-6A770 - purple mark), plus, FIRESTONE airbags added inside the rear springs to manage some load variations,

• My current AHC readout (using a Mini ELMscan 327 dongle plus a Samsung tablet) is shown below with the vehicle in the UNLOADED condition. Note that in the unloaded condition with the KING rear springs, the rear AHC pressure is slightly lower than desirable, meaning that the damping effect is less than optimal while the spring resistance is stronger than original, so a slightly less ‘plush’ ride than original is inevitable in the unloaded condition,

Remaining Issue:

My remaining issue is that the vehicle takes 28 to 30 seconds to lift from AHC “LO” to AHC “N” while FSM suggests 10 to 15 seconds. Partial blockage somewhere? Friction between rear springs and internal airbags slowing the lift? AHC pump and/or the long cylindrical height accumulator nearing end-of-life?

Comments from IH8MUD advisors are most welcome.