The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (5 Viewers)

[IndroCruise]

Eye opening thread about BG1/BG2 damaged upstream of BI1/BI2! Gives a working idea of electrical problem-solving.

MY06LX EWD needed badly

If anyone has a link to it?, ... need to trace AHC ECU harness from ECU connectors to damping force actuators, and the connectors at ECU are not marked ... need back of AHC ECU connector view. Thx!

forum.ih8mud.com

Excellent thread from 2018 -- THANK YOU @usedname and to originators @jLB, @goldigital, @PADDO , @theophilus , @Rubibu -- I wish I had found this years ago!!

 

[IndroCruise]

EDIT: Reinstalled Techstream but I still get the same error, but I found the procedure, connecting TC to CG pins in the DLC3.

Here are my brand spankin new codes:

C1731	Front Damping Force Control Actuator RH Circuit Malfunction
C1732	Front Damping Force Control Actuator LH Circuit Malfunction
C1733	Rear Damping Force Control Actuator RH Circuit Malfunction
C1734	Rear Damping Force Control Actuator LH Circuit Malfunction
C1736	Front Suspension Control Valve RH Malfunction

I don't think these are active codes, I suspect I might have turned the car on when I had BI1/BI2 disconnected. So this was a red herring, as far as I'm concerned.

Suggest first clear the DTC’s so that you can be sure of which ones are current, not historical DTC’s from some previous condition, and then proceed from there. Your listing shows an unusual mix of DTC's and identities -- so suspect that clearing DTC's may resolve this confusion.

There are several methods to clear DTC’s:

• Use Techstream,
• Use the ‘manual’ DLC 1 method,
• Use the ‘manual’ DLC3 method

(Toyota/Lexus Special Service Tool SST 09843-18020 is a simple connector, can be replaced with any suitable alternative, including an unbent paperclip).

Method using DLC1:

Method using DLC3:

After clearing, re-start system -- suggest engine OFF, then ON and maybe drive around the block to ensure that you are looking at current DTC's.

If the DTC’s persist indicating issues at the Control Valve Assembly, then test solenoids at Levelling Valves, Gate Valves and Height Control Accumulator -- C1731, C1732, C1733, C1734, C1736 -- per attachment below.

If all components -- Height Control Sensors, Control Valve Assembly, Height Control Accumulator -- all appear healthy, then yes, it is time to look at the circuits, meaning a hunt through the possible wiring and connector issues.

To my understanding, the DTC's for the Damping Force Control Actuators should show as C1721 and C1723 -- details also attached below.

If you are sure that components are in healthy condition, then intermittent DTC's would suggest wiring breaks which may be closing and opening as the vehicle moves, causing random appearances of DTC's.

 

[uHu]

Trying new ideas here - maybe it's been checked out, but:
If there is a problem with a gate valve, you could get a symptom like yours, usedname. The gate valves have to be open in order to get both left and right side to do it's part of a height change. The level valve is between the pump and the gate valve, and if the gate valve is closed, only one side will receive pressure from the pump (or react to the change dictated by the level valve).
So, do the gate valves check ok, measured from the ahc? And do they actually work?

The gate valves are supposed to be closed only if the steering wheel angle is over 30 ? degrees AND the speed is over some low speed, can't remember which.

Another possibility is pollution in the ahc fluid, getting stuck in some valve.

Can we somehow find out which/what parameter stops the pump, or the rising of the suspension?

 

[usedname]

Suggest first clear the DTC’s so that you can be sure of which ones are current, not historical DTC’s from some previous condition, and then proceed from there. Your listing shows an unusual mix of DTC's and identities -- so suspect that clearing DTC's may resolve this confusion.

Thank you, I cleared the DTCs using DLC3, and then drove around, switched damping modes, and cycled the height. I then rechecked the codes, they have not recurred. If they happen again then I'd have to pay attention to them, but I really think it was related to running the car with BI1/2 disconnected.


@uHu I suppose that's possible... just baffled by the consistency at which it stops. But it's hard to do hypotheticals when so much of it is a black box. Certainly the valves seem to function in normal driving (limiting body roll). Perhaps @IndroCruise has some input regarding what are the conditions that allow for raising, and if any of those conditions would be liable to malfunction at a given height.

Me, I guess I better get cracking on the circuits.

 

[IndroCruise]

I finally got the 4th globe on today.

You gave me a clue when you said 2 bolts and 1 nut holding the whole assembly to the frame. I found the second bolt on top of the frame UNDER the exhaust shield.

Well I got the assembly off, put the globe in a bench vice and used a giant pipe wrench on it. Man it was on there!

Now it's all put back together and bled. I'm getting like 17 graduations. My heights are off but I'll work on it tomorrow.

You have nailed it @TreatSmash

I just thought I would add a few pictures which may help anyone else who comes this way ....

Picture credit: @Moridinbg ; Labels: @IndroCruise

Picture credit: FSM; Labels: @IndroCruise

FSM Extract: 'Globe' a.k.a. Gas Chamber in FSM -- just as described by @TreatSmash , removal of 'globe' is only done this way if it is too difficult to remove 'globe' while it is in place on the vehicle!!

Picture credit: Unknown; Labels: @IndroCruise -- shows correct order of o-ring and hard back-up ring -- both usually factory-fitted to the 'globe' before delivery -- split is intended to ease fitting of back-up ring which is made of hard brittle material, not flexible -- the gap closes when 'globe' is fitted to Damping Force Control Actuator. (Late edit: More detail about back-up rings can be found at Backup Rings | Global O-Ring and Seal - https://www.globaloring.com/backup-rings// )

 

[astrolex]

I use the OBDLink MX+ but you have to use it with your phone. It's rather inexpensive compared to the standalone devices. Most people here use techstream, but I don't have a laptop so that's a no-go for me.

Hi TreatSmash,

Do you know whether this will work for an 04 LX470? And what app do you use?

Thanks

 

[TreatSmash]

Hi TreatSmash,

Do you know whether this will work for an 04 LX470? And what app do you use?

Thanks

Yes it works with the Lexus, just search the Google Play store for obdlink.

 

[Skruf]

I'm just bumping this up again rather than starting a new thread.

I've put in all new sensors and set to zero but the hub to guard measurement is 540mm front and 530 rear.

Obviously this is way too high.

In the first post of this thread it states

"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."

As they're all new that seems unlikely.

Interestingly it also seemed to be quite high on the old sensors too.

Should I just readjust the sensors to whatever reading it takes to get the correct ride height?
Also, should I load up the car with typical use weight prior to doing it?

Also just to note, I have KTRS79 King springs in the rear and 16" 79 series LC wheels

Thanks

 

[menancyandsam]

Lengthening the HEIM joint will lower the front. It that is want you want or shortening the back will raise the rear . Shoot for about 1 inch of rake front to back.

 

[Skruf]

Lengthening the HEIM joint will lower the front. It that is want you want or shortening the back will raise the rear . Shoot for about 1 inch of rake front to back.

But then the sensors won't read zero will they?

 

[suprarx7nut]

But then the sensors won't read zero will they?

The sensors will read zero.

The heim joint adjustment changes what "zero" means, but the height sensors will always seek out "zero".

 

[Skruf]

The sensors will read zero.

The heim joint adjustment changes what "zero" means, but the height sensors will always seek out "zero".

Ahhh! Gotcha thanks

 

[Moridinbg]

@usedname I'd bet $100 your problem is the height sensors. They are precision sensors not meant to be opened or cleaned or re-assembled. There's about a 1% chance anyone is going to open a sensor, fix it and reassemble it in a fashion that actually provides reliable performance. It needs to be replaced with a new genuine OEM sensor.

Glad to be a 1 percenter

I think I win the AHC. Or Loose, I don't know, but I have seen it all now. Have had dead height sensors, have had dead pump and now time for a wire harness issue
I have a massive **** up right between BD1 and BI1/BI2/BI3. No continuity on pins 11 & 12 (L-R & L-Y), which go to the accumulator solenoid and short circuit between all other 10 pins in BD1 and on the other end in the BIs.

BD1 & BD2 are in a horrible spot, but are reachable without cutting the wheel arch - the fuel tank has to drop. In my case I had to remove the rear prop shaft too, otherwise the fuel tank would not clear. Might be a diesel thing.
Once the tank is out you can barely disconnect BD1 & 2. The hard line to the rear passenger ram (shock) and the attachment to it are in the way big time.

BD1 & 2 as viewed from the place of the fuel tank. If you disconnect the hose for the shock from the frame is a tad easier:

You can insert a screwdriver into the plastic lock and both push it down and pry the connectors apart. I absolutely could not put my hands in and have enough leverage to pry them manually. And all the connectors had already been reconnected 2 years ago, when I removed the body from the chassis.

So took my half a day to get there to find that the issue is between BD1 and all three BIs. I am glad I made a ton of photos when I had the body removed, this is how the harness goes.

So I am so out of luck. The harnesses split right around the spring bucket and are 100% unreachable without either lifting the body or cutting the wheel arch. I am not sure yet which one I prefer...

 

[suprarx7nut]

Glad to be a 1 percenter

I think I win the AHC. Or Loose, I don't know, but I have seen it all now. Have had dead height sensors, have had dead pump and now time for a wire harness issue
I have a massive **** up right between BD1 and BI1/BI2/BI3. No continuity on pins 11 & 12 (L-R & L-Y), which go to the accumulator solenoid and short circuit between all other 10 pins in BD1 and on the other end in the BIs.

BD1 & BD2 are in a horrible spot, but are reachable without cutting the wheel arch - the fuel tank has to drop. In my case I had to remove the rear prop shaft too, otherwise the fuel tank would not clear. Might be a diesel thing.
Once the tank is out you can barely disconnect BD1 & 2. The hard line to the rear passenger ram (shock) and the attachment to it are in the way big time.

BD1 & 2 as viewed from the place of the fuel tank. If you disconnect the hose for the shock from the frame is a tad easier:

View attachment 3467110

You can insert a screwdriver into the plastic lock and both push it down and pry the connectors apart. I absolutely could not put my hands in and have enough leverage to pry them manually. And all the connectors had already been reconnected 2 years ago, when I removed the body from the chassis.

View attachment 3467112

So took my half a day to get there to find that the issue is between BD1 and all three BIs. I am glad I made a ton of photos when I had the body removed, this is how the harness goes.

View attachment 3467115

So I am so out of luck. The harnesses split right around the spring bucket and are 100% unreachable without either lifting the body or cutting the wheel arch. I am not sure yet which one I prefer...

That is an amazing picture of the harness at that location and a great example of why it's so hard to diagnose wiring like that. My guess is that right at the section in green below, the harness rubs and breaks through the insulation.

If you find your wire issue I would love to see where it ends up.

And yes, I'm assuming the dude doing a full frame off restoration would have the skill, care and precision required to get those sensors apart and back together again.

 

[uHu]

....The harnesses split right around the spring bucket and are 100% unreachable without either lifting the body or cutting the wheel arch. I am not sure yet which one I prefer...

I would either lift the body or splice in a new cable bunch around the inside of the spring bucket. Anyhow, waiting to see your way out of the bog - it seems that all the solutions you end up with are good.

I will have to do something similar, as currently I have one broken connection between the valve block and the ECU. Fixed temporarily with a single conductor going straight from the valve block and forward, up the firewall and in to the ECU. The harness connecting the valve block to the ECU is overly complex and long, but going to a custom harness is also a drawback.

 

[Moridinbg]

The short was not a short at all. All damping force control actuators - finned pieces that the globes screw on - have continuity between all terminals and it is by design, according to the FSM. On each actuator there should be between 12.0 and 13.5 ohm between terminal 2 and every other terminal.
So if any actuator is connected, a lot of "shorts" pop up on the harness. Lesson learned after I cut the unreachable BD1 Always disconnect the actuators before diagnosing harness issues

One very long day later the harness is whole again. The main issue was that the B+ cable (Blue Yellow) was broken before BD1. A few other on BI1 were eiter also broken or on their last legs. Now the AHC is working again and B+ in Techstream is back to normal. Kind of, sorta. Pump works beautifully. When the hydraulics failed 25k ago it started with the pump which was depressing, considering that the pump had less than 10k km. Probably the bad connection to the valve control assembly was a factor, now it is quick, smooth and silent again.

Now I have 2 issues

• Front sensors read strange values, but linearly, not as if sensor is broken, where values are all over the place.
  • I have maxed the FR sensor length and in normal it is sitting at -20mm with the hub to fender at 54cm, which is H.
  • I have shortened the FL sensor to minimum and it is sitting at +20mm with same 54cm hub to fender. Car says it is in N
• It is rocking like a boat left to right! I can't safely drive above 80km/h. Before I fixed the valving it was a bit wobbly around 120km/h, but still perfectly drivable. Now that the system moved up and down and sits at H equivalent, it gives very Jeep death wobble vibes.
  

Sensors are peculiar. I might disassemble them to check on the contact patches on the back plates. Strange that both failed in such similar and opposite ways.
The wobble is bugging me. Is it because it is in abnormal state from the sensors or is this the globes being shot?

 

[2001LC]

"Death wobble":

Most times when we get "death wobble", it's a blown globe. By driving ~30MPH over a speed bump, one tire at a time. We can isolate blown globe. We feel "death wobble" on blown globe tire/shock. Good globe's tires/shocks, go over bump with normal suspension feel..

Front sensors spread/position adjust (spread and or position in slide) vary:

When front sensors spread, are not equal. The system uses, ones reading to set level. Your example suggest, it used the higher.

When I get these -+ readings in tech stream of height readings, to far off from 0.0- 0.2". I'll look to see if front sensors, set at different spreads from each other. Looking at where the turn buckle (TB) sit in slide, and spread of TB adjusting threaded rod. I'll adjust the slide to near bottom. With slide locking nut washer sitting square with bottom of turn buckle. I then loosen the turn buckle's threaded rod's locking nuts. So I can adjust spread, by turning turning TB fixed nut on threaded rod.
Measuring from between end of TB, where lock nuts seat. With spread of:
TB spread at 29.6mm, I get 19 9/19" fender to axle center.
TB spread at 38.5mm, I get 19 1/16", fender to axle center.
At ~35.5mm spread, I get ~19 3/16" fender to axle center.
~19 3/16" fender to axle center, is what I find all stock 100 series.

Death wobble story:
Most times when we get "death wobble vibes". It's a blown globe. By driving ~30MPH over a speed bump, one tire at a time. We can isolate blown globe. We feel "death wobble vibes" on that blown globe.

I had one, which I'd remove shocks. I found I could not compress or expand, by hand like a syringe to flush fluid through it. Which new or use, I'd always been able to, in all others 100 series. During my first test drive, "death wobble". My first thought was frozen shocks. But by driving over speed bump, one tire at a time. It isolated to one globe. R&R the one globe and all good. I suspect, not being able to hand flush either front shock. Had to do with internal seals. Likely a result of some non Toyota AHC fluid. But it has a great ride regardless, once globe replaced.

Electric fault:

Both @suprarx7nut and I have found some wiring issues. The one I had, issue with was a rear "water tight" wire harness block filled with crud. @Moridinbg you and @suprarx7nut, both help me with that one. @Moridinbg you, by posting picture of wiring on fame, body off. @suprarx7nut, by cluing me to rear 1/4 area wiring issue, wherein you found a dead wire. We both first looked a AHC CPU, as FSM tree took us down that rabbit hole.

In my case. It was a AHC shutting off, at times. I first found, sensors TB's ball frozen. Which bent and or broke TB's arms. Frozen ball joint of TB, is very common with age. I fixed the sensor, with new TB arms. All seem good. Although, after first test drive, pressure change in front. Readjust T-bars and all good. Until 3 months later, when system again would go into failsafe (OFF) at times.

Very long store short (thread around here somewhere on it). I found water tight wire housing block, was not water tight. As it turned out. Most (not always) times driven on wet HWY or undercarriage washed, system shut down (OFF). Cleaned and added dielectric grease to seal out water. No more issues.

AHC wire housing block near rear bumper, up under rear 1/4 area attach to frame.

A clue was; IG power source Voltages 11.1V & +B power source voltage 1.9V. They should at or close to same Voltage and same as battery

After wire block fix readings, note the Voltage 13.8 and 13.3 voltages (much better). Before finial tweaking of sensors for heights and T-bar for pressure

I measure spread of TB, between red lines. Adjust, by unlocking nuts at each end of threaded rod and turning center nut on threaded rod.

 

[Moridinbg]

My left TB is extended all the way to the maximum, with only a couple of threads left inside and is at the bottom of the bracket on the UCA. The RH TB is screwed all the way in and is at the top of the bracket. This way I am getting "just" -20/20mm. Otherwise it was -90/40 or something like that.

Good tip for the globe. Going to check that, it is what I suspect too. As mentioned, I did about 20k kilometers with the AHC off due to broken harness, but pressurised at N, while being at the GVM maximum - 3250kg. Sure to have put some extra strain on them.

 

[usedname]

By the way I had the 'height adjust in N is always off by -6 mm in front and -13mm in rear' earlier in this thread.

...And I fixed it by setting N height to +6 mm in front and +13 mm in rear. (In other words, I added those measurements to the default ride height.)

So now my ride height and pressures are perfect, despite the heights in N reading consistently off by that much. The damping system also works perfect.

 

[tmdvtpike]

Has anyone had an issue with the AHC fusible link (Part No.: 90982-08285) failing? About 8 months ago, my AHC system dropped to low and the "OFF" light started flashing. I inspected the fusible link and it failed. I ordered a new one, replaced it, and all was good until a few days ago when the issue occurred again. I ordered and replaced the fusible link and drove maybe 200 yards and the system dropped to low again with the "OFF" light flashing. It's possible that I missed it when looking through this thread but did not see any comments on the fusible link and what is likely to cause it to fail. My initial thought is that as with any fuse that fails, too much current is passing through it which would indicate the pump is having to work too hard which would point to the pressures being too high. The problem is I can't get the system to work to check graduations or pressures so I'm not sure what my next step is. For context the vehicle is a 2005 LX470. I have changed the AHC fluid twice during my ownership, purchased in 2010. The LX has 222,000 miles. Any words of wisdom on next steps?