The Dreaded AHC ...

[txtortoise]

MWK... PADDO, via Mud and over the phone, has really helped me (and this community) troubleshoot AHC issues on the LX470. (I think he needs to put nuclear sub hydraulics in his signature though).

That said, the byproduct of my getting into the details of AHC was a reevaluation of my use and how much weight I intended to put on the stock vehicle and it's the approach I'm using on my new-to-me 200. I think it's something anyone that is considering an LX470 or LX570 to do...detail weight planning.

You've got about 1200 lbs of capacity to work with when the AHC is at spec, per the manual. You really need to decide if you will be exceeding that dramatically at some point, because that's what will help determine how much time/money you want to put into bringing/maintaining AHC to spec.

If you add up your weight, and common passengers, full overlanding gear and armor (Bumper @ net 150lbs, sliders @ net 60lbs, etc.) you intend to add at some point and start getting into the 1500+ range, then replacement suspension may be in your future. Trailers complicate things as that takes away 200-400 lbs of load capacity in tongue weight, and while it can be addressed with airbags, they bring their own issues.

I love my AHC and what it does, but you do have to manage to its limitations. It's ironic that I've moved beyond the backpacking stage of my life, but I'm still adding up gear weight to see what toys I can take. Doing a full overlanding load with a 3500b trailer and old globes last year probably pushed me over the edge to new rear springs this year.

I think what I really want are the shocks used by this guy... but they get way more options in Europe.
Transafrica with a Land Cruiser 200 (Diesel) - Page 2 - Expedition Portal

Bottomline, spend some low-cost time on diagnostics to truly learn where you stand, then make decisions on repair/replace.

 

[mwk]

Wow, TX thx so much very thoughtful response....I am going to try and make the AHC work without replacing anything major....Also trying to minimize paid diagnostic time. If that hits a wall, the swap will be done....But on to figuring out what the story is!

 

[Iocaine]

Never had the AHC functioning in mine. I'm removing my switch to place a little cell phone pocket in the blank spot. Looks like I have the Strutmaster kit. Not positive. Rides MUCH better than my WRX!! HaHa! Good luck.. I would roll stock as well.. But mine was already done!

 

[uHu]

Re those fault codes (DTCs): On my 2000, I had all kind of DTCs only because of a faulty rear height sensor. Sensor fixed - no more DTC. Lesson learnt: Never trust the DTCs on the AHC system.

 

[super90]

First figure out what the situation is on the current AHC system. When it works as designed and what it's designed for, it's great.

If you go conventional, you need all new torsion bars, springs and shocks. Without a doubt. I wouldn't install any used parts of this category, especially OEM, it's all worn out by then. I personally wouldn't install new OEM.....too soft. Been down that road. I ended up with OME on my TLC. Our LX is still running AHC.

Happy to discuss more. I am probably one of the few with one of each system...

 

[mwk]

So here is an update

I had a local tire place balance and rotate the tires
When I went out to the car after they were done....lot and behold the truck was higher

The led for N is now illuminated. The situation is the same. No function of of and on fir Ahc. And the adjustment does not work


The level in the tank is down. So it must have operated for a little bit


Any thoughts?

 

[mwk]

If your solenoid coils aren't open cct and the wiring/connectors check out I'd then look to the ECU outputs, if the ECU isn't sending the correct pulses (after fault codes have been cleared) to the height or main valve block solenoids then you'd consider a used replacement ECU. Having access to Techstream would help you a lot, but check the continuity of those solenoids and wiring first. If your height solenoid is open cct I've got a spare I'll loan you till you can source a used replacement
Going to conventional isn't without its own costs, but if that's ultimately what you want to do and better suits your needs then by all means do it. I just hate to see AHCs thrown out for relatively minor problems.

here is an update

I had a local tire place balance and rotate the tires
When I went out to the car after they were done....lot and behold the truck was higher

The led for N is now illuminated. The situation is the same. No function of of and on fir Ahc. And the adjustment does not work


The level in the tank is down. So it must have operated for a little bit


Any thoughts?

 

[2003lx470]

DIY Height Sensor replacement:

 

[PADDO]

This behavior implicates a failed height sensor. What happens is when you have poor or no contact in one the system will go into a fail safe mode and drop to low or level at N if there's enough pressure in the height accumulator. When the wheels were removed either a front or the rear axle was sufficiently articulated to reposition a wiper within a height sensor, enabled the cct and kick started the system so it could return to N. I've previously recommended jacking the front or rear of a vehicle stuck in low to do exactly this. I'd look towards a sick front sensor.
Check/clean each height sensor, search "Dorman" under my posts for $55 aftermarket replacements. Did you manually clear codes as per my pm of Mar 26? Get Techstream.

 

[2003lx470]

PADDO:

My 2003 LX 470 with 92k miles has a rough ride (Wife tell me this, I too noticed). Ride got smoother last year when I flush the system with new AHC fluid, . But not back to her old self. I am thinking of changing out all 4 shock and flushing the system. There are no noticeable shock leaks. I have no way to check the system other than checking the fluid levels with H/N/L. These shocks came with the truck.

What is your opinion changing out the shocks?

 

[PADDO]

Changing shocks would be low on my priority list. Certainly new shock actuators gets you new bushings and upper cushions - which is great - but new actuators won't improve your dynamic damping as that's done primarily at the damper assemblies with their globe accumulators (~remote reservoirs). Within the shock actuators are fixed orifices that throttle fluid when the actuator is stroked in compression/rebound, but there is no gas charge like a normal, sealed shock so they don't wear out like a standard shock. I'd look towards ensuring your fluid is fresh throughout the system, no entrained gasses, your neutral pressures are optimized as best you can with Techstream and that you have a good number (9+) grads on the reservoir for your L to H test. In my 03 I changed out globes at around 130k miles with 9+ grads - damping was ok/good. With new rears and 06 take offs globes with 90k on them I went to 12+ grads and damping returned to very good/excellent. I'm a proponent of getting the maintence items and user adjustable things like neutral pressures and tire pressures in order first then looking towards replacement globes etc.

 

[2003lx470]

Changing shocks would be low on my priority list. Certainly new shock actuators gets you new bushings and upper cushions - which is great - but new actuators won't improve your dynamic damping as that's done primarily at the damper assemblies with their globe accumulators (~remote reservoirs). Within the shock actuators are fixed orifices that throttle fluid when the actuator is stroked in compression/rebound, but there is no gas charge like a normal, sealed shock so they don't wear out like a standard shock. I'd look towards ensuring your fluid is fresh throughout the system, no entrained gasses, your neutral pressures are optimized as best you can with Techstream and that you have a good number (9+) grads on the reservoir for your L to H test. In my 03 I changed out globes at around 130k miles with 9+ grads - damping was ok/good. With new rears and 06 take offs globes with 90k on them I went to 12+ grads and damping returned to very good/excellent. I'm a proponent of getting the maintence items and user adjustable things like neutral pressures and tire pressures in order first then looking towards replacement globes etc.

Thanks for the advice.
Since you know so much about this system, can you please designed a system and present it to Lexus

I need to buy Techstream and find out my numbers.