2008 LC200, AHC front suspension sinks

[storegnu]

Hello, all! First post here!

I am the lucky owner of a 2008 LC200, 4,5l Diesel. The car is high milage, but very well kept. I have done all basic maintenance to it, but are stuck with one problem; the cars front suspension sinks while standing or driving. It sinks gradually and then rises up again, I can actually feel it while driving. When standing with engine shut off, the car sinks within minutes, so that the front rises visibly when the engine is started. When the front sinks, the rear rises up, as if the fluid is pushed to the rear shocks.

The other thing worth mentioning is that the former owner replaced all front suspension components, including new springs and the hydraulic central, in an effort to cure the problem. There seems to be absolutely no leaks. I have all bills and everything was done at the dealership, which I guess didn't understand the car properly.

These cars are not meant to behave this way, are they? If not what can the problem be?

I have been thinking a bit about weak front springs, but they have been replaced recently...

Hope that somebody can provide some insight in this system.

 

[NKP Garage]

You might need new accumulators/globes. Or you might just need to bleed the system.

See this thread: LX570 AHC Globe/Accumulator Replacement - https://forum.ih8mud.com/threads/lx570-ahc-globe-accumulator-replacement.1193703/

 

[storegnu]

You might need new accumulators/globes. Or you might just need to bleed the system.

See this thread: LX570 AHC Globe/Accumulator Replacement - https://forum.ih8mud.com/threads/lx570-ahc-globe-accumulator-replacement.1193703/

Thanks a lot for the answer. I would think that this was the problem myself, but the accumulators are brand new and the system is bled…

The strange this is that fluid is pushed back in the system as almost as soon as the front has been raised to the proper height and after a few minutes the pump has to start to push the front up to proper height again.

 

[tbisaacs]

Obvious question but do you have the comfort access button enabled? Truck lowers when you get out and also lowers above a certain speed.

 

[storegnu]

Obvious question but do you have the comfort access button enabled? Truck lowers when you get out and also lowers above a certain speed.

Not enabled, but thanks for thinking about it.

 

[NKP Garage]

Are you losing fluid? Any hydraulic fluid leaking from anywhere?

 

[TeCKis300]

Hello, all! First post here!

I am the lucky owner of a 2008 LC200, 4,5l Diesel. The car is high milage, but very well kept. I have done all basic maintenance to it, but are stuck with one problem; the cars front suspension sinks while standing or driving. It sinks gradually and then rises up again, I can actually feel it while driving. When standing with engine shut off, the car sinks within minutes, so that the front rises visibly when the engine is started. When the front sinks, the rear rises up, as if the fluid is pushed to the rear shocks.

The other thing worth mentioning is that the former owner replaced all front suspension components, including new springs and the hydraulic central, in an effort to cure the problem. There seems to be absolutely no leaks. I have all bills and everything was done at the dealership, which I guess didn't understand the car properly.

These cars are not meant to behave this way, are they? If not what can the problem be?

I have been thinking a bit about weak front springs, but they have been replaced recently...

Hope that somebody can provide some insight in this system.

Definitely not normal. These are not symptoms we often see so you have a different failure mode than what is commonly an accumulator failure. This sounds to me like an internal fault with a valve that's not closing/sealing a circuit. Either the valve itself or some contamination in the system.

They were on the right path to replace the central hydraulic unit.

From the system diagram, there is another critical central component called the Height Control Valve. I could see it being a culprit too and leaking front axle pressure internally leading to your symptoms.

Referenced here as the No. 1 Height Control Valve

 

[storegnu]

Are you losing fluid? Any hydraulic fluid leaking from anywhere?

No leaks.

 

[lx200inAR]

Does the front fall evenly? Or does it seem to be a bit more on the left or right? If you wait long enough, does the front fall all the way to the bump stops?

My thoughts would be that if the truck falls to the bumpstops over a long enough time, then it's most likely a leveling valve issue. If it's more of a shift from front to rear and the front doesn't fall all the way down, then it's more likely a failure of the center control module. I suspect it's also possible that it requires a certain amount of pressure to cause the leak, but any pressure in the AHC system is quite high (800-1500psi in normal operating), maybe that's not super high in typical hydraulic systems.

As another data point, you could try leaving it parked, engine off, in H (High) and see if it drops more. Leaving it in H would increase the static pressure in the system at rest. If the front dropped all the way to the same point that it drops from N, that would point towards the leveling valve. If there is still a shift, but everything is higher than when stopped at N, that would point you back at the center control cylinder.

Just some thoughts:

For reference, the height control valve(s) is a single unit with 6 hydraulic lines attached to it and the height control cylinder has 8 lines going to it. They are both mounted to the frame on the left side between the axles.

Any fluid that leaked from the height control valve would just flow back to the reservoir. You would think that only one corner would drop if you were losing fluid from one valve, but there is a gate valve between the two corners of each axle. I don't know if anyone has ever done any testing to see what the status of that gate valve is while the truck is off. If it was open, the loss in pressure would be shared across the front axle. This wouldn't be easy to do because of the difficulty in measuring the amount of fluid in the reservoir, but if you can tell if the level of the reservoir changes after sitting for a while (ie. has more fluid it it), then that certainly points towards the height control valves as well.

The center control cylinder is purely mechanical and would not care if the truck was on or off. The difference being that when the truck is running, the AHC pump can compensate for shifts from a failed control cylinder, which would then eventually result in the truck riding at a higher height than it should. Then the AHC ECU could lower everything and start the cycle over. This may or may not be noticeable while driving.

 

[bloc]

If the truck isn’t running does it fall all the way to the bump stops?

I agree it sounds like a fault with a valve.

If it does turn out to be, please take apart your old one and post pictures.

 

[storegnu]

Hi, all!

Sorry for the late reply, but I have been away for some days.

Thank you so much for solid answers!

With regards to the car, it falls evenly at the front, that would mean the right and left is falling at the same rate. It does not seem to fall all the way to the bump stops, even when parked over night. The rear rises proportionally to the front falling. If I leave it over night in H, the front will fall to about the same level and the rear will be even higher.

I can see that the height control has been changed (Part nr: 48940-60020), and also most of the other parts in the front of the car. Seems like everything up front is actually new.

 

[storegnu]

Definitely not normal. These are not symptoms we often see so you have a different failure mode than what is commonly an accumulator failure. This sounds to me like an internal fault with a valve that's not closing/sealing a circuit. Either the valve itself or some contamination in the system.

As I am new to these cars; a fully working suspension should not fall at all, even over night, right?

 

[storegnu]

They were on the right path to replace the central hydraulic unit.

I think it was actually this unit (part nr: 48940-60020) that was replaced. I guess that this is something else than the central hydraulic unit? Could it be this unit is the one that should be replaced then?

 

[lx200inAR]

in a properly functioning system you should be able to go weeks or forever, with no loss in height.

The part you listed is the height control Valve module. if you are truly getting pressure leaking between the front and rear systems and everything is plumbed properly, the center suspension control cylinder is the only shared component where that could possibly happen. It would seem you possibly have a bad seal on the piston in that unit. Normally pressure from any corner should add mechanical force to any other corner, but the hydraulic fluid reservoirs within that unit shouldn’t be linked. It sounds like you are getting blow by though. I don’t know for sure the part I linked is correct for your model, but it’s either this or something similar.

Lexus LX570 Suspension Height Control Cylinder 49081-60010 2008-2020 OEM | eBay

Find many great new & used options and get the best deals for Lexus LX570 Suspension Height Control Cylinder 49081-60010 2008-2020 OEM at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[storegnu]

Hello, all!

A last follow up on this thread;

Thanks everybody for all the good advice, this forum is as gem of information for these cars. After changing out the height control valve module, the car is now 100% again! The car does not sink at all, even when left standing for several days. Seems like it was an internal leak in the module that accounted for the leak of hydraulic fluid from the front axel to the rear.

 

[bruisecruise]

Hello, all!

A last follow up on this thread;

Thanks everybody for all the good advice, this forum is as gem of information for these cars. After changing out the height control valve module, the car is now 100% again! The car does not sink at all, even when left standing for several days. Seems like it was an internal leak in the module that accounted for the leak of hydraulic fluid from the front axel to the rear.

What part no. did you ultimately replace to fix the issue? It almost sounds like you replaced a part that had been previously replaced (48940-60020).

 

[storegnu]

What part no. did you ultimately replace to fix the issue? It almost sounds like you replaced a part that had been previously replaced (48940-60020).

Hi!

What did the trick was replacing part number: 49081-60010. It had not been previously replaced, but should have been the first part to replace, given the issue with internal leaking between the axels. Instead the dealership replaced nearly every other part in the hunt to cure the problem...