My LX470 AHC woes - I'd love your help!

[BonS]

My LX470 AHC woes - Not a happy ending!

Please hang in there as this is going to be fairly long but I want to be clear about where I am in the process of fixing my AHC. I've learned a lot along the way but I'm still on the road to enlightenment!

First the facts:
2003 LX470 with AHC & 60,000 miles
Original symptom - Wouldn't raise to N or Hi but wasn't sitting on the stops
Secondary symptom - Eventually, the rear lowered to the stops, the front was within 1" of the rubber

I began doing my homework and have access to the FSM.

I removed the three sensors and they are fine with a good signal throughout their range of movement and no corrosion or leakage detected. I sealed them up and reinstalled.

I decided to replace the spheres on the damping force control actuators (because it's about that time) and I got them from Keith Bowers of B&B Syspension. They installed fine.

It took a good deal of work to get the air out of the pump and begin getting pressure but eventually I managed to do this. (If anyone wants to know the grizzly details I'll be happy to explain).

At this point I can read and reset codes blindfolded. I'm also using a digital volt meter, DVM, to monitor the hydraulic pressure at the pump.

I bled the fluid from all four accumulators and bled the height control accumulator just a little.

At this point I can put the selector in "L" and get the hydraulic pressure to spec and the pump turns off - so far so good. I then select "N" but the pressure can't get to the level required for "N". Upon selecting "N" the pump actuates, the pressure drops off somewhat (I presume that a valve has opened somewhere to allow fluid to flow into the height control accumulator) but the pressue never does get back to the maximum observed pressure that I had while in "L".

(Please don't tell me to just go to L and stay there!)

Finally, my questions:

How do you know when all the air has been bled out of the hydraulics?

I understand air bubbles etc. but what is the symptom of an AHC system with entrained air in the lines? The FSM is silent on this.

Finally, I can't find a specific procedure on bleeding the height control accumulator. Do I just use the manual height adjustment mode and bleed the height control accumulator just like the accumulators?

 

[uHu]

First guess is that your pump is not able to build up the required pressure anymore. Like worn out, or a leaking seal or something. I've heard they don't last forever, but 60k isn't much unless someone had a lot of fun raising and lowering it constantly.
But
1
Actual hydraulic pressure is best measured with a pressure gauge attached directly to the bleeder plug. They don't lie. I've never tried using a VM to check the pressure, but as far as I remember, when studying the FSM and related material, I got the understanding that that's more or less how the T0yota tester checks the pressure; by measuring the pump pressure when the actuator to one wheel is open. Using an LSPV gauge is easy and foolproof. This will of course tie up with determining whether the normal springs do their job. (Ref. Neutral Pressure)
2
I suppose you exchanged all the fluid when you replaced the spheres. Could there ever have been anything else than AHC Fluid in there? If yes, some of it could still be in the shocks. (Or ruined the pump)
3
When bleeding the system, I found it easy to get the air out, even after changing the shocks. For the accumulator bleeding, I just used the pressure that was in there once or twice. AFAIK when/if you get air in to the pump (e.g. if the reservoir runs dry) you can not get the air bled without loosening some pipe, but it sounds like you have a good grip of that bit. My understanding is that the system (pipes etc) is made such that any air would be bled at the bleeders, except for air in the pump.
Fluid is relatively cheap. Bleed it well.

 

[BonS]

Thanks for your reply. I have several cans of fluid I don't mind bleeding some more. I agree that a direct pressure measurement would be nice - if I hade the setup to get one. Only Lexus has serviced this truck and the fluid was never changed until now.

The FSM says that the AHC controller is looking for 1.48 - 1.85 volts from the pressure transducer at the pump. This is where I'm watching as I diagnose this issue. The voltage tops out at 1.845 to 1.855 volts - thats accurate! I traced this signal right to the AHC unit itself and verified the signal is indeed making its way to the input of the AHC computer.

All that being said, without any AHC trouble codes showing, I can start the engine, watch the voltage/pressure climb to the correct level and after about 20-30 seconds the AHC decides that there isn't enough pressure!

The suspension is moving but very slowly. Perhaps what I'm experiencing is a timeout by the AHC rather than low pressure.

I tried to bleed the height control accumulator a bit more but there was very little fluid flow when I opened the bleeder. Is this normal or should there be quite a bit of fluid flow? The suspension is not at the bottom but rather somewhere in between. Shouldn't the suspension drop when I open the height control accumulator? All I'm getting is a an inch or two of fluid in my clear hose. Can that be right?

 

[hkeller]

One thought. I don't think the height control accumulator will "refill"itself with weight on the front wheels. With the key in the off position, jack up the front of the vehicle so the wheels are off the ground. Then, start the vehicle with the AHC resevoir almost full to the top (you can always suck extra fluid out later). Then, push the "high" buttom and let the hight control resevoir fill. I think that may help. Let us know.

Good luck!

 

[hkeller]

BonS: Did you get it fixed?

 

[BonS]

I'm going to try your suggestion tonight or tomorrow. I'm tracing the hydraulic circuit involved in the AHC right now. I've been unable to find a complete description or hydraulic diagram so I'll make my own. As an engineer I can't stand to work on a system that I don't have a complete understanding. More soon . . .

 

[BonS]

I finished checking out the hydraulic circuit of the AHC. This is a quick rendition using "WordCad" as I call it.

I jacked up the front end, floating the front tires and then worked the hydraulics up-n-down as much as I dared while keeping a watch on the reservoir; no change in level. I then removed the jack stands and tried to bleed the height control accumulator and I hardly got a drop of fluid.

At this point I'm suspecting that there is something wrong with the height control accumulator. I talked with Keith Bowers of B&B Suspension today and he's willing to try to install a pressure fitting in it but he's never done it before. We know that this is a pre-pressurized unit and like the spheres it could have lost its charge or sprung a leak in whatever kind of diaphram it uses. I checked with my local dealer and the going price is just under $700 for a new unit. I've also sent out some feelers to find a used unit.

There is a solenoid on the height control accumulator and I still don't know its function for sure. It could be a two or three way valve. The system has to have a way to dump pressure when lowering and yet rapidly increase pressure for raising. The only way I can think that this will work is with a 3-way valve in the accumulator (so I still have some more homework to do). I can hear mine clicking when I apply 12 volts to it and its coil is about 4 ohms. I can't find any specs in the online FSM.

 

[BonS]

This can't be coincidence. I found this on an automotive rebuilders site and, no, they don't offer rebuilt AHC parts. My height control accumulator is the newer version referred to in the quote but this but the fault of the suspension "not working or rising slowly" and the reason being the accumulator failure and my accumulator not retaining pressure all suggests that there is a new height control accumulator in my future.

It seems like the new-and-improved height control accumulator may not be as improved as they thought.

Landcruiser Amazon

Fault:

Active height control suspension not working or rising slowly, fault codes C1571 and C1762 being stored.

Cars involved:

All vehicles having active height control suspension manufactured up to 25/10/2002.

Reason:

The hydraulic pump is obstructed by the broken O ring of the Height Control Accumulator.

Solution:

Check if the date of production on Suspension Height Control Accumulator is before 25/10/2002 (24X2). If so, then fit a different Height Control Accumulator (part no 49130-60010) and hydraulic pump.

</SPAN>

 

[BonS]

I've revised my hydraulic diagram one more time. I now "believe" that the height accumulator solenoid valve is a simple on/off valve and in the configuration shown and in conjunction with the Control Valve Assembly all operations can be accomplished within the 10-15 seconds normal operating times.

I've found some better prices for the height accumulator in the range of $500 new - not great but better.

I did buy a nearly new height accumulator on eBay France. How does $35 EU sound? That's only about $50 US. Yes the shipping is more than the part but only another $75. So $110 total gets it here next week.

If the replacement height accumulator fixes everything then I'm thinking that my original damping force actuator spheres that I replaced we're not the problem and I'll probably sell them cheap.

I guess it's time for a while I wait for the mail to arrive.

 

[Texasoil]

Bon and I have had a few real good discussions as he tries to get his AHC fixed.
I agree with his determination that the large 'height control accumulator' has failed.

The low volume pump simply can not put out enough to raise the vehicle in a timely manner without high pressure oil stored in this large tank. In the course of diagnosis and trouble shooting, Bon has become THE MOST KNOWLEDGEABLE about the AHC system outside of Japan where it was designed. Kudos to Bon.

Techs at the dealer would have already replaced the pump, all four shock/damping accumulators, probably a couple of shocks, the level sensors, the control valve assembly. +/-$12K and going.

I will be happy to pay shipping for the 'dead' main accumulator and the 4 old shock units. I will test the old shock units and post the remaining % of original pre-charge.

Anyone desiring to buy them would owe Bon for the price, and me for shipping costs.

Results of the post mortem on the main accumulator will also get posted here.

 

[BonS]

Aw shucks it ain't nuttin' - nuttin' because I haven't finished fixing it yet! I will take you up on your offer though so we can all benefit from this journey. (Besides, I really do want to know how the accumulator failed and how it's constructed.)

Bon and I have had a few real good discussions as he tries to get his AHC fixed.
I agree with his determination that the large 'height control accumulator' has failed.

The low volume pump simply can not put out enough to raise the vehicle in a timely manner without high pressure oil stored in this large tank. In the course of diagnosis and trouble shooting, Bon has become THE MOST KNOWLEDGEABLE about the AHC system outside of Japan where it was designed. Kudos to Bon.

Techs at the dealer would have already replaced the pump, all four shock/damping accumulators, probably a couple of shocks, the level sensors, the control valve assembly. +/-$12K and going.

I will be happy to pay shipping for the 'dead' main accumulator and the 4 old shock units. I will test the old shock units and post the remaining % of original pre-charge.

Anyone desiring to buy them would owe Bon for the price, and me for shipping costs.

Results of the post mortem on the main accumulator will also get posted here.

 

[r3run33]

hey bons you are the man with all that stuff hey in your research have you found out any info on why 06 & 07 are having so much trouble and previous years have not? what did toyota change?? my 06 lx has had lots replaced but seems to be having another problem the sytem works and no sagging but the truck sometimes lift and lowers when stopped at a traffic light. When i get home tonight i will dig out my service write up and see if the parts where listed on the 2 separate visits to the dealership

 

[uHu]

... but the truck sometimes lift and lowers when stopped at a traffic light....

1/2 inch up or down when stopping is normal. It also happens while driving, only we don't notice it. It's a result of the self leveling function. The height of the front and the rear are affected by aerodynamics while driving, hills, acceleration and braking. The Ahc is just trying to keep things level according to the conditions at the moment; also while stopped, when conditions often change in relation to conditions while driving.

 

[BonS]

Just a quick update: I received my "French" accumulator today. It looks to be in good condition - but we'll see. I began the process of removing the old one but ran into a tool shortage. I need to beg, borrow or buy 10mm and 14mm crows-foot flare nut wrenches to remove the hydraulic lines. This shouldn't be too hard with the right tools.

The bad news is that the accumulator was installed at the factory before the body went on and little thought was given to accessing the bolts on top of the truck frame. The rear bracket bolt is a bear! Everything is in the way: accumulator, body, hydraulic lines, electrical harness and gas tank. I think it took me over 2 hours and a fist full of wrenches - no two fists full of wrenches to coax this bolt out. It could have been 10mm long but nooooooo it is about 40mm! I'm sure that I'll replace it with a shorter bolt when things go back together. Oh, well, more soon.

 

[adam4x4]

I've been following this thread and just now realized you are in Blue Springs!!!

Anyways, I think I have those size flare wrenches at home if you want to borrow them. Let me know and I'll get them to you

 

[BonS]

I've been following this thread and just now realized you are in Blue Springs!!!

Anyways, I think I have those size flare wrenches at home if you
want to borrow them. Let me know and I'll get them to you

Hi Adam, yea we're neighbors! I bought what I need this morning at Clark's Tools. They're only 6-point SK's but I'm hoping I have room to swing them. If not I may be back in the borrowing mode (but I hate to pass up a tool buying opportunity).

 

[uHu]

BonS
How is your AHC doing?
Any progress?

I still think that the pump is to blame, considering that the electronics seldom go wrong in T0yotas.

For determining whether the accumulator works, I measured how much fluid comes out when bleeding.
In addition, I found that:
1 - The car does not lower when bleeding the accumulator.
2 - The amount of fluid seems to vary with conditions other than the pressure on the shocks.
3 - When bleeding, the fluid comes out at a very high pressure. It will blow the hose off the bleeder if you open too much. Then, the flow stops abruptly.
4 - The accumulator doesn't automatically fill up when starting, or when lowering. It needs some up and down before filling up.

Measuring:
First, after the car sitting overnight, I just startet it in order to lower to L. Stopped and bled the accumulator. Nothing came out. Nil, zero.
Then, after letting the pump raise it to N and then H, I lowered it to L again, stopped and bled. Got 160 ml (5.5 oz)
In positon N, and after making sure that the accumulator was filled (you can see it from the fluid level in the reservoir) I bled again. Got 250 ml (8.5 oz)
In position H, I got 190 ml (6.5 oz). This is less than in N, maybe the accumulator wasn't filled to max pressure? Maybe the speed of bleeding, i.e. how much you open the plug, affects the amount?

Did you get the new accumulator installed OK?

 

[BonS]

BonS
How is your AHC doing?
Any progress?

Yes, some. I installed the new accumulator. Those bolts on top of the frame are no fun at all!! In the process of having the system open I lost the fluid in the reservoir and, of course, got air in the pump and lines.

I still think that the pump is to blame, considering that the electronics seldom go wrong in T0yotas.

I have been comming to the same conclusion. Part of what has led me to this is that the pump has so much trouble operating at low pressures. Again, I've been doing some more homework: The pump design is an external gear pump and this style pump in self-priming. I shouldn't be having as much trouble as I am at getting this pump to build pressure.

For determining whether the accumulator works, I measured how much fluid comes out when bleeding.
In addition, I found that:

1 - The car does not lower when bleeding the accumulator.

This makes sense as the accumulator is isolated from the system unless the solenoid is activated by the AHC controller.

2 - The amount of fluid seems to vary with conditions other than the pressure on the shocks.

This is interesting. I don't know what to make of it though.

3 - When bleeding, the fluid comes out at a very high pressure. It will blow the hose off the bleeder if you open too much. Then, the flow stops abruptly.

The height control accumulator bleeder is ported to the accumulator itself but not to the system hydraulics (when the solenoid is inactive). The internal gas pressure of the accumulator is responsible for the energetic discharge and when the internals (TBD) reach their travel limit the pressure ceases.

4 - The accumulator doesn't automatically fill up when starting, or when lowering. It needs some up and down before filling up.

I may be this up-and-down requirement that I was interpreting to be a faulty accumulator because I was getting no fluid at all from the accumulator evern after one or two -slow- height adjustments from fully up to fully down.

Measuring:
First, after the car sitting overnight, I just startet it in order to lower to L. Stopped and bled the accumulator. Nothing came out. Nil, zero.
Then, after letting the pump raise it to N and then H, I lowered it to L again, stopped and bled. Got 160 ml (5.5 oz)
In positon N, and after making sure that the accumulator was filled (you can see it from the fluid level in the reservoir) I bled again. Got 250 ml (8.5 oz)
In position H, I got 190 ml (6.5 oz). This is less than in N, maybe the accumulator wasn't filled to max pressure? Maybe the speed of bleeding, i.e. how much you open the plug, affects the amount?

Great information! I'll be watching for this as I bleed my system - and hope to add some additional measurements.

I did order an AHC pump subassembly. This is only the hydraulic pump and o-rings. The cost is not tooooo bad at just over $200; especially when compared to replacing the entire pump assembly. It should be in next week. Ahhhhh, more quality time with my ride!

 

[BonS]

Well, this update has been a long time in coming. I received and installed the AHC pump subassembly. I hit it with 12 volts while holding my finger over the outlet and WOW what a difference. It was immediately apparent that this unit primed and pumped without any problems at all. My old pump wouldn't do this, period. Keep in mind that I'm a 5-10% user of this truck as it's my wife's ride. It's only when I'm driving that anyone ever uses the height controller to lower the truck to help passengers get in and out. (My wife and daughter are both about 5' tall.) This truck has only about 50K miles and this darn pump is already worn out.

I'm sending the damping accumulators and height accumulator to Keith Bowers of B&B Suspension for evaluation. If the damping accumulators are good I'll be reselling them as used.

Since I don't have a pressure gauge & fittings to measure the output of the pump I continue to use the pressure transducer output that is attached to the pump body as a measure of pressure. My old pump struggled to get up to pressure and topped out at 1.85 volts as I stated in a previous post. The new pump measures 2.15 volts at the transducer and gets there very quickly. This is a non-invasive way to evaluate the pumps output and very quick and convenient.

The job of replacing the pump sub-assembly is quite simple quick.

I disassembled the pump sub-assembly and found nothing. No contamination, no obvious failure mode. My best guess is the the side clearance of the gears grew to be too great and the "blow-by" was just too much.

I don't think I'll be using the height control switch any more as I don't think the pump is durable enough.

 

[Joe422]

BonS... this is the closest thread I could find regarding my AHC issues.... It's been over a year since you last posted on this thread... is everything perfect?

I'd really like to know if this solved your issues....

Thanks!