ramangain
Clarksonian disciple
How full is your gas tank?
Props to PADDO's AHC fluid replacement method! (1 Viewer)
- Thread starter Clunky
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
About half tank. That's probably why huh?
ramangain
Clarksonian disciple
Maybe. Just thinking out loud honestly.
Any luck restoring your system?Stop bleeding,leave the system in low,has the car raised back up from the bump stops?I’m no expert but I’ll take a shot…
The problem is mechanical – it is not related to the AHC system. Here are a few thought starters which may help ….
- Unless you have some very unusual faults in the AHC system -- such as jammed Gate Valve(s) in the Control Valve Assembly (midway along inner side of LHS chassis rail) or a blockage in Damping Force Control Actuator(s) (where the ‘globes’ are attached) -- then the Rear Gate Valve is open when the vehicle is stationary (or being driven straight ahead) and the AHC pressure is the same on Rear Left and Rear Right. Ditto at Front Left and Front Right.
- The AHC/TEMS system on LC100/LX470 is a two-channel (Front and Rear) system – which is why only Front and Rear pressures are seen on Techstream. The system is not a four-channel system.
- Except when the vehicle turns at speed [which is when the AHC Electronic Control Unit (ECU) closes the Gate Valves connecting Right and Left sides], the system is not capable of separately varying the AHC pressures (or heights) at each of the four individual corners.
- This means that if the vehicle is stationary, then Right and Left AHC pressures are equalised, and then the only causes of side-to-side height differences are mechanical or structural faults, or wear-and-tear or incorrect adjustments of mechanical components – nothing to do with AHC nor the Height Control Sensors – which is why side-to-side height differences cannot be corrected with the Height Control Sensor adjusters.
- At the Front, this is corrected by ‘cross-levelling’ using the torsion bar adjusters per the attached FSM extract, making the heights equal within a tolerance of +/- 10 millimetres or 0.39 inches.
- IF all is true and correct in the mechanical components and in the frame/chassis, then it is impossible for the Rear side-to-side difference to exceed the same tolerance.
- Further, if all is true and correct with nothing twisted, then when one corner is high, the diagonally opposite corner must be low. Try this with a flat, stiff rectangular object such as a hardcover book or a piece of steel plate: put one end on a bench, raise the other end – it then becomes clear that pushing down one of the raised corners requires the diagonally opposite corner to raise. In other words, if the one end of the book is cross-level, then so is the other end. It is the same on the vehicle chassis (within tolerances). This is why there is only one Rear Height Control Sensor on a the AHC system on a LC100/LX470 vehicle.
However, in the practical mechanical world of hardworking 14-to-22 year old LC100/LX470 vehicles (or in any manufactured item), good as they are, nothing is quite perfect. There always are ‘tolerances’ – some may be add together, some may counter the effects of others.
Assuming that Front cross-levelling already has been done per attached FSM extract with the vehicle on flat level ground, causes of side-to-side variation must now be discovered. These may be at the Front or the Rear and one may reflect to the other, similar to the example above using a hardcover book or similar. Suggest work up from the ground to the chassis through all mechanical parts of the suspension.
So where to start? Suggest as follows ....
- Measure fender lip to ground (not hub-to-fender) all around the vehicle – this will give a rough idea of how the vehicle is sitting on its suspension. It will be rough because the body may not be bolted to the chassis exactly evenly and/or some damage or body movement may have been acquired over years.
- Better still, measure from the lifting points (marked with a square in the diagram below) on the chassis to level ground. Assuming that the chassis is not twisted, this will give a better indication.
With Front cross-levelling already done per attached FSM extract with the vehicle on flat level ground -- suggest consider a check list of all the weight-carrying wear points in the suspension capable of disturbing the way the vehicle “sits”, including the following:
- Wheels and tyres – same type, same diameter, same wear, same inflation pressure (so rolling radius is the same all round),
- All shock absorber bushes – remembering that in an AHC vehicle the shock absorbers carry part of the vehicle weight,
- Condition of Front upper and lower control arms – not bent or damaged,
- All Front upper and lower control arm bushes,
- All Torsion bar attachments to Front lower control arms,
- All wheel bearings adjustments,
- All Rear spring seats,
- Any vehicle history or underbody indications that suggest some possible cause capable of twisting the chassis itself,
- Anything else I have missed!!
Alternatively, suggest ask a good vehicle repair workshop which repairs accident damage (or maybe even a good wheel alignment workshop) to measure the vehicle and identify the cause of the problem.
In all of this beware of ‘pursuit of perfection’. There will be some variations (within tolerance) on the day the vehicle left the factory. Wear-and-tear over the following 14-to-22 years will have added further variations.
Last edited:
thank you for this. I came back from dropping off my daughter from school, parked it and measured and now the measurements are more in line. Maybe it was off yesterday (ground wasn't flat) it's definitely within tolerance now.
Sorry for the late reply but no luck with the system. Kept trying to bleed the system thinking there was air trapped somewhere but I think it's the pump. Called Lexus to see what it would cost and they quoted me 3K (yikes) for the pump assembly. Currently considering converting it now.
Fyi, the pump and motor are each about $300 shipped. $3k is likely for the entire assembly/reservoir/manifold/pump/brackets/motor/cap which is waaaaaaay more than is necessary.Sorry for the late reply but no luck with the system. Kept trying to bleed the system thinking there was air trapped somewhere but I think it's the pump. Called Lexus to see what it would cost and they quoted me 3K (yikes) for the pump assembly. Currently considering converting it now.
If you had zero problems until flush, you've almost certainly pulled in air. The fix is not a new pump. When you bleed now, are all 4 corners bleeding out perfectly liquid fluid with zero bubbles?
Pm me if you like. Happy to help. It's easy to screw up a flush and get failure to raise, but it's equally easy to correct (albeit sometimes tedious). You don't need $3k worth of work if the flush sent you down this path. That much I can be confident on.
You sir are an awesome human being
I'll definitely keep trying. In the last bleed, I did there was clean fluid with a couple of small bubbles from two of the accumulators. I stopped bleeding because I thought I was going to burn out the pump due to the high pitch sound that was coming from it every time I started the vehicle. I'll give it another shot after work tomorrow. Thank you for the advice.
That high pitched sound is generally air trapped in the pump. Sometimes it can be air from further downstream that's migrated back to the pump. Also possible it's the inlet of the pump screens clogged with gelatinous slime from old and neglected fluid and that causes some huge vacuum force on the o rings in the pump assembly, resulting in air sucking past the oring and into the pump which makes that wonderful screech.
If you're getting air out of the bleed, keep that up.
If you have Techstream, hook it up. You can monitor codes and fluid temp. Both very helpful.
I did notice there was no screen in the bottom of the reservoir which would allow any gel or sediment to be sucked into the pump.I do recall reading that someone reversed the power leads on the pump momentarily and flushed a blockage out.If the problem is air sucked into the pump causing cavitation,cracking the lines exiting the pump might be the cure.Please take these suggestions with a grain of salt.
Yeah. It's all pretty easy once the assy is on a bench.
I haven't yet taken a pump assembly out of a 100, but I did dissect one that was already removed. Be sure to buy all the o rings and grommets so you can get it all back together with fresh rubber. It's a very simple design. Not much to trip you up, provided you're slow and careful working on a clean space.
Make sure it's not air first. If it's air the pump exercise will be a fools errand.
Suggest follow the guidance from @suprarx7nut at Post #188 and #196 in this thread as the starting point.
If the symptoms described only arose during this bleeding episode and not before, then the cause is more likely to be air stubbornly remaining in the system rather than a problematic pump.
A noisy hydraulic gear pump usually means one of several things:
‘aeration’ – in which there is air trapped in the system or the pump sucks air past the pump seals,
‘cavitation’ – in which the fluid in a fluid-starved pump forms very tiny vapour bubbles - see video at Post #78. A common cause of this condition is an impeded inlet strainer or inadequate fluid supply from the tank. Eventually, cavitation can result in tiny metal particles being pulled off the metal surfaces by the low pressure of the vapour bubbles on the discharge side. The metal surfaces then look rough and the pump loses efficiency as wear takes place from this cause.
‘labouring’ – in which the pump is struggling against to too much resistance to flow – meaning the system is overloaded or the discharge strainer is impeding flow -- pre-set overpressure protection normally would operate a bypass or trip power supply to the pump motor in this situation.
‘mechanical damage’ – in which something has happened such as solid material entering the pump – examples are impurities in the fluid (particularly if fluid is re-used) or wear-and-tear debris from other components in the system. (Unlike other kinds of pumps, gear pumps particularly dislike ingesting solid particles). The motor driving the pump could be problematic – this is possible but is extremely rare, few if any reports on IH8MUD.
More detail -- much too much information!!
Troubleshooting Hydraulic Pumps - https://www.machinerylubrication.com/Read/31064/troubleshooting-hydraulic-pumps
Cavitation Explained and Illustrated
The phenomenon of cavitation consists in the disruption of continuity in the liquid where there is considerable local reduction of pressure. The formation of bubbles within liquids...
www.machinerylubrication.com
In the case of the Toyota/Lexus AHC Pump, it is a hydraulic gear pump which is small, simple, robust and of moderate pressure and low volume as these things go – compared to industrial scale hydraulic pumps such as found on construction, mining, farming or military machinery etc. As is typical of gear pumps, it works by trapping fluid between the gear teeth and ejecting the fluid on the discharge side at a high pressure developed by the power and speed of the motor driving the pump.
When we say “AHC Pump”, we mean only the pump sub-assembly, Toyota/Lexus part number 48901-60010, not the whole assembly consisting of pump, motor, manifold block, pressure sensor, temperature sensor, fluid tank, brackets.
In a AHC Pump, the two meshing gears are tiny – not much different in diameter to a US dime, 12 teeth around each gear, about three US dimes in thickness. The clearances are tiny. The passageways inside the pump are small – no bigger than the hydraulic pipe visible coming out of the pump manifold block. Two strainers are installed in the pump to arrest particles – one on the inlet side to protect the pump, one on the discharge side to prevent particles finding their way to downstream valves such as in the Control Valve Assembly and the Damping Force Control Actuators (to which the ‘globes’ are attached), etc.
Toyota/Lexus provide no details of the parts inside the AHC Pump beyond some basic information and some helpful diagrams in the AHC general information section of the Factory Service manual. See
https://lc100e.github.io/manual/ then follow index tabs
New Car Features > CHASSIS > Suspension > Active Height Control Suspension and Skyhook TEMS
Instead, Toyota/Lexus intend that the pump sub-assembly be replaced as a unit when required as a maintenance action and not disassembled – but nothing prevents a DIY mechanic from disassembling the pump for inspection and cleaning.
If you are curious about the AHC Pump, have a browse through the following thread:
AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/#post-13385888
It deals in illustrated detail with issues within the pump itself (see Posts #67 to Post#70) and the costs, parts and part numbers (see Post #81) involved in replacement of the pump sub-assembly, if you go that way. Overall disassembly is illustrated at Post #82.
Some successes with used pumps are described in the above thread but there are also some disappointments, such as at Post #80.
Note that how a used pump “looks” does not tell you much unless you have X-ray vision. It is what is inside the pump itself that counts. Personally, I was not prepared to take the risk on a used pump unless it was disassembled so that the actual dime-size gears comprising pump itself and the two strainers can be examined. Even then, I was sceptical and decided on the greater certainty of a new pump – from Partsouq in my case.
See also
AHC pump removal with pics
This is an attempt to explain how I removed and replaced the AHC pump with a few pictures to help. Tools needed are... --10 mm deep socket (for bolt under reservoir) --10mm wrench --10mm crowfoot or small 10mm ratchet would be gold for other bolt holding reservoir --fluid extractor hose and...
forum.ih8mud.com
But back to the start – pump change-out requires that the whole AHC system is bled again, several times, so it is best to be sure of a good bleeding process in the first place.
It is probably worth mentioning that the fluid in the AHC system does not really circulate – just shuffles backwards and forwards between the AHC Tank and the extremities of the AHC system. A complete ‘through flush’ as in a brake system is not possible. The raising then lowering of the vehicle is used to partially ‘pump’ fluid out of the ‘globes’ and out of the Shock Absorbers and send it all the way back to the AHC Tank -- or out through the bleeders when bleeding. The catch is that neither the ‘globes’ nor the Shock Absorbers are completely emptied in this process, so it is never a complete ‘flush’. See diagram below of the fluid flow when Levelling Valves are opened by the ECU to allow lowering. The Levelling Valves are closed when the AHC system is "OFF" -- such as when parked or when bleeding.
In addition, the solenoid valve on the Height Control Accumulator only opens on two occasions: (1) when the vehicle is raised LO to N or N to HI, and (2) when the Accumulator is being re-charged by the AHC Pump after a raise has been completed, maybe takes 15 seconds in a new system at stock weight after the green AHC height light in the instrument panel has stopped blinking (allow 30 to 60 seconds for old age, wear and tear, partial binding of mechanical suspension parts, high pressures due to excess weight carried by AHC instead of springs/torsion bars).
The excellent @PADDO method describes an economical method of bleeding the system. However, if air is suspected to be trapped somewhere – such as in the Height Control Accumulator from which it will be sent throughout the AHC system, or in the Shock Absorbers, or may shuffle backwards and forwards in the long pipelines to the system extremities but not quite making it back to bleeders or the AHC Tank – then it may take multiple bleeding cycles involving raising and lowering the vehicle and using all five (5) bleeders to succeed, making sure that bleeders always are opened and then closed during fluid outflow under pressure to prevent air ingress and that AHC Tank always has plenty of fluid.
(As an aside, a slow raise time LO to N or N to HI -- should be around 15 seconds when new but deteriorates significantly as the vehicle and its systems age – may indicate impeded pump pressure and flow due to wear or impeded strainers but may only mean that there is air in the system and it takes time to compress it, or, AHC pressures are too high and it takes longer for the pump to raise the vehicle due to excess weight being carried by the AHC system. Techstream or similar scanner capable of reading system pressures and revealing DTC’s is your friend).
Last edited:
Ok, so attempted to continue bleeding the system. Now I'm not getting anything out of the accumulator and the passenger front globe. Tried starting the vehicle and now the pump doesn't kick on at all and the off light is blinking. The reservoir still has fluid. Did I kill my pump?
No, extremely unlikely.
You almost certainly have air trapped at the pump. When the pump runs and doesn't see an immediate rise in pressure it shuts down to protect itself. If there's air, it will not see a rise in pressure as expected and it will shut itself off and flash the AHC light.
If you are willing to get Techstream (all you need is a cable and the software from the Techstream in 5 minutes thread), you can check for the specific code causing the pump inactivity and then force the pump to run which may push that air through. I expect jarring the system (entire car in this case) a little would help move the air pockets, so driving a short distance might help.
Alternatively, you could try cracking open the lines near the firewall/pump. That might let some air out and get that pump primed again.
For our own edification, how exactly did you bleed? Were you using a clear, well sealed hose at each bleeder? And did you close the bleeders immediately after flow stopped? It would be great to determine what's tripping up some people on this bleed process so we can emphasize whatever detail is needed to avoid this annoyance.
Yes, I used a new clear hose and when I first started bleeding I stopped as soon as I saw clean fluid. I would start with the driver-side rear. then go to the passenger side rear. On to the accumulator and the front driver and passenger side. After each, I would check the reservoir to see if I need to add more fluid. Now all the other times I tried bleeding I would stop few secs to a min. And I would go back and check the reservoir before starting the vehicle. In this last bleed, I had a lot of small bubbles from the rear driver side and the accumulator went completely empty after giving out a little bit of fluid.
After posting about the accumulator I went back to try bleeding again and now the passenger front has no fluid.
