AHC pump overhaul
- Thread starter MARK'S92
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Most I've seen just replace it entirely with an oldman Emu setup to avoid the headache of failure entirely...but then you miss out on that buttery smooth ride on a working AHC system
Was the ahc pump/reservoir leaking as the main reason for overhaul? Or screeching sound is still evident after ahc fluid drain and fill?
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- #4
Never a leak, only issue I’ve ever had was sensor lever breaking.
It stopped raising vehicle in timely manner, never had bouncy ride or hard ride. Now it just doesn’t raise at all, system flashing. Pump straining.
Fluid is dark, I’ve owned it for 20 k miles. 7 yrs.
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- #5
Haven’t flushed fluid, should try that first?
Definitely 
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- #7
If there is a clog you feel new fluid would solidify any sludge?Definitely
IndroCruise
SILVER Star
From previous Posts by @MARK'S92, it seems like this is a 25 years old 2001 LX470, based in Boston? So underbody may have some effects of snow/salt/debris affecting/corroding AHC components (especially Height Control Sensors) and/or AHC pipework and/or AHC wiring harnesses?? If these are all in good condition, then rehabilitating the Active Height Control (AHC) system and Toyota Electronically Modulated Suspension (TEMS) system is easy and inexpensive. If not, then the work is more difficult and changeout to a conventional suspension may be worth considering, although this is expensive.
Symptom Descriptions:
The flashing AHC light and vehicle refusal to rise says that
+Repair Manual
+DIAGNOSTICS
+ACTIVE HEIGHT CONTROL & SKYHOOK TEMS
[Note: LX470 and LC100 use the same AHC and TEMS systems -- fitted on all LX470 and fitted as an option on some LC100 vehicles in some markets].
The noisy AHC Pump indicates either
Dark AHC Fluid indicates this situation:
It is hydraulically impossible for bleeding or change-out of AHC Fluid to dislodge blockages in the fluid strainers because the blockages are held in place by Pump pressure and the debris or gel is unable to escape past the fine weave of the material forming the strainers.
Attempting to reverse the direction of fluid flow (by reversing the polarity at the Pump Motor to reverse the direction of rotation of the AHC Pump as some may suggest) cannot help because returning fluid DOES NOT pass through the gears of the AHC Pump sub-assembly Part Number 48901-60010. Returning AHC Fluid is diverted by the Return Valve directly to the AHC Tank, not through the gears of the Pump. This is not changed by reversing polarity at the AHC Pump Motor. All that can happen then is that the AHC Pump rotates in reverse and 'churns', while AHC Fluid passes above and below the gear sides and/or passes through clearances around the gear carriers, then through the bypass strainer within the Pump, then back to the Inlet side of the gears in the AHC Pump. AHC Fluid cannot be drawn from the AHC system because the Levelling Valves in the Control Valve Assembly remain closed (unless directed to open by the ECU) -- this 'locks' the fluid in the 'globes' and 'shock absorbers'. In other words, the fluid short-circuits inside the AHC Pump if the Motor polarity is reversed. In this situation, pressures of trapped Fluid between geat teeth are extremely high, and the Pump will be extremely noisy due to cavitation and possible Pump damage
IF the conclusion is that the fault lies INSIDE AHC Pump sub-assembly Part Number 48901-60010, then this Part can be removed, dismantled and the strainers cleaned, gears and clearances inspected and the Pump re-assembled EXACTLY as found, with close attention to correct, not overlapping, fitment of o-rings and back-up rings at the gear carriers, and then all re-installed, OR, new Part Number 48901-60010 can be purchased from IMPEX (USD98.24) or PARTSOUQ (USD183.79 -- add taxes/tariffs/shipping.
For reliability and to avoid re-assembly errors, and given that the existing Pump is ~25 years old, replacement rather than repair is recommended IF the Pump is the cause of the current issues.
Pictures and discussion of issues related to the AHC Pump can be found at the link below, and links within this link, including pictures of Pump removal, disassembly and reassembly. The Return Valve also is discussed.
Symptom Descriptions:
- "The pump makes loud screeching sound, possibly straining for oil flow",
- "Now it just doesn’t raise at all, system flashing. Pump straining. Fluid is dark",
The flashing AHC light and vehicle refusal to rise says that
- the AHC/TEMS systems are in "Fail Safe Mode" (see link below) which prohibits operaton of these systems, and,
- there is at least one DTC present, possibly several -- such as C1751 - AHC Pump & Motor Circuit; C1762 - Fluid Pressure Abnormality (Pump & Motor Does Not Supply Fluid); C1763 &C1764 - Fluid Pressure Abnormality (Valve Does Not Open); C1711, C1712, C1713 - Height Control Sensor Circuits.
+Repair Manual
+DIAGNOSTICS
+ACTIVE HEIGHT CONTROL & SKYHOOK TEMS
[Note: LX470 and LC100 use the same AHC and TEMS systems -- fitted on all LX470 and fitted as an option on some LC100 vehicles in some markets].
The noisy AHC Pump indicates either
- "Aeration in AHC Pump" -- air has entered the system as a consequence of repairs and/or inadequate bleeding, or, AHC Fluid level has fallen too low in AHC Tank (cause to be identified) and air has entered via the Tank, or, air has been drawn passed the seals enclosing, and OUTSIDE, AHC Pump sub-assembly Part Number 48901-60010, OR,
- "Cavitation in AHC Pump" -- AHC Pump is unable to draw AHC Fluid from the AHC Tank due to blocked internal strainers (especially the Inlet strainer) INSIDE AHC Pump sub-assembly Part Number 48901-60010, OR,
- "Blockage of Return Valve" -- AHC Pump is unable to deliver AHC Fluid due to a blocked strainer inside the Return Valve contained in the housing separating the AHC Pump and AHC Motor -- Part Number 48905-60010.
Dark AHC Fluid indicates this situation:
- AHC Fluid has not been changed regularly as recommended in Owner's Manual -- each 60,000 miles or 6 years (or preferably twice as often for good 'hydraulic hygiene') -- and accumulation of debris or gel is now firmly fixed in the strainers mentioned above (see also pics at link referenced far below),
- A lengthy explanation can be found at the link immediately below concerning how air in hydraulic fluid due to air ingress (note the AHC Tank has a lid but is still open to atmosphere) not only diminishes hydraulic performance due to spongey effects due to aeration and potential cavitation damage at pump parts and valve orifices but also degrades the actual fluid itself through fluid breakdown, formation of sludge etc.,
- These effects generally highlight the importance of 'hydraulic hygiene':
Removing Entrained Air in Hydraulic Fluids and Lubrication Oils - https://www.machinerylubrication.com/Read/373/entrained-air-oil-hydraulic. - The AHC Fluid -- Toyota/Lexus Part Number 08886-01805 -- is a light mineral oil with additives -- no other fluid should be used in the AHC/TEMS systems without clear documented proof of comparable properties.
It is hydraulically impossible for bleeding or change-out of AHC Fluid to dislodge blockages in the fluid strainers because the blockages are held in place by Pump pressure and the debris or gel is unable to escape past the fine weave of the material forming the strainers.
Attempting to reverse the direction of fluid flow (by reversing the polarity at the Pump Motor to reverse the direction of rotation of the AHC Pump as some may suggest) cannot help because returning fluid DOES NOT pass through the gears of the AHC Pump sub-assembly Part Number 48901-60010. Returning AHC Fluid is diverted by the Return Valve directly to the AHC Tank, not through the gears of the Pump. This is not changed by reversing polarity at the AHC Pump Motor. All that can happen then is that the AHC Pump rotates in reverse and 'churns', while AHC Fluid passes above and below the gear sides and/or passes through clearances around the gear carriers, then through the bypass strainer within the Pump, then back to the Inlet side of the gears in the AHC Pump. AHC Fluid cannot be drawn from the AHC system because the Levelling Valves in the Control Valve Assembly remain closed (unless directed to open by the ECU) -- this 'locks' the fluid in the 'globes' and 'shock absorbers'. In other words, the fluid short-circuits inside the AHC Pump if the Motor polarity is reversed. In this situation, pressures of trapped Fluid between geat teeth are extremely high, and the Pump will be extremely noisy due to cavitation and possible Pump damage
IF the conclusion is that the fault lies INSIDE AHC Pump sub-assembly Part Number 48901-60010, then this Part can be removed, dismantled and the strainers cleaned, gears and clearances inspected and the Pump re-assembled EXACTLY as found, with close attention to correct, not overlapping, fitment of o-rings and back-up rings at the gear carriers, and then all re-installed, OR, new Part Number 48901-60010 can be purchased from IMPEX (USD98.24) or PARTSOUQ (USD183.79 -- add taxes/tariffs/shipping.
For reliability and to avoid re-assembly errors, and given that the existing Pump is ~25 years old, replacement rather than repair is recommended IF the Pump is the cause of the current issues.
Pictures and discussion of issues related to the AHC Pump can be found at the link below, and links within this link, including pictures of Pump removal, disassembly and reassembly. The Return Valve also is discussed.
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The specific ahc fluid or any hydraulic fluid don’t sludge even at 500k miles + the countless heat cycles, not with the operating temperatures of the AHC system. Unless the reservoir shows obvious heavy dirt contamination which you can visually see or better yet use a long cotton swab to collect a sample in the ahc fluid reservoir. Hopefully not the case and a simple DIY inexpensive ahc drain and fill will fix the issue.
IndroCruise
SILVER Star
500k miles?? Mmmmm -- maybe luck would hold that long, or may be not -- and not in accord with my experience with industrial hydraulics. The link in the late edit at Post #8 this thread and elsewhere gives some independent indication. A few pics attached below from various IH8MUD Members show some different and very real experiences. This kind of sludge accumulates in regions of the system where fluid flow may be low or slow, expecially the region behind the cover surrounding AHC Pump sub-assembly, bottom of 'shock absorbers', etc, etc. This sludge is not helpful when it breaks away and lodges in strainers, expecially the Inlet strainer within the AHC Pump sub-assembly, or in strainers and orifices elswhere ....
Keep AHC OFF, until pump works.
I've seen many. Reservoir so stained, from old dirty fluid that was never flushed. They look like they have fluid, due to staining, but actually can't be read.
Hack: Put a flash light behind reservoir. Then check level, may be revealing.
If fluid below low line, in N. When on a slope or rise to H. Pump runs dry. Run it dry enough, it burns up the pump.
You can just add AHC fluid and see if pump then works. If reservoir very dirty. Best to, first remove reservoir and clean, installing new grommet.
Another issue from around 2001. Was some of the 1L plastic bottles of Toyota AHC fluid, had a jell in them. The jell clogged systems badly. Toyota never took responsibility for this. They just bought back the 2.5L tins. A tell jelled fluid was used. The screen under cap has jell, clogging it.
Warning: Filter AHC from plastic bottles. If jell found discard. Some will use once jell filtered out. Best not to, if have a choice.
Most that try and rebuild pumps. Aren't meticulous enough, to get a working pump in the end. So for those. A used or new pump, may be the way to go.
I've seen many. Reservoir so stained, from old dirty fluid that was never flushed. They look like they have fluid, due to staining, but actually can't be read.
Hack: Put a flash light behind reservoir. Then check level, may be revealing.
If fluid below low line, in N. When on a slope or rise to H. Pump runs dry. Run it dry enough, it burns up the pump.
You can just add AHC fluid and see if pump then works. If reservoir very dirty. Best to, first remove reservoir and clean, installing new grommet.
Another issue from around 2001. Was some of the 1L plastic bottles of Toyota AHC fluid, had a jell in them. The jell clogged systems badly. Toyota never took responsibility for this. They just bought back the 2.5L tins. A tell jelled fluid was used. The screen under cap has jell, clogging it.
Warning: Filter AHC from plastic bottles. If jell found discard. Some will use once jell filtered out. Best not to, if have a choice.
Most that try and rebuild pumps. Aren't meticulous enough, to get a working pump in the end. So for those. A used or new pump, may be the way to go.