LX470 AHC System Individual Parts What Are They Used For?

[400kcruiser]

I’m trying to learn more about the LX470 AHC system. Mainly would like to know the exact purpose and how these components work and how to troubleshoot them.

For example, what does the control pump accumulator do? How would you know if yours was bad?
How would you know if you had a bad valve, but not accumulator? And what does the height control valve Do?

Globes X4
Control pump accumulator
Valves X4
Height Control Valve (by the control pump

I’ve been searching and can’t find any definitions other than the usual stuff. Thanks guys!

 

[OEMGUY0720]

On an engineering perspective, the system was made of out just basic principles: supply, control and regulate pressure (and by that we mean hydraulic fluid pressures).

Globes (x4 pieces each assigned for a shock damper) - pressurized reservoir (for the hydraulic fluid) supplying each individual hydraulic fluid-filled dampers. Function is to supply in and out the fluid and is pressure-dependent (mapped and preset inside the AHC control unit)

Valves (x4) - just like any task of any valve, this shuts and opens depending on the command from the suspension control unit thru the manual and/or automatic programmed switch.

Height control switch - this acts like a “limiter” both on the highest and lowest spectrum of the vertical height dependent on the actual full compression or extension capacity of the hardware (hydraulic damper itself).

Control pump accumulator - main aka mother pump of the hydraulic fluid to supply all the 4c globes, also holds the fluid and functions as a reservoir which is a brilliant design as the “pump” itself is situated nearest where the greater volume of the fluid is located.

I hope I explained it in layman’s term.

 

[ramangain]

Search out posts by PADDO and uHu (to just name two). Combined, perhaps separately, there is an AHC Ph.D. (or two) floating is this forum.

 

[400kcruiser]

Great info! Exactly what I needed. I knew some of it but the additional info you gave me really helped. Thanks!

 

[IndroCruise]

I’m trying to learn more about the LX470 AHC system. Mainly would like to know the exact purpose and how these components work and how to troubleshoot them.

For example, what does the control pump accumulator do? How would you know if yours was bad?
How would you know if you had a bad valve, but not accumulator? And what does the height control valve Do?

Globes X4
Control pump accumulator
Valves X4
Height Control Valve (by the control pump

I’ve been searching and can’t find any definitions other than the usual stuff. Thanks guys!

In addition to earlier replies, the following may help if not already seen:

A General Description of the Active Height Control (AHC) and Toyota Electronic Modulated Suspension (TEMS) systems and how they are meant to work is given in the Toyota LC100 Factory Service Manual (FSM). The details are the same for the Lexus LX470. This 20-page description has good diagrams and explanations of each of the component parts of these systems and will answer some of your general questions. See especially the last 4 pages -- Section 6 -- which explains System Operation. It is worth printing the whole 20 pages for a careful read and later reference. This General Description is found easily at

https://lc100e.github.io/manual/
then follow the index tabs starting right at the top:
New Car Features > CHASSIS > Suspension > Active Height Control Suspension.

Other sections of the FSM are quite technical and sometimes can be a little too brief -- more explanation would have given better clarity.

A search on IH8MUD for particular topics usually will reveal insights and practical experience which are very helpful.

AHC/TEMS Diagnostics are well-covered at the same FSM link -- https://lc100e.github.io/manual/ -- via these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS

The “On-Vehicle Inspection” and “Adjustment” sections contain most of the AHC/TEMS procedures and specifications for setting up or adjusting the suspension. These are found at the same FSM link via these tabs:
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM > ON-VEHICLE INSPECTION
and
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM > ADJUSTMENT

These sections include the FSM vehicle operating height specifications. This are quite finnicky to measure. Instead, IH8MUD Members including @PADDO and others have recommended the following approximations for vehicles in as-built stock condition:

Front operating hub-to-fender distance: 19.75 inches (about 500 millimetres)
Rear operating hub-to-fender distance: 20.50 inches (about 520 millimetres)

These measurements are independent of tyre size and overall wheel+tyre diameter but will be different if the vehicle has been ‘lifted’.

Here are a few starters on your specific questions:

“For example, what does the control pump accumulator do? How would you know if yours was bad? How would you know if you had a bad valve, but not accumulator? And what does the height control valve Do?”

1. Read the relevant FSM references and IH8MUD posts to answer the general questions and understand the following suggested steps,
2. Drop vehicle to “LO”, leave engine running,
3. Open LHS front door and leave it open,
4. Press height “UP” button to initiate rise to “N” (nothing will happen while any door is open),
5. Lie next to vehicle but well clear of its up and down movement, not under the vehicle,
6. Place fingers around solenoid at the front end of the Height Control Accumulator and the pipe connections – there is a pipe from the AHC Pump and also a pipe which goes to the Control Valve Assembly which is mounted on the inner side of the same part of LHS chassis rail on which the Height Control Accumulator is mounted,
7. Close the LHS front door with the other hand – this will cause the rise from “LO” to “N” to start,
8. Listen and feel for activity at the Height Control Accumulator at the solenoid and pipe connections – continue holding and listening until the AHC Pump has stopped after it has re-charged the accumulator following the rise from “LO” to “N” (re-charge takes about 15 seconds after the rise has completed on my vehicle, others may be longer),
9. You should be able to hear and feel the Height Control Accumulator solenoid valve (SLAC) operating – it is a bit tricky because you also will hear and feel the Front and Rear Levelling Valves (respectively SLFL and SLRL) operated by their solenoids in the Control Valve Assembly,
10. Repeat these steps but instead watch the valve operation (SLAC and SLFL, SLRL) on Techstream during the rise from “LO” to “N”,
11. Carry out the Height Control Operation Test (Active Test). Note: For this test it is much easier to bridge E1 to Ts at DLC1 in the engine compartment -- this is equivalent to bridging Ts to CG terminals at DLC3 under the dashboard. Check Height Control Accumulator resistance at its connector. For these tests – see https://lc100e.github.io/manual/ then Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > C1731/31 to C1736/36 at pages DI-239 to DI-242.

LATE EDIT: Pictures added:

Height Control Accumulator -- outer side of LHS chassis rail:

Control Valve Assembly -- inner side of LHS chassis rail: