Seems like you have done a LOT of good work and already learned a lot of things. You are in good hands with
@suprarx7nut – good idea to refresh understandings on AHC matters from his video and “Cheat Sheet”,
… and also review Post #1 and following posts in this thread started by
@LndXrsr.
Let’s start with the torsion bars ….
Yes – it would have been better to have marked everything before disassembly so that it could go back together with more confidence – but you already know all about that.
I have attached a ten year old article about Torsion Bars written by IH8MUD Member
@Gunney way back in 2011. It contains some good pictures which maybe helpful. The article is about Non-AHC Landcruisers.
Be very careful not to become confused. Ignore all the dimensions and measurements.
AHC Torsion Bars and how they work with the AHC system are different. However, I thought that some of the pictures could assist.
In the case of your Torsion Bars and how they work on your AHC vehicle, consider the following:
If both torsion bars are
“under-indexed” and equal, then there will not be enough spring effect, not enough weight carried by torsion bars, too much weight carried by AHC system, Front AHC pressure will be too high, giving poor damping and a harsh, bumpy ride quality -- and there may not be enough adjustment thread at the torsion bar adjusters to achieve correct AHC pressures.
If both torsion bars are
“over-indexed” and equal, then there will be too much spring effect, too much weight carried by torsion bars, too little weight carried by AHC system, Front AHC pressure will be too low, also giving poor damping but with a ‘springy’ ride quality -- and there may not be enough adjustment thread at the torsion bar adjusters to achieve correct AHC pressures.
If the two torsion bars are
indexed very differently, there will be an obvious ‘lean’ across the front of the vehicle when they are equally loaded. Inspect this on level ground with no driver, no load, no pax in vehicle, fuel tanks full, and with engine and AHC “OFF”. In this condition, the Gate Valves in the AHC Control Valve Assembly are open, Left and Right sides of the vehicle are connected hydraulically and are at equal pressures. If there is a ‘lean’ across the front, then it is due to unequal deflections by each torsion bar. If one front corner is low, the diagonally opposite rear corner usually will be high (unless there are some other effects – see Post #209 in this thread).
All is not lost. The situation is recoverable.
First, carry out the
‘cross levelling’ procedure per FSM – see attachment. It is assumed that the torsion bars are in good condition and have the same ‘spring rate’. The purpose of ‘cross levelling’ is to ensure that both torsion bars are carrying equal shares of the vehicle front weight at the same deflection (movement) of the torsion bar. In a vehicle equipped with AHC, ‘cross levelling’ is NOT about final height adjustment. At this stage, it does not matter what the actual hub-to-fender measurements may be
provided that they are equal.
If ‘cross levelling’ cannot be achieved because insufficient thread is available on the torsion bar adjusters due to one or other of the above consequences of incorrect fitment of the torsion bars, then removal and re-indexing of the torsion bars will be required.
Then ‘cross levelling’ must be repeated until equal front hub-to-fender heights are achieved, before proceeding further.
Next, proceed to the Height Control Sensors, and, setting the vehicle hub-to-fender heights at “N” height setting ….
Both of the following references are essential reading for much that follows in these notes:
https://lc100e.github.io/manual/ (genuine Toyota LC100 Factory Service Manual including AHC – also relevant to LX470)
Then follow the index tabs, starting at the top left of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control & Skyhook TEMS
This opens to a 20 page general description and diagrams of the Active Height Control (AHC) system and the Toyota Electronic Modulated Suspension (TEMS) system and how these systems operate.
https://lc100e.github.io/manual/, then follow these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > C1711/11 to C1713/13
which opens at Page DI-224 – suggest print all five pages of this article.
The section
and diagrams at Page DI-227 headed
“2. Check Height Control Sensor” are especially important.
A simple 4.5 volt test arrangement is described in this FSM extract and can be made up from parts acquired from an electronics or automotive shop. A multimeter suitable for automotive work also will be required.
Suggest proceed as follows:
First, check the condition of each of the Height Control Sensors. This means removing the existing Sensors from the vehicle, then inspecting the linkages for freedom of movement and absence of damage or corrosion, then removing the cover plate and gently cleaning the internals. Then electrically test the Sensor per the second FSM extract referenced above,
and also test continuity of the connector and harness
and also test the voltage supply from the harness to the Sensor.
Visual inspection alone is insufficient as faults may not be visible to the naked eye. The Sensors work in a low voltage range of about 0.45 volts to about 4.05 volts. The voltage signals the Sensors send to the ECU are easily affected by hard-to-see imperfections in the Sensors as well as wear and tear, moisture, corrosion, poor continuity at connectors and harnesses and/or low incoming voltage.
Conflicting, widely different signals from the three Sensors will cause the ECU to adopt ‘fail safe mode’ as described in the FSM extract, with or without DTC’s. Usually, this will show as widely different Height Control Sensor readings on Techstream or other scanner. In ‘fail safe mode’, AHC operation and TEMS active damping are stopped and poor ride quality is experienced in 'fail safe mode'.
Electrical testing is a ‘must do’ whenever Sensors come off a vehicle AND before installing new Sensors on a vehicle.
Much depends on the correct operation of these Sensors including their connectors and harnesses. It is imperative that they all are reliable. Otherwise, frustration, re-work and wasted time is guaranteed. Height Control Sensor problems are among the most common causes of AHC problems. Depending on the nature of the fault – such as when the Sensor is working but sending an incorrect signal – the Sensor may not throw a Diagnostic Trouble Code (DTC). If in doubt, replace the Sensor.
With ‘cross levelling’ satisfactorily completed AND after fitting tested and reliable Height Control Sensors, it is time to
- adjust the hub-to-fender ‘ride height’ of the vehicle at “N” height, aiming at Front 19.75 inches (500 millimetres), and Rear 20.50 inches (520 millimetres), and also,
- adjust the Height Control Sensors to the correct position (sometimes called the “null position”) in which the Techstream Height Sensor readings are all zero +/- 0.2 inches (or zero +/- 5 millimetres) at “N” height, as specified by FSM. [This corresponds to a signal of about 2.25 volts from the Sensors to the ECU at the “N” height position, as seen in the second FSM extract referenced above. This is the height to which the AHC system is expected to return when “N” is selected at the switch on the centre console, or, when the vehicle is auto-levelling at “N” while in motion. The ECU does this in the background by causing the Levelling Valves and AHC Pump to operate as necessary until the matching ~2.25 volt signal from the Height Control Sensors is found and the required height is achieved with the height switch in “N” position. From this, it can be imagined why the Height Control Sensors and their connectors and harnesses MUST be in good condition for reliable signals and good suspension performance!!]
How to do these two things?
Start the engine, select “N” height at the centre console switch and allow the vehicle to settle.
The Active Test (see last page of the second attachment) can be used to raise the vehicle to the desired height. This involves connecting the pins TS to E1 at DLC1 – this is the receptacle marked DIAGNOSTIC in the engine bay, usually above the Right hand wheel arch. The connector can be an unbent paper clip or similar, nothing special is required. Lights on the dashboard will blink and Techstream will record various faults -- because this connection has the effect of bypassing the controls of the AHC system. This situation will self-correct when the connector is removed later.
When the vehicle is at the required height, turn “OFF” the engine. The Levelling Valves in the Control Valve Assembly will hold the vehicle at this height (assuming all components are healthy) -- unless the engine is turned “ON” again.
Then remove the connector from TS to E1 at DLC1, then turn Ignition Key to “ON” but
DO NOT start engine (do not want AHC to attempt auto-levelling during adjustments). If the dashboard AHC light still shows “OFF”, push down on the AHC ON/OFF switch on the centre console to turn “ON” again, select “N” height at the console switch, position the laptop screen so it can be seen using a USB extension cord if that helps, (or use an ELM327 scanner and Bluetooth to a tablet with an app), all doors closed, windows open if desired. (The height selection light in the instrument panel may blink but should show solid green when the adjustments in the next paragraphs are completed).
Then with Ignition Key still "ON", Techstream still "ON", engine still "OFF", and with an eye on the Techstream screen (or other scanner screen) move the sliders on all three proven-healthy Height Control Sensors (two Front, one Rear), one by one, until all Sensor readings are as near as possible to zero, and tighten the locknut. The heim bolts also can be used (front only) but these are very fiddly.
Then pause, check all work so far, drive around the block, re-measure all work, make readjustments as necessary.
With the vehicle now at correct heights front and rear (and only when the vehicle is at correct heights as measured hub-to-fender by tape measure), operate AHC: "N" to "LO" (allow to settle), then "LO" to "N" (allow to settle, ensure pump has stopped after re-charging Height Control Accumulator). Then record AHC pressure readings Front, Rear and Accumulator -- repeat measurements say three times to be sure of reliable readings.
Then turn both of the Torsion Bar adjusters in the same direction until the Front AHC pressure in the correct FSM range is achieved, usually involves about 0.2 Mpa per full turn. The Rear AHC pressure can only be ‘adjusted’ with new OEM springs and spacers or with upgraded springs such as King KTRS-79 if consistent heavy loads or heavy fittings must be considered. The Height Control Accumulator pressure is not adjustable and should be about 10.5 MPa in the pressure test.
Finally, two more points ….
With AHC pressures correct, it is good to check overall 'globe' condition by observing the AHC Tank level at "LO" and at "HI". A difference of 14 graduations indicates that 'globes' are as new; 7 graduations indicates that it is time to replace 'globes'. 'Globes' are 'wear items' and eventually require replacement.
It is good to change the fluid regularly, say every two or three years, so as to better maintain the overall AHC system. This is an easy DIY task, well explained back at Post #1 in this thread and in the video by
@suprarx7nut and in several other good IH8MUD threads.
