Generally the idea is equalise front end heights as close as possible with torsion bar adjusters (not Height Control Sensor adjusters -- impossible). The aim is to equalise the load carried by each torsion bar (assuming both are in similar condition) to avoid unequal suspension and steering...
Top of the line Toyota Land Cruiser Sahara vehicles marketed in Australia and manufactured in Japan were fitted with AHC/TEMS (same as LX470) only from Aug/September 2005 (the final "face-lift" version) until superseded by the 200 series in 2007. The lesser LC100 models marketed in Australia...
The Post #398 found at the link below provides an explanation of the "black clip" .....
https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-20#post-14895892
This link leads to a relevant post -- it is a long read but it covers some of your issues, especially under the sub-headings "What to do next?" and "Some notes on so-called ‘over-riding’ of the “fail safe functions”...
Frustration+++ from @suprasvobodea and posts in two threads looking for advice. You already have learned a lot about the AHC/TEMS systems on LC100/LX470 vehicles. Here a few thoughts which may help you go further ….
Summarising the situation, as I understand it:
2002 LX470 at 230k miles, Texas...
There are a few threads that deal with a frozen linkage due to age and internal corrosion in that part of the linkage which is bolted to the top of the transfer case -- and what to do about it. In my case, the transfer case was dropped to gain access, others have cut holes in the floor to gain...
The FSM-specified AHC pressures are for the vehicle with no load, no passengers, no driver, no accessories, no fittings, fuel tanks full. The FSM is done this way because it allows the manufacturer to standardise the specifications.
However, all our vehicles are different and nowadays many are...
If new OEM AHC springs, then AHC pressures are function of the weight of the vehicle and the 'ride height' of the vehicle at the "N" height setting -- more weight than stock and/or more height than stock means more AHC pressure. If Rear AHC pressure is not sufficiently corrected by a spacers...
Intermittent C1713 combined with erratic rear height behaviour as described means a definite problem in the Rear Height Control Sensor circuit, meaning any of:
the Height Control Sensor, or,
the connector, or,
the harness.
The fact that removal and re-installation fixed the problem, at least...
As mentioned by @suprarx7nut, internal visual inspection of a Height Control Sensor may give a few clues, especially if corrosion or other degradation is obvious, but visual inspection alone provides no assurance that all is good electrically, even if the internals look good. Testing is...
Mmmm -- 70 mph on the bump stops is not a good idea -- if the wheels hit a hole or a bump then there is a chance of bending or breaking something in the suspension, particularly at the front -- or even worse, losing control of the vehicle with no effective suspension. But you know all that and...
https://en.impex-jp.com/parts/new/search.html?partNo=8940760010
Yes -- USD259 + shipping is a lot to pay for a Rear Height Control Sensor but worth it for OEM reliability and longevity.
It boils down to how you want to spend your money -- maintain the AHC/TEMS or if you don’t want to get involved with that, spend more replacing AHC/TEMS with a conventional suspension.
C1751 and C1762 often arrive together and are saying that there is insufficient fluid pressure being developed...
To answer your question, I have started by attaching a twelve year old article about Torsion Bars written by IH8MUD Member @Gunney way back in 2011. It contains some good pictures and diagrams about how torsion bars work.
It maybe helpful and includes a description of torsion bar indexing...