OK, I finally got Techstream to work and I found some codes.
I also tried moving it up and down and it seems to work fine for right now.
I am wondering about my rear pressures. The front pressure seemed to vary between zero and a high of 11 or so in HIGH setting.
I carry quite a bit of weight as I have the rear seats removed and I have a carpentry business worth of tools in the truck which probably weighs less than 500 pounds and I don't currently have my spare tire mounted.
Do you think I just may need new rear springs or can we ascertain from the data here to suggest a further problem? I am a fairly decent shade tree mechanic but this system is new to me so I appreciate your patience if I sound like a noob.
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Congratulations on getting Techstream running -- that is an achievement in itself!!
Thank you for posting the Techstream screenshots -- it helps to see the whole page, including ALL of the detail in addition to the pressures.
References to useful FSM links can be found in my Post #4 in this current thread, not repeated in this post. May I refer you especially to the "AHC General Description" and the AHC part of the “Diagnostics” section?
Not mentioned in Post #4 but may I also suggest scrolling down to the “Electrical Wiring Diagram” (EWD) section in
LC100 Workshop Manual - https://lc100e.github.io/ and exploring your model year there? Be a little wary -- this is an LC100 reference, not an LX470 reference and there can be some differences in detail. However, the Active Height Control (AHC) system and the integrated Toyota Electronic Modulated Suspension (TEMS) are common across “100 series” on all LX470 and LC100 models (where fitted).
This response is too long – caused by a lot of cut-and-past taken from elsewhere!!
Anyway, dealing with some of the issues arising ….
On Diagnostic Trouble Codes (DTC’s) generally:
First, suggest cancel all of the DTC’s using Techstream -- or do this manually by disconnecting and reconnecting the battery -- and see what DTC’s return. The idea is to eliminate any old and irrelevant codes in the ECU memory, ensure current codes are identified, and work from there.
AHC Pressures:
The Front AHC pressure is incredibly low at 0.1Mpa.
The Rear AHC pressure is way high at 10Mpa.
If not already done, suggest do at least three tests to be sure of consistency in the numbers -- allow plenty of time for the AHC Pump to finish its business and become silent well after the green AHC light on the dashboards stops blinking. Then record the screenshot.
Also suggest timing the raise from "LO" to "N" a few times -- (1) timing the interval between raise start and when AHC green light stops flashing on the dashboard (means vehicle is raised), and, (2) timing the interval between when the vehicle is raised (green light stops flashing) and when the AHC Pump stops (means Height Control Accumulator is re-charged) -- this
may give a preliminary indication of AHC Pump performance or hint at blockages in the system or other aberrations including harness problems.
Taken together with the reported DTC's C1736 and C1764 and the reported noise, the "AHC Pump" and "harness and connector issues" may have to go on the "list of suspects.
Vehicle Weight and AHC Pressures
The FSM specifies checking AHC pressures with vehicle empty, meaning no passengers, no added load, on a level surface, steering straight ahead (not 173.25 degrees as on the screenshot), fuel tanks full.
All good stuff. The purpose of that specification is to ensure that the AHC pressure checks and consequent adjustments are made with the vehicle in the same ‘standard’ condition every time, so that change (inevitable AHC pressure increase) over time (years) can be observed and so that numbers are comparable with FSM-specified numbers.
The AHC system itself is not adjustable. It is the mechanical part of the suspension which is adjusted or modified to accept more or less permanent load while leaving the AHC system performing the same duty.
As a practical matter, rather than stick to the FSM 'standard', it works well for AHC-related checks and adjustments to be done on the vehicle carrying whatever load it would mostly carry on a consistent basis. So the weight of persons, load, accessories and fittings does not matter
provided the checks and adjustments are done with the vehicle in the same condition every time. You can be in or out of the vehicle but is best to adopt the same procedure every time. Then matters such as torsion bar adjustments and changes to rear springs etc can be made which support the usual condition of the vehicle, and, allow the Front and Rear AHC pressures to be brought within the FSM-specified ranges for best damping performance for the usual condition of the vehicle.
Vehicle Operating Height -- also called ride height -- and AHC Pressures:
More height means increased AHC pressures (and vice versa) and that would have to be compensated later.
Few people use the very finnicky, hard-to-measure FSM height specifications. Instead the approximations of hub-to-fender tape-measurements of 19.75 inches (or 500millimetres) at Front both sides, and, 20.50 inches (or 520 millimetres) at the Rear both sides, have been found to be good enough for most purposes for a stock vehicle. This approximation assumes no chassis or body damage nor unusual wear-and-tear of suspension components, control arms, axles, ball-joints etc.
However, these nominated heights are not essential -- it is up to the Owner to decide on the chosen operating heights (or ride heights) of his/her vehicle,
within the allowable limits of the suspension geometry and drivelines.
The point is that vehicle height and AHC pressures are related.
See further comments at my Post #7 at this link:
Factory AHC Sensor Position - https://forum.ih8mud.com/threads/factory-ahc-sensor-position.1297829/#post-14730931
C1713 – Rear Height Control Sensor Circuit (there is only one Rear Sensor):
DTC-related to a Height Control Sensor circuit (C1711, C1712, C1713) indicates a definite problem in this
circuit. It might be a circuit/harness problem or a problem with the Sensor itself. The Sensor might respond to dismantling, cleaning and testing, but frankly an original Sensor on this 2002 vehicle is now 20 years old -- it may be best to cut to the chase and replace the Sensor with a new Toyota/Lexus or AISIN part.
Toyota/Lexus Height Control Sensors – Part Numbers:
89405-60012 (Front Right)
89406-60022 (Front Left)
89407-60010 (Rear)
Or consider AISIN Sensors -- because AISIN are suppliers to Toyota/Lexus:
Aisin Height Control Sensors – Part Numbers:
HST-020 (Front Right)
HST-021 (Front Left)
HST-026 (Rear)
If replacing, for reliability suggest avoid the unhappiness with Height Control Sensors which seems to arrive with cheap short-life substitutes, fakes and second-hand items. It is easy to find cheap substitutes on the web but IH8MUD stories about these mostly are unhappy ones.
In such a situation, the ECU may place the AHC/TEMS system into the defined ‘fail safe function’ if the Suspension Electronic Control Unit (ECU) cannot resolve differences in signals coming from the three Height Control Sensors. See “C1713” in the FSM Diagnostics section. Then AHC operation is prohibited. Adaptive damping by TEMS is prohibited. The Front and Rear of the vehicle may arrive at different heights. The Owner is left puzzling about what has happened.
The point of this long part of the story is that the benefits of a healthy AHC and TEMS systems are lost easily if Height Control Sensors are forgotten and not maintained and replaced when necessary. Such requirements are no different to, say, brake or steering components or the components of any other major system on the vehicle.
Some more observations about Height Control Sensors are found in my post #7 at this link:
Factory AHC Sensor Position - https://forum.ih8mud.com/threads/factory-ahc-sensor-position.1297829/#post-14730931
Now the possible bad news – the Sensor readings on Techstream give no reason to suspect problems with the Front Height Control Sensors, so leave them for now.
However ….
Beware -- absence of DTC's C1711, C1712, C1713
does not provide assurance that a Sensor circuit is healthy! It simply means that the signal is within the FSM-specified range (0.3 volts to 4.7 volts) but
does not indicate whether the actual signal is correct for the set height position. See link in previous post #4 this thread to “Diagnostics” section of the FSM.
A fault with brushes or the carbon track or effects of moisture ingress, corrosion or whatever may still allow an acceptable voltage signal from the Sensor within the the required range (so no DTC) but cause an incorrect signal for the height of the vehicle and result in aberrant effects.
There are multiple stories on IH8MUD about AHC difficulties and strange vehicle behaviour which come down to faulty Height Control Sensor(s) even though no DTC is given. These Sensors are simple, robust, longlife items -- but they are 'wear items'. Original Sensors have been operating in the tough underbody environment for at least 15 years (2007 vehicles) or maybe up to 24 years (1998 vehicles) and eventually need replacement.
C1736 – Height Control Accumulator Solenoid Circuit:
Faults on the Height Control Accumulator and its solenoid valve are uncommon but be aware of attached Technical Service Bulletin (TSB) CP-3006.
Related wiring harness problems have surfaced in recent times and these are discussed at Post #9 at the link below and in other related posts by
@suprarx7nut,
@2001LC and others:
AHC done? - https://forum.ih8mud.com/threads/ahc-done.1299423/#post-14719487
There was another real world example today provided by
@84bj60 at Post #4:
* Urgent * AHC Front leveling control valve testing - https://forum.ih8mud.com/threads/urgent-ahc-front-leveling-control-valve-testing.1300477/#post-14731576
It is a reminder that all DTC’s showing up on Techstream relate to the
circuit and not only a particular device itself.
C1764 – Height Control Accumulator Solenoid Circuit / Pressure Sensor Circuit / Fluid Clog:
As above for C1736 – these may be related circuit problems.
However, as these vehicles age, it also is not surprising that there are an increasing number of experiences with original AHC Pumps which, over time (many years), have developed partial blockages in the internal strainers within the AHC Pump.
Another too-long post with many pictures near the end of Post #16 and observations concerning the AHC Pump -- including related contributions from
@Moridinbg,
@suprarx7nut and
@2001LC and others -- can be found at this link:
Food for the "AHC is unreliable and it can get you stranded in the middle of nowhere" crowd, I guess. I am in the middle of nowhere in Argentina and I am getting C1762 after trying to rise the vehicle to H. It almost got to the expected height, then aborted and dropped to N. After clearing the...
forum.ih8mud.com
Rear Coil Springs for additional weight, reduction of Rear AHC load and pressures:
LHD vehicles with AHC have a longer LHS rear coil spring whereas RHD vehicles with AHC have the same length on both sides. Apparently the reason for the longer LHS rear coil spring in LHD vehicles is to provide a little more preload to compensate for driver and fuel being weighted more to the left hand side in LHD vehicles.
Many IH8MUD members with AHC on LHD vehicles and with AHC on RHD vehicles replace/upgrade their OEM rear coil springs with the stronger KING KTRS-79 springs (higher spring rate: OEM are about 95 pounds per inch of deflection whereas KING KTRS-79 are about 130 pounds per inch of deflection).
The KING KTRS-79 coils springs are manufactured in Australia -- sometimes bought direct from the manufacturer or from various distributors and eBay sellers in other countries
These springs are packaged in pairs with both springs of equal length.
Some LHD owners add a small spacer (10mm?) on the LHS when installing KING KTRS-79 rear coil springs.
An alternative to upgraded springs would be to install airbags in the existing coils which can provide assistance when occasional heavy loads are carried or towed. However, if the loads are constant, the existing OEM springs are lightweight and would be 20 years old in your 2002 vehicle, and so upgraded rear coil springs may be the best bet.
Anyway, all of the above must be enough to think about for one day under the shade tree!!
