Ok, just starting to get my feet wet here. Let’s throw out the previous height measurements, I’m measuring more accurately, consistently, and from L to N (instead of H to N as I was previously). Here’s where I started today:
LF RF
490 489
LR RR
515 524
Techstream neutral data, coming up from low.
View attachment 2561920
To summarize a few hours of “work”, I gave the torsions a few turns to get the pressures down, moved the height sensors up to the center on the slots (they were at the bottom) and this is where I’m sitting now.
View attachment 2561888
My front end height is up to 502mm (factory perfect!) on each side, rear is roughly unchanged. Tomorrow I hope to fine tune the sensors to get them to zero. The rear coils currently have 15mm of spacers (10+5), I have some 30mm spacers to swap in and get the pressure down a small amount back there. I may stack one of the 5's or 10's on to level it out.
Since I posted the video on Sunday the weird noise happened once on Monday (or was it Tuesday?) morning and then it surprised me again this morning. Never heard it once during all of my work today.
Hi
@GTV
By now you must be thinking that the AHC/TEMS system needs a lot of ‘love’ – and compared to a set-and-forget conventional suspension, this is certainly true. It is always fair to wonder and judge whether the benefits are sufficiently worthwhile and fit-for-purpose. That is always a personal decision. It suits my purposes and so I am ‘keeper’ – but I acknowledge that this choice involved a lot of study – but once done, it is not hard to stay on top of it.
Anyway, here are my further comments – lengthy as usual, but don’t worry, the well is now pretty close to dry!
Starting point is always front ‘cross level’ as the vital first step – and this looks good on your numbers -- worth checking again after any torsion bar adjustments and after suspension has settled after an around-the-block drive. (Note that Height Control Sensor adjusters cannot and should not be used for front cross-levelling).
Then heights – your hub-to-fender tape measurements at “N” look good -- near enough to IH8MUD recommendations. (By the way, the Factory Service Manual prescribes a different, very fiddly but technically correct method of measuring heights. The IH8MUD hub-to-fender approximations are not factory-approved but are good enough for most purposes).
Then AHC neutral pressures – your Front pressure looks good, Rear pressure looks good although at the high end of the range as you mention. Some correction with spacers seems worthwhile to give a some load flexibility while keeping pressures in range. Given their age, rear spring replacement is in the cards at some point. If the goal is vehicle in near-stock condition, then best to stay with new OEM AHC springs, spacers if desired/needed, plus airbags if more load flexibility is required. For additional load, heavy accessories etc, next step up is KING KTRS-79 replacement springs (spring rate 130 pounds per inch of deflection compared to 95 pounds per inch for new OEM AHC springs). I have KTRS-79, as expected they certainly give a firmer ride, not unacceptable, when the vehicle is empty, but give an excellent ride and good adaptive damping when the vehicle is loaded for touring.
Previously, 12 graduations were reported at AHC Tank between “HI” and “LO”, so it seems reasonable to assume your ‘globes’ are in good condition.
Height Control Accumulator pressure is showing zero in both screenshots rather than around 10.5 Mpa which is more usual. The zero Accumulator pressure is surprising given the previous Youtube indication that the raise-from-“LO”-to-“N”-cycle took 16 seconds – which is reasonably normal – and the AHC Pump running for another 15 seconds (or more) to re-charge the Accumulator also would be normal. Maybe this means that the readings were too quick, taken before the AHC Pump had stopped and before the Accumulator had re-charged??? Otherwise, this may indicate some problem with the solenoid valve at the front end of the Accumulator – which is a possible cause of the strange end-of-cycle noise. If there are suspicions about this, then observing this valve open and close by touch/sound during a raise, or, by watching “SLAC” turn “ON” and “OFF” on Techstream during a raise, may give an indication (see my previous post).
The point is that if a fault arises in this circuit, the ECU prohibits the control of accumulating and releasing of the pressure of the height control accumulator and may cause strange sounds. Actual timings of valve and pump operation are a useful indicator.
Your Height Control Sensor readings are close to zero and within the FSM-suggested tolerance of +/- 5 millimetres. Maybe they can be tweaked a bit for fine-tuning but the differences are not large enough to warrant much, if any, attention. Note that adjusting the positions of the Height Control Sensor adjusters in pursuit of the perfect zero will be accompanied by height changes of the vehicle – a small movement of the adjusters results in a significant movement in height. In a healthy fault-free system operating within its load limits, the ECU always will cause the AHC to self-adjust to the “null point” (meaning close to zero, within tolerance) as determined by the Height Control Sensors – that is the purpose of Active Height Control.
Fluid Temperature shows as -22degF which suggests that Temperature Sensor was disconnected for testing – if so, seems normal.
Steering angle appears large in both screenshots – seems unusual but maybe this just reflect the steering position at the time of testing??? Otherwise, the steering angle input (from the sensor in the steering wheel) will affect the performance of the Gate Valves (in the Control Valve Assembly) which allow or disallow connection between Right and Left sides of the vehicle at road speeds. The Gate Valves are normally open when the vehicle is stationary, so the Steering Angle should not affect pressure tests etc.
What’s next???
The only significant adverse ‘vital signs’ coming from the AHC/TEMS system appear to be
- reported harsher than expected ride, and,
- zero Height Control Accumulator pressure reading, and,
- sometimes noisy end of “LO” to “N” raise cycle,
- three DTC's picked up and noted by Techstream.
These ‘signs’ may be related.
Reported harsher than expected ride:
Suggest check for ‘fail safe conditions’ which lock AHC/TEMS into Damping Step 8 or Sport Mode 2 and disallow adaptive damping or prevent valve operation, as mentioned in my previous post. Way back at Post #45 at Page 3 of this thread I attached the AHC Diagnostic section of the Factory Service Manual. This is a boring read – but it is worth looking through those pages to see how the Diagnostic Process is meant to work and to identify various ‘fail safe conditions’ which can arise and the associated symptoms which can and do help to diagnose problems.
To summarise, a ‘fail safe condition’ in which some or all of the AHC/TEMS functions may be prohibited by the Electronic Control Unit may arise from various faults including those in the following list. As explained in the FSM, a Diagnostic Trouble Code (DTC) may (or may not) be shown when these faults occur. Absence of a DTC does not mean that there is no fault. It is better to use the Problem Symptom Table as a starting point.
C1711 Height Control Sensor Circuit – you have experienced this previously,
C1718 Pressure Sensor Circuit – seems unlikely, AHC neutral pressure readings were obtained,
C1721 and C1723 Damping Force Control Actuator Circuits – seems less likely without related symptoms,
C1731 to C1736 Control Valve Solenoid and Accumulator Solenoid Circuit – possible!
C1751 AHC Pump and Motor Circuit – seems unlikely, motor and pump are operational,
C1762 to C1764 Fluid Pressure Abnormality Circuit – possible!
NB: If the DTC C1764 is detected, the ECU prohibits the control of accumulating and releasing of the pressure of the height control accumulator
C1781 Steering Angle Sensor Circuit – possible, consider later.
Can you identify the three (3) Diagnostic Trouble Codes (DTC's) picked up by Techstream and indicated on both screenshots? Should be revealed by hitting the blue Trouble Codes button.
It is also suggested that some obvious but sometimes overlooked effects are reviewed. For example, the AHC/TEMS system is designed to run on Toyota settings and assumptions. This includes OEM wheels and “P” rated Passenger tyres running at 32 psi !!! Very few of us follow this prescription. In my case I run BFG 275/65R17 KO2 Light Truck “E” rated tyres on OEM wheels at 40psi on sealed roads – and there is a ride quality penalty for my choice.
Sometimes noisy end of “LO” to “N” raise cycle:
If this were my vehicle, I would proceed as follows – you may wish to consider some or all of these steps or see what others may have to say -- there is plenty of wisdom in IH8MUD:
- Carefully re-bleed the whole AHC system several more times until very sure that air has been purged – ‘several times’ as part of the effort to eliminate as much fluid as possible containing dissolved air as well as entrained air,
- Given that the system will be opened for re-bleeding, take the opportunity to pull the AHC pump, dismantle and clean it, as well as clean the internal strainers by backwashing. As shown at the links in previous posts, this is not a difficult job. It is also a good way of getting a ‘feel’ for how much debris and jelly-like ‘gloop’ may be in the system, impairing fluid flow as well as impairing valve operation and pump operation,
- Similarly, take the opportunity to open the AHC line at the Attenuator and release any entrapped air – not really sure that this will make a difference but it cannot do any harm,
- Test and resolve any faults which may be forcing the system into a ‘fail safe mode’ as listed above and also resolve the three Diagnostic Trouble Codes (DTC's) picked up by Techstream,
- Re-assemble and re-pressurise the system – if necessary use the “active test” procedure to re-start the AHC Pump with a AHC Fluid in the tank.
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How do you change the readings from freedom units to metric?
. I have an '03 LC that came with JBL speakers. The sub says 7.4ohm 25 W. Considering upgrading the sub while I have everything removed from the rear. Was that the spec on your LC?
