Clockwise = tightening the nut = righty tighty when you’re staring up at it from under the truck. Doesn’t matter which way your head or feet are as long as you’re looking up from underneath.
AHC Basics for dummies Video re CrossLeveling, Height Sensor adjustment, TB tweaking (1 Viewer)
- Thread starter Madadder
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Yes – when looking from below at the bolt-head on the Torsion Bar adjuster, turn clockwise for two separate purposes:
- increase level on that side during the ‘cross-levelling’ step. NOTE: The main purpose of the so-called ‘cross-levelling’ step on an AHC vehicle is to ensure that both torsion bars are carrying equal loads. This will happen when the hub-to-fender distance is the same on Front Left and Front Right,
- increase the load carried by BOTH torsion bars. This reduces the load carried by the front AHC system. In this way, the front AHC neutral pressure is lowered. NOTE: For comparison with FSM specifications, neutral pressures must be measured with vehicle at the correct operating heights.
These are the only purposes of the torsion bar adjusters on an AHC vehicle.
The ‘operating height’ sometimes called the ‘ride height’ – hub-to-fender: front 19.75 inches, rear 20.50 inches – on an AHC vehicle is set by moving the Height Control Sensor adjusters and not the torsion bar adjusters. This is because the AHC system uses the average of the two front Height Control Sensors to choose the Front Height of the vehicle and uses the single Rear Height Control Sensor to choose the Rear Height of the vehicle, regardless of what the front torsion bars and rear springs may be doing (within limits).
Different to a non-AHC vehicle, on an AHC vehicle the Torsion Bar adjusters are NOT used to set the ‘operating height’.
At the front, shortening the Height Control Sensor adjuster using the double-ended Heim bolt (or pushing the slider upwards) causes the vehicle to rise. Start with small changes at the Height Control Sensor adjusters – say 2 or 3 millimetres or one-eighth inch to see the effect of maybe 10 to 12 millimetres or half-inch on the hub-to-fender measurement.
The Electronic Control Unit (ECU) for the AHC system assumes that the torsion bars are correctly and equally set -- but the ECU has no connection to the torsion bars and no way of knowing whether they are correctly set or not. If the torsion bars are not equally loaded, then the vehicle will perform strangely on the road – Left turns will feel different to Right turns – and it will be more difficult to set the ‘operating heights’ correctly.
Then, if incorrect or widely differing ‘operating heights’ cause a conflict to be received by the ECU, it will default to a ‘fail safe’ mode in which variable damping will cease and poor ride quality will be experienced.
For all of that, the AHC system is not as complicated as it may seem at the start, there is nothing to fear, nothing which cannot be corrected -- you have done the research – all will become clearer as you learn-by-doing.
There is an important safety rule: Measurement of ‘operating heights’ and ‘neutral pressures’ etc must be done with the engine and AHC “ON”. Turn engine and AHC “OFF” when making actual adjustments to avoid risks of sudden movements of the vehicle and potential injury risks to head, hands and body. Then turn engine and AHC back “ON” to see the effects of changes with head, hands and body well clear of the vehicle.
Torsion Bar Adjuster
Left and Right Front Height Control Sensor Adjusters
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- Thread starter
- #23
You sir are my hero! I can do this! Thanks!!!
Thank you for the very helpful info and pics!
In my case, 18.5" driver side hub-to-fender and 19.25" passenger side, would it be sufficient to crank up the driver side torsion bar, or do I also likely need to adjust the height sensors to make both sides at 19.75"?
Thanks!
Do not adjust height sensors in your case. Crank torsion bars to get the side to side level, then pull up techstream and see if the +/- values on there match up with reality. If they do, you're done. If they do not (IE you're level, but techstream says on side is .75 inch low) then you would adjust height sensors.
Keep in mind the height sensors do not control side to side height at all. The ONLY thing that determines side to side height is the torsion bars.
Helpful video and timely, THX @suprarx7nut
I forgotten about disconnecting temp sensor. After seeing your video, I' rooted around today in mud 100 section. I found only mention, not a recommendation. With respect to disconnecting height sensor.
Anyway:
I happen to be setting up and 03LX. Thay I just put new OEM LC AHC coils and 30MM spacer on. I could see that at some point, someone had made changes to height adjusters position from factory preset lowering the vehicle.
In Tech stream I was getting high pressure reads, which was concerning. As vehicle height was set low, which puts more load on T-bars and coils:
Front both 19 5/16" And rears both side 19 11/16" Pressure Frt 7.9MPa and Rear 6.7MPa. After coil & spacer installed.
My goal was to get pressure down to help out the old weak globes ~8 grade w/233K on the clock. @PADDO clued me to the benefit of new coils w/spacer some years ago.
Anyway, after tweaking the height adjusters sensors and actual lower the rig more, to reduce pressures. My pressure where still high. I watch your video an a light went off
I'd not been disconnecting the temp sensor. Started searching mud and could tell by looking at screen shots (not one I saw) was disconnecting temp sensor based on their temp reading.
So thought well let's see what happens. BAM
. Rear drop from 6.2MPa (I now had both frt & rear heights even lower). To a respectful 5.6MPa with rear at only 19 1/2".
I then readjusted all 3 sensors and T-bars.
Now Fronts 19 7/16" at 6.8MPA and Rears 20 3/16" at 5.9MPa. and 9 Grads now. I'm still a little low in height, but not bad pressure for old tired globes. Should add a few years to them!
Need to test drive and see how if feels.
In searching mud, every screen shot I looked at, had normal looking temp and high rear MPa readings. Seems where adjusting T-bar no big deal to leave temp sensor connected. But if adjust height sensor. Especially rear height adjuster. It make a huge difference.
Notice temp -22 F in shot below.
I forgotten about disconnecting temp sensor. After seeing your video, I' rooted around today in mud 100 section. I found only mention, not a recommendation. With respect to disconnecting height sensor.
Anyway:
I happen to be setting up and 03LX. Thay I just put new OEM LC AHC coils and 30MM spacer on. I could see that at some point, someone had made changes to height adjusters position from factory preset lowering the vehicle.
In Tech stream I was getting high pressure reads, which was concerning. As vehicle height was set low, which puts more load on T-bars and coils:
Front both 19 5/16" And rears both side 19 11/16" Pressure Frt 7.9MPa and Rear 6.7MPa. After coil & spacer installed.
My goal was to get pressure down to help out the old weak globes ~8 grade w/233K on the clock. @PADDO clued me to the benefit of new coils w/spacer some years ago.
Anyway, after tweaking the height adjusters sensors and actual lower the rig more, to reduce pressures. My pressure where still high. I watch your video an a light went off
I'd not been disconnecting the temp sensor. Started searching mud and could tell by looking at screen shots (not one I saw) was disconnecting temp sensor based on their temp reading.
So thought well let's see what happens. BAM
. Rear drop from 6.2MPa (I now had both frt & rear heights even lower). To a respectful 5.6MPa with rear at only 19 1/2".I then readjusted all 3 sensors and T-bars.
Now Fronts 19 7/16" at 6.8MPA and Rears 20 3/16" at 5.9MPa. and 9 Grads now. I'm still a little low in height, but not bad pressure for old tired globes. Should add a few years to them!
Need to test drive and see how if feels.
In searching mud, every screen shot I looked at, had normal looking temp and high rear MPa readings. Seems where adjusting T-bar no big deal to leave temp sensor connected. But if adjust height sensor. Especially rear height adjuster. It make a huge difference.
Notice temp -22 F in shot below.
Great video. Thank you for creating that. It was well laid out and covered everything you always wanted to know about AHC, but were afraid to ask. Compliments.
I did see you struggle with the USB connection. I'm wondering if your XHorse M-VCI was set to the virtual machine. If not, the VM will not see this device. You can make any USB device available to the VM with the pull-down menu Devices -> USB -> XHorse M-VCI.
Thanks a lot for the helpful clarification! I'll give it a try.
DanInDenver
GOLD Star
@suprarx7nut great video, have done this in the past and it’s great to have it all together in a video.
Question: With steel bumpers and sliders does it make sense to change out TB bars to at least LC Non AHC size?
I have LC non AHC springs.
Starting to get bouncy and thinking of new globes as well.
Question: With steel bumpers and sliders does it make sense to change out TB bars to at least LC Non AHC size?
I have LC non AHC springs.
Starting to get bouncy and thinking of new globes as well.
Well, it's all about the weight. I have aluminum front with steel bull bar and a 12.5k winch and sliders. If you have a steel bumper with no bull bar and no winch, you probably have less weight than I do. Mine feels quite good and I've got the torsion bars supplying too much of the support force right now. I probably need to wind them back a few turns.
Consider this. From what I've read in various sources, the AHC system is meant to carry somewhere between 40 and 60% of the vehicles weight. The vehicle has around 2500 lbs (wild guess) over each axle. If you increase the weight by 200 lbs in the front, that's an increase of only ~8% on the front axle.
AHC vs non AHC springs are, theoretically, different by roughly 40%+. If you add 8% weight and change spring rate by 40% you're adjusting way too far. You go from being 8% off to being 32% off in the other direction.
I'm a fan of keeping the LX AHC bars in almost all cases. I'm not sure you can add enough weight to make the non-AHC bars have a more appropriate spring rate and the AHC bars have plenty of adjustment to carry a LOT of extra weight.
To @suprarx7nut:
Compliments on your exceptionally good AHC video and your clear replies to issues – thank you – I have found all of these very helpful.
To @DanInDenver:
In support of the advice from @suprarx7nut, the FSM offers the following guideline:
Source: https://lc100e.github.io/manual/ then follow tabs starting at the top:
New Car Features > CHASSIS > Suspension > Active Height Control Suspension
(this reference provides a good general description of all features of the AHC and TEMS systems)
My vehicle is fine on original stock Torsion Bars with a full steel ARB Deluxe Bar plus KAYMAR Rear Wheel Holder, plus towbar, no sliders, plus the additional weight of the 1HD-FTE turbodiesel engine plus passengers and all requirements when touring. I replaced all four 'globes' at 8 graduations -- very conservative but I wanted reliability not problems on several trips across Australia. I did have to be careful to adjust evenly when cross levelling with Torsion Bar adjusters (low side up, high side down, both equally per FSM) so as to leave plenty of thread available on the Torsion Bar adjusters for subsequent adjustment of front AHC neutral pressure into the lower part of the specified range. Final trimming for correct front hub-to-fender ‘operating height’ was done with front Height Control Sensor adjusters, then front and rear neutral pressures were checked with heights correct. Finally “LO” to “HI”graduations were checked at the AHC tank with neutral pressures correct. All good – after I learned how to do all these things properly in the right sequence on IH8MUD!! Incidentally, then I added KING KTRS-79 springs plus Firestone airbags at rear -- still good but AHC rear neutral pressure is a bit low with these rear springs when the vehicle is empty so damping is not quite as good but both are excellent when loaded for touring. The airbags probably are overkill in my case but might be useful if/when I tow something.
I also check front and rear axle loads and Gross Vehicle Mass at a weighbridge. My 2006 Owner’s Manual specifies as below, same for AHC and non-AHC vehicles. The axle loads may be conservative in the Toyota way of doing things. These details may be different in your part of the world.
@suprarx7nut: Is there possible harm in allowing the system to operate underneath the spec pressures? Other than possibly feeling “oversprung” might there be any potential damage to the system? Over-pressure, sure—seals leak more, pump has to work harder, etc. But under-pressured seems like it wouldn’t cause premature wear...?
DanInDenver
GOLD Star
Helpful post. My front end dropped a couple times in that past couple weeks. It would correct itself on my next drive. This week it dropped and wouldn't return to N.
I was finally was able to TS yesterday as I found my lost TS cable.
Sure enough FR Height Sensor had a fault.
Removed the sensor and took it apart. One spring and contact were corroded. Fortunately I had harvested 3 sensors from the local UPick junkyard.
Swapped a back and a spring and now AHC is working and I can get readings.
CTRL C in my TS will copy any highlighted rows into a text file.
Now to PB my TB bolts and do some cranking later.
1998 LX470 2UZ-FE
10/4/2020 1:39:39 PM
[AHC Live] System
[Parameter] [Value] [Unit]
FR Height Control Sensor -0.0 inch
FL Height Control Sensor -0.1 inch
RR Height Control Sensor -0.1 inch
Front Pressure Sensor 8.3 Mpa-g
Rear Pressure Sensor 7.1 Mpa-g
Accumulator Press Sensor 10.3 Mpa-g
Oil Temperature Sensor 127 F
I was finally was able to TS yesterday as I found my lost TS cable.
Sure enough FR Height Sensor had a fault.
Removed the sensor and took it apart. One spring and contact were corroded. Fortunately I had harvested 3 sensors from the local UPick junkyard.
Swapped a back and a spring and now AHC is working and I can get readings.
CTRL C in my TS will copy any highlighted rows into a text file.
Now to PB my TB bolts and do some cranking later.
1998 LX470 2UZ-FE
10/4/2020 1:39:39 PM
[AHC Live] System
[Parameter] [Value] [Unit]
FR Height Control Sensor -0.0 inch
FL Height Control Sensor -0.1 inch
RR Height Control Sensor -0.1 inch
Front Pressure Sensor 8.3 Mpa-g
Rear Pressure Sensor 7.1 Mpa-g
Accumulator Press Sensor 10.3 Mpa-g
Oil Temperature Sensor 127 F
I think you're ok to be on the lower side. I'm not aware of significant negative consequences from being just below spec. I could see the dynamics of the system being slightly off, so I would always aim to be within the OEM specified range.
Nice work! Crank those front torsion bars and check again. I'm guessing you need 7 turns per side, but maybe start with 5 and check again. You're way off spec now, so it should feel much better (and improve long term durability) once you get it sorted out.
@suprarx7nut - thanks for the awesome video and guide. I went through it today and just adding a few notes if it helps others.
1. Initial readings. I did three, but only showing one screenshot. In between measurements I moved the car, backing it into the garage and then the final reading facing front again. They do read different so don't take just one measurement. Initial readings showed the front pressure to be high out of spec.
After adjusting the right torsion bar to level the vehicle (4 turns) The pressures look much better. The FL height control sensor is out of whack though. I had replaced it a few weeks ago because it snapped and just guessed at the location but didn't actually adjust it until seeing this.
Final result. Much better all zeroes for height and the pressures seem to be good.
I have a set of four globes that I intend to put on soon. The ride already feels much better, but I'm hoping that the globes will restore the factory quality to the ride. We'll see!
Thanks again for the guide
- The temperature sensor has a clip on the bottom side much closer to the fluid reservoir than it is to the exposed wires. This needs to be depressed and the connection will release easily. I was pushing on what I assumed to be the release but in the wrong place because I couldn't see the bottom side.
- I had to go out and buy a 30mm 6 point socket. I was having trouble finding a 6 point socket but an axle nut socket fit the bill.
- The torsion bar adjustment is much farther back than I assumed it would be. I thought it would be by the front suspension bits, but it's well back from that. Pretty easy to find though.
- PB Blaster and jacking up the front suspension made the nut very easy to turn.
1. Initial readings. I did three, but only showing one screenshot. In between measurements I moved the car, backing it into the garage and then the final reading facing front again. They do read different so don't take just one measurement. Initial readings showed the front pressure to be high out of spec.
After adjusting the right torsion bar to level the vehicle (4 turns) The pressures look much better. The FL height control sensor is out of whack though. I had replaced it a few weeks ago because it snapped and just guessed at the location but didn't actually adjust it until seeing this.
Final result. Much better all zeroes for height and the pressures seem to be good.
I have a set of four globes that I intend to put on soon. The ride already feels much better, but I'm hoping that the globes will restore the factory quality to the ride. We'll see!
Thanks again for the guide
uHu
Bridgeburner
@cowfountain , what's with the zero reading for the Accumulator Pressure? If you read the pressures after moving from Lo to N, the Accumulator should have over 10 MPa.
And you have a Trouble Code.
And you have a Trouble Code.
To recap longhand the steps for measuring pressures –
- AHC Front,
- AHC Rear,
- AHC Height Control Accumulator ….
The steps are:
1. Connect Techstream (or other scanner capable of reading the Suspension ECU),
2. Change heights “N” > “LO” > “N”,
3. On raising from “LO” to “N”, the green AHC light on the dashboard blinks,
4. On a healthy vehicle, the raise "LO" to "N" starts when the solenoid valve at the Height Control Accumulator is opened by the ECU,
5. AHC Fluid flows under stored pressure from the Height Control Accumulator to the ‘globes’ and more importantly to the ‘shock absorbers’ which then wholly (or partially) raise the vehicle (depending on vehicle condition),
6. The AHC Pump starts under the control of the ECU and if necessary completes the raise until the ECU receives the relevant voltage signal from the Height Control Sensors for the height selected at the console switch – “N” in this case,
7. As the vehicle raises, changing AHC Front pressure and AHC Rear pressure and height sensor readings may be observed on Techstream or other scanner,
8. When the raise is completed, the green AHC light on the dashboard stops blinking,
9. The AHC system is not finished -- the AHC Pump does not stop but continues to run until it has re-charged the Height Control Accumulator with AHC Fluid from the AHC Tank.
10. Theoretically, re-charge of the Height Control Accumulator takes about 15 seconds after the green light stops flashing for a new stock vehicle at stock weight in good condition -- but can be longer, maybe ~30 seconds or even 45 seconds for an older or heavier vehicle (much longer would suggest that there may be other problems),
11. When the Height Control Accumulator is recharged, the AHC Pump stops -- listen for this -- and the Height Control Accumulator pressure reading should appear,
12. Then, and only then and not before, it is time to read and record the three AHC pressure readings -- otherwise the readings will be misleading. (If the Height Control Accumulator pressure remains at zero, then there are other problems).
The “Oil Temperature Sensor” (meaning AHC Fluid temperature) reading on your Techstream images shows -22 degrees F. This is because the temperature sensor is disconnected per FSM for the test procedure. This will cause a Diagnostic Trouble Code (DTC) to be registered. It is best to check via Techstream that this IS the actual DTC -- and not some other cause.
Other than these details, all appears to be going well. Hang in there!!
PS: Suggest also be aware that Front AHC pressure and Rear AHC pressure as measured correctly with "N" height selected, will vary with the choice of 'ride height' of the vehicle at the "N" setting -- more 'ride height' = more weight and pressure on AHC system, less weight carried by torsion bars and springs -- so it is good practice to check with a tape-measure the hub-to-fender distances at "N" height any time AHC adjustments or tests are made. 'Ride height' can be changed by re-positioning the Height Control Sensor adjusters (not torsion bar adjusters on an AHC-equipped vehicle). Whatever choice of 'ride height' is made, the torsion bar adjustments and rear spring choices must then be made to maintain AHC Front and Rear pressures within the FSM-specified ranges -- for good damping performance and good ride comfort, assuming 'globes' are in good condition.
And with the 'ride heights' understood and AHC pressures corrected, then it is time to check overall condition of the four 'globes' by checking the amount of AHC Fluid displaced to the AHC Tank between "HI" and "LO" heights -- a difference of ~14 graduations at correct pressures means 'globes' are near new; a difference of 7 graduations at correct pressures indicates that it is time to replace all four 'globes' and recover damping performance and recover ride comfort.
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