AHC Height Offset Utility How-To (2 Viewers)
- Thread starter radman
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There's a full AHC suspension manual that @TeCKis300 has sent me linked here. Full diagrams of fluid flow throughout the vehicle, logic, and breakdown of how fluid and the checks work internally on the pump.
I feel like the culprit of the driver corner lean is the front accumulators getting fluid from a valve on the passenger side, I think in between the F/R passenger side accumulators. The system should compensate for the line runs being of different length, but maybe over time it becomes more noticeable? Although once you see it on your truck, I feel like I've been noticing it on the road more.
Bring this up because I'll be using the HOU soon to raise my front driver corner .5" to address this.
I feel like the culprit of the driver corner lean is the front accumulators getting fluid from a valve on the passenger side, I think in between the F/R passenger side accumulators. The system should compensate for the line runs being of different length, but maybe over time it becomes more noticeable? Although once you see it on your truck, I feel like I've been noticing it on the road more.
Bring this up because I'll be using the HOU soon to raise my front driver corner .5" to address this.
From what I can tell from the system schematics, it's possible AHC has some authority to level side to side. There are gate valves that give it this control in the hydraulics Though if they open as the manual describes when driving, the side to side pressures will equalize. It may be that the system re-balances again when at a stop if beyond some margin, but I can't say I've ever felt side to side leveling, like the system does for front to back.
Another case where it would be cool to know what the ECU does during different driving conditions. The 100 series manual offers a little more insight, although, since they are different systems, who knows if they behave the same. The 100 Series doesn't appear to have the center suspension control cylinder that allows the corners of the system to work against each other during different scenarios. For 100 series it says gate valve open for normal driving and closed when cornering. The 200 series just says "normally closed" and throws in the infamous "opens in accordance with signals form the suspension control ECU."
(100 Series Description of Gate Valves)
Nice. I was looking for that detail in the 200-series manual and it doesn't suggest that it's used in that manner. It makes sense that it could be used to increase/decrease sway resistance, but the 200-series AHC system has other primary faculties to do that. Still doesn't mean it won't use the gate valves in that way, perhaps in full off-road use to allow more compliance. We don't have that level of programming detail, but the manual describes the primary controls for roll posture to be center control valve, damping, and spring rates.
Getting back to the lean issue, just checked mine and it measures with 3/8" delta side to side, with the driver lower. I have done the height offset to increase the neutral height. Don't recall doing anything particularly special to level her side to side between the physical or height offset utility. But I seem to recall the front physical sensors did have some influence as I was adjusting?
Can anyone else confirm that they were able to produce different side to side results?
when we go snow wheeling, there are circumstances where wheel speed is a good thing even though we aren’t actually moving that fast, and maintaining the high mode would be nice for that. This upcoming winter will be my first deep snow trips in the LX, so I’ll see how often this comes up.
I’ve had the front left corner only raise. So it can control at least the front corners separately
My theoretical thoughts on this are that no matter how you set the height control sensors, at least per axle) because of the gate valves, if they ever open the truck will end up having even pressure on both sides of an axle, so raising one higher than the other to try to compensate for lean will be short lived, but then possibly come back the next time the truck adjust height. No matter what, every time the gate valve opens, the axle will reset. So if vehicle weight or more or less tired springs causes an imbalance, the imbalance will remain.
I’m talking about when sitting at a light, I’ve had low corners go up, or high corners go down.
I messed about with the height utility one day for a couple hours, results were inconclusive
Right, I definitely agree the system can move one corner at a time. I'm just saying that once it opens the cross axle gate valve, which I assume it does semi regularly, then any differences in height will be based on the weight/springs of the truck rather than pressure in the AHC system, because the pressure will be the same at both corners of an axle, and I don't see anyway around that, unless the truck readjusts height often after opening the gate valve. Which i suppose is possible. I assume it would do this if it used the gate valve and one side dropped outside of whatever the AHC ECU thinks is an acceptable range and then tried to lift that corner. I suspect it just depends on how often it makes those adjustments.
@lx200inAR I agree with everything you are saying, logically it all makes sense.
What im trying to understand however is how the system regulates pressure. If it has no hydraulic sensor for PSI or mPa anywhere in line, then somewhere in that valve box / controller it is either reading it or it is just mechanically limited. How else would the truck deny the lift if overloaded without actual failing at the pump or blowing a line or whatever else?
Also, @grinchy thats exactly the behavior i encountered in my first foray into the HOU. I could get any independent adjustment i wanted within the boundaries but it would choose when to do it randomly, or sometime not at all. I also found that it had to be a combination of raising one side AND lowering another for it to really stick. But like you said intermittent at best. Its making its own decisions and im more and more confident everyday that its the springs in the rear.
What im trying to understand however is how the system regulates pressure. If it has no hydraulic sensor for PSI or mPa anywhere in line, then somewhere in that valve box / controller it is either reading it or it is just mechanically limited. How else would the truck deny the lift if overloaded without actual failing at the pump or blowing a line or whatever else?
Also, @grinchy thats exactly the behavior i encountered in my first foray into the HOU. I could get any independent adjustment i wanted within the boundaries but it would choose when to do it randomly, or sometime not at all. I also found that it had to be a combination of raising one side AND lowering another for it to really stick. But like you said intermittent at best. Its making its own decisions and im more and more confident everyday that its the springs in the rear.
I think the ECU opens the leveling valves and triggers the pump to add pressure to the system increasingly, then reads the height sensors. Once the truck reaches the correct height the ecu closes the leveling valves. I think the pressure sensor is mostly there for fault management.
My best guess for the attempts at leveling an overweight vehicle and failing but still working best it can is that the pump pressurized as much as it can, which will be too little to completely raise the truck. I have never done this so I dont know what it actually looks like as far as how long the pump runs for (full 135 sec?) or if the truck decides it just can’t make it and gives up in a shorter amount of time. Also don’t know if it triggers any AHC lights in the dash when it can’t make it.
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When overweight, mine wont even flash the Up arrow like it does when it's raising. It's a if the ECU decides its a no-go and disables the AHC knob. unloading the rig while running doesn't re-enable AHC - I had to restart the rig.
Also, I once made the mistake of loading my basket in Lo mode, and it couldnt raise up. I had to initiate the lift and then run out and assist by lifting the basket.
18” hitch extension: 20lbs
Basket: 55lbs
100-150lbs of load
the kicker is that it’s not 200lbs of tongue weight. The extension makes that 200lbs act as a cantilever on the rear axle. Anyone know how to calculate the mass/weight when 200lbs is pushed out 18”?
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This is about what I expected happens. Either a max run of 135 seconds on the pump or some pressure triggers an internal DTC that disables the system until a restart reenables it. I assume that max pressure on a functioning system that is trying too lift too much weight is lower than the trigger pressure of the DTC that exists to detect faulty valve solenoids or clogged lines.
As to the cantilever question. I’ve only dabbled in that form off engineering, but if you simplify a lot of the equation, it’s a pretty strait forward distance times weight formula. If you thought of the truck as a teeter totter with the rear axle as the fulcrum. Adding 200lbs at about 5-6 ft from the rear axle means you are doing about 1-1.2k ft-lbs of work at the axle. This means you are unloading the front axle by some amount. I have no idea what that implies to the actual weight on the axle. But if I’m not mistaken, adding leveraged weight doesn’t change the weight added to the truck, it just moves the weight from one axle to another.
You could do the science for us and have truck axles weighed with that stuff centered between axles and then mounted in the way way back.
also side question, can you pop a wheelie loaded like that? If not, time for more gears.
Im also thinking its a simple time-out circuit if there is no pressure sensor on any of the diagrams. Thats what is most likely to happen.
Adding to the bizarre behavior motif @radman, if im not level front to rear in my driveway (its very sloped) when washing the ride, it will raise and not show H until a restart.
Ive never had it fail to lift, but ive had it refuse many times for things other than brake hold duration. (which also doesn't make sense because it will happily lift the front anytime under 65 at a highway stop light with brakes constantly applied, AND it will do it every-time with the parking brake on. There is no shortage of odd behavior with AHC. We are getting close to figuring out all of its logic though. I do wish we could just find the engineering team behind the 200 suspension.
Height Offset can adjust a maximum of .8", so you move the physical sensors first, and then you have .8 to play with.
Step 1: Find Level Ground. I'm not sure how picky the rig is, so I'm within 1/4" on all 4 corners using various thicknesses of wood.
- 1mm of movement on the sensor equates to 2mm on the rig.
- In theory, assuming there’s enough stoke in the shocks, you might be able to add .8” on top of the “sensor lift” method (move the screws to the bottom (front) and top (rear)).
View attachment 2244877
View attachment 2244878
Step 2: Prepare suspension. Check tire pressures, put transmission in neutral, Cycle height from LO to N 2 times, and bounce corners to “stabilize suspension”. All doors have to be closed for this, and I keep my driver window down to access the ahc controls (And laptop).
Step 3: enter Techstream, AHC, Live Data, and take a picture of your values before you mess with anything.
Height Offset Utility only changes the 4 highlighted values below:
View attachment 2245033
With these numbers, my driver Front was 1/2" low.
View attachment 2245034
Step 4: Start HOU. Select FL, enter measured value of "4.5", enter standard value of "4.0"
This will add .5 to your FL height adjust
FL height adjust went from -0.3 to 0.2. After this, I added another .5" adjust to get to 0.7 (and added the same to FR)
The maximum height adjust is 0.8.
Step 5: cycle through heights and measure again.
Step 6: slap on some 35"!!!
Doing mine hopefully Tomorrow.
Hi @radman is the value Step 4: Start HOU. Select FL, enter measured value of "4.5", enter standard value of "4.0" standard or would it vary?Height Offset can adjust a maximum of .8", so you move the physical sensors first, and then you have .8 to play with.
Step 1: Find Level Ground. I'm not sure how picky the rig is, so I'm within 1/4" on all 4 corners using various thicknesses of wood.
- 1mm of movement on the sensor equates to 2mm on the rig.
- In theory, assuming there’s enough stoke in the shocks, you might be able to add .8” on top of the “sensor lift” method (move the screws to the bottom (front) and top (rear)).
View attachment 2244877
View attachment 2244878
Step 2: Prepare suspension. Check tire pressures, put transmission in neutral, Cycle height from LO to N 2 times, and bounce corners to “stabilize suspension”. All doors have to be closed for this, and I keep my driver window down to access the ahc controls (And laptop).
Step 3: enter Techstream, AHC, Live Data, and take a picture of your values before you mess with anything.
Height Offset Utility only changes the 4 highlighted values below:
View attachment 2245033
With these numbers, my driver Front was 1/2" low.
View attachment 2245034
Step 4: Start HOU. Select FL, enter measured value of "4.5", enter standard value of "4.0"
This will add .5 to your FL height adjust
FL height adjust went from -0.3 to 0.2. After this, I added another .5" adjust to get to 0.7 (and added the same to FR)
The maximum height adjust is 0.8.
Step 5: cycle through heights and measure again.
Step 6: slap on some 35"!!!
AHC Questions:
What initiates an automatic adjustment?
¼”, ½”, 1”, 2” slope?
Is automatic leveling only a front to back function or side to side as well?
I feel my front drop/raise all the time. Can the rig make this same kind of adjustment left to right? i.e. passenger side raises/lowers to meet the driver’s side?
Is the front primary? Meaning, the front always moves in order to compensate or can the rear adjust as well?
Does self-leveling occur at highway speeds?
Rig drops into “Fast Lo” Mode at 62mph. will the rig ever attempt to self-level during these speeds?
Does weight affect height? i.e. Does a full tank of gas affect rear passenger height?
This thread tells me no:
LX570 Lean/Sag
Does your mechanic know how to properly prepare AHC for alignment? In theory, if rig is on an incline and has attempted to self-level, could this affect alignment readings? Ideally, the alignment table is level, tech drives on it, raises the table, make sure you leave doors closed to allow rig to self-level, turn off AHC, then turn off car. Or none of this really matters for Alignment?
I’ve seen people mention measuring from wheel center to fender. Unless you cross-hatch the center cap, there’s potentially a bit of error here, right? I’ve been measuring top of center cap to fender or top of rim to fender.
Other helpful links I’ve come across, for reference.
Lift it:
LX570 AHC height modifications (lift it!)
Bleed it:
LX570 AHC “Basics”
AHC history:
AHC History and possibilities
I would like to do it to mine and I have these measurements currently. N on neutral ground
