AHC Diagnostics help

[agaisin]

OK - just tried out the Tactrix Openport 2.0 cable with Techstream latest version 6 etc. I believe I got good info, but don't know how to interpret/correct it all - especially when it comes to setting the sensors at neutral position and when it comes to correcting the high pressure on the rear accumulators. More info below.

I got the following neutral pressure readings:
Front pressure was 9.6 MPa (FSM calls for 6.9 MPa)
Rear pressure was 8.1 MPa (FSM calls for 5.6-6.7 MPa)

I got the following height sensor readings:
FR was -8.6mm
FL was -36.2mm
RR was -2mm

So - obviously I have some issues, but I don't understand fully how to correct. General principle from FSM is that pressure rises when adjusting bolt is loosened.

So - for the front to bring pressure I need to crank the TBs more till the pressure lowers, right? And then I'll be too high and will have to adjust the sensor heights, right?

On the topic of adjusting the sensor height, I don't understand the steps described in the FSM:
Inspect and adjust the height control sensor to the neutral
position.
(1) Read the value of height control sensor on the LEXUS
hand−held tester.
Standard value:
Actual vehicle height ± 5 mm (0.20 in.)
HINT:
(Example)
When the measurement value of the front vehicle height is 85.0
mm (3.35 in.), the actual value of height control sensor is −2.3
mm (−0.09 in.).

My measurements say -8.6mm FR and -36.2mm FL - what do I do to correct that? Is that purely a TB issue that I'm not level left to right?

Now for the rear, my pressure is 8.1MPa instead of 5.6-6.7 so how do I correct that - does that mean my springs need to be replaced?

And do I need to correct my rear sensor height since it read -2mm or is that in spec?

Thanks!
Art

 

[sonk76]

That looks like a sweet tool!

...once we figure ou what to do with the data that is. If this works well, I would be very interested in getting this to bring my AHC back to factory specs in terms of pressures.

I look forward to your experience on this front.

 

[Kenso]

For the rear pressure correction you would need either new springs or you could try spring spacers to take some of the load off the AHC components in the rear. How many miles on your LX, any mods? Kinda surprising a later model LX is already out of spec on the pressures.

On your techstream software, assuming you paid for it from the TIS site, how long is it good for, does it have a built in expiration date when your TIS service expires?

 

[agaisin]

For the rear pressure correction you would need either new springs or you could try spring spacers to take some of the load off the AHC components in the rear. How many miles on your LX, any mods? Kinda surprising a later model LX is already out of spec on the pressures.

On your techstream software, assuming you paid for it from the TIS site, how long is it good for, does it have a built in expiration date when your TIS service expires?

it's a 2005 with 94k miles - I bought it a yr ago with 70k. does it make sense that tbars and springs weakened that mich and then pressure goes up that mich by weakened springs? Is tht how it works? I've seen people say pressure would go down as tbars/springs weaken - however the fsm says pressure rises as tbars are loosened so I guess it makes sense, just wonder if this is typical after 6 years.

also wonder if it could be the accumulatirs losing nitrogen = higher than normal
pressure, and/or i the globes failed then higher than normal pressure. ill double check the gradation test but the susp has give/damping on all four corners an last i chekd i get >7 gradations so pretty sure my problem must just be weakened tbs and weakened springs...?

About techstream I got the professional 2 day subscription (cheapest option for scantool diagnostic access). It gives you a rgistration code for the software. My two days is up 11:59pm monday nigjt (purchased on saturdy) - so its a full/complete two days not just 24 hours from start of subscription. I am prett aure i lose access to the software wen my subscription expires but not 100% sure yet.

 

[Tinkerer]

Just to make things even more "interesting":

Keep in mind the possibility of measurement device error.

The Tactrix Openport 2.0 is a third-party diagnostic device. It may have "bugs" or erroneous protocol/data interpretation/reporting, especially for an uncommon proprietary system like AHC.

To be fair: I don't have a horse in this race - I got rid of AHC six months ago. (This thread illuminates one reason I got rid of it.)

Back to my day job.

 

[agaisin]

Just to make things even more "interesting":

Keep in mind the possibility of measurement device error.

The Tactrix Openport 2.0 is a third-party diagnostic device. It may have "bugs" or erroneous protocol/data interpretation/reporting, especially for an uncommon proprietary system like AHC.

Fair point! I have considered it - in fact even the techstream with supported devices has lots of defects, some of which include erroneous numbers etc...

Here's another question though - what pressure would you expect from failed Accumulators? Would the pressure still be within spec or would the pressure be through the roof?

In other words - is it possible to detect failed accumulators with the pressure readings? I've never seen anyone suggest this (wouldn't it be the easiest way to diagnose) so I'm doubtful - but if failed accumulators = through-the-roof pressure readings, then maybe that would explain the numbers.

I'm planning to take another look tonight to try to get the numbers within spec - basically I'll try to see what effect cranking tbars and adjusting height has on the pressure readings...

 

[lexi4darin]

If the accumulator (globe) failed, I'd expect the pressure to go down. I think this would be correct assumption based on the reports of "jouncy" rides after failed globe. Makes sense when you think the truck is riding more on the TB and rear coils with less dampening from failed hydraulic system.

 

[lexi4darin]

Also I'd expect to see the truck having trouble holding the height ... not a 1/2" difference between front or rear or DS/PS. But more like the front end is riding on the bump stops. Since you're not in that position (bump stops or the low low setting), I wouldn't expect catastrophic failure of your globes. At least not 100% fail yet.

 

[uHu]

Last thing first: The state of the accumulators will not affect AHC pressure. The AHC will just lift the vehicle until the sensors say the height is right. Doesn't matter if there is an accumulator there, or just a blank/cover.

Step one: The Neutral Pressure is the pressure when the vehicle has the correct height. Therefore you first have to get the height adjusted to spec (or another height you might fancy as the 'correct' height). This you do by adjusting the sensors.
Any lean is adjusted by cranking the T-bars.
When the vehicle is level, you should have approx the same value from both the front sensors. (AHC ECU adjusts height according to the average of the 2 fronts, but gives a fault status if the difference is too big.)

Then, after getting the height right, you can check the Neutral Pressure, and adjust the T-bars to suit. Crank same number of turns on both. (Check lean again if you have to adjust more than a few turns)

Now, I haven't looked into using an electronic tester for height/sensors and pressure, but it looks like it's telling you that the rear height is OK, but the pressure is too high. That normally means that you need new coils. According to my experience, that is normal for your years and miles. (Height less than 5 mm off. (2 mm is about 1/12 of an inch))

IIUC, the front sensors are misaligned. Your lean wouldn't be that big? Or maybe it is: That's about 1 inch. Remember that when the steering is straight, it's only the TBs (and stab.bar) which control the lean. Only at speed, in curves, the AHC valves would close off left and right to assist in reducing the outward lean. (At steering wheel angle more than 30 degees)

If those numbers mean that the front is too low, it could be because the TB's are too weak; and, looking at the high pressure reading, that the AHC cannot cope with the weight it is put to lift. If that is the case, it could be that you will not be able to adjust the sensors to achive correct height, but will have to crank the TBs a bit first. (Maybe it's enough to crank the side which is sagging)

(Continuing after a break...)

The electronic tester cannot actually see the pressure at each actuator/globe/sphere/accumulator, but measures the pump output press when the height has reached "Normal" on the axle being tested at the moment, but I suppose that's good enough. That's why there is a difference between the specified pressure when using the tester and when using a pressure gauge connected to the bleeder on the actuator. (like the LSPV-kit)
Also the height can easily be checked using a tape measure and the illustration and figures in the FSM. That's easy and fast, and reliable. I suggest double-checking the readings you got.


To sum up:
First get the height right, then get the pressure right.

Pressure depends on height: The higher you lift your truck, (using the AHC) the higher the pressure will be. Neutral pressure is what the gas-spheres (aka accumulators) are supposed to hold/lift when they are "resting" at normal vehicle height, and only then will the ride/damping/handling be optimal.

 

[agaisin]

OK - I got the pressure situation sorted out and can explain it too. (Front pressure is now 7 MPa and rear is 6.3 MPa - spec is for front to be 6.9MPa +-.5MPa, and for rear to be 5.6-6.7 MPa)

Here goes - when using the LSPV gauge, as uHu and others have noted in this and other threads it is the actual pressure at the globes and I learned through this exercise that the procedure for using LSPV is different than using Techstream/Handheld Tester. For one, with the LSPV gauge you want the vehicle off. With the Handheld tester/techstream you need the vehicle on.

When using the handheld tester or techstream, it is reading the pump's output pressure. Sounds easy enough. But here's what I realized:
- Start at H and then drop to N - techstream would read 0 MPa.
- Start at N and drop to L - techstream would read 0 MPa.
- Start at L and raise to N - techstream would read reasonable (close or within spec) MPa.
- Start at N and raise to H - techstream would read super high MPa.

So with Techstream, since it's reading the output pressure, you have to go from L to N and that's when you can use the pressure readings; if you go down in height, no pressure is output, just released, so you will not get a new reading and you'll be looking at the last pressure reading to raise the vehicle. I knew you were supposed to 'reset' height and I thought H to N or L to N would do the same thing - maybe for LSPV method, but not for techstream method. You have to go from L to N (and the FSM says to do that, but doesn't explain why). So in my case the first time I must have gone from L to H and then dropped to N and what I saw was really the pressure output to get to H and then when dropping to N, no pressure is output it just releases pressure to bring height down to N, so I was seeing the pressure reading from H instead of N.

Voila - so Tactrix OpenPort does seem to work just fine for reading AHC pressures and height sensors. (The input signal tests for AHC do not appear to work though, but active tests do work).

It turns out my pressure readings were within spec. My height is close enough I think - now I just need an alignment

Oh - and the -36mm on FL height sensor was b/c I was on very uneven sloped ground, I know stupid me. After cranking up an extra half turn and getting to even ground, the height on fl and fr is now within 2mm.

There are some things I'm not clear on with techstream and the height sensors, would love if someone could explain this....
- I understand how to measure them per FSM (for front it's spindle center height minus center of lower control arm bolt, for rear it's center of spindle height minus height of lower control arm bolt).
- I don't understand how to set the neutral position of the height sensor using the techstream/handheld tester approach - I expect it to be absolute but it looks like with techstream it's an override setting not absolute measurements?
- I don't understand what the reading on the height sensor means and if it is relative or absolute.
- there is a height offset utility that appears to allow you to override heights, I do not fully understand what it's intended use is. would love to understand better how to use it.
- In my case, for whatever reason, my front and rear sensors are at the lowest setting on the arm (the bolt is at the lowest setting on the vertical slot). The rear is ok in height, but the front is ~.25" too high - adjusting the threaded rod is a pita with the wheel on - I guess if I care enough I'll take the wheel off or take the sensor off. But my bigger question is that I would expect the bolt to be in the middle - perhaps techstream was used to override the height so that the bolt settings is now out of whack?

 

[agaisin]

OK - my height offset question rephrased:
Techstream has an AHC Utility called "Height Offset". I would like to confirm it's intended use and the procedure for using it.
I believe the purpose of this Utility is to set the neutral position of the height sensors which is described in the FSM under the Handheld Tester steps.

The Utility gives you the option of adjusting FR, FL, RR, or both Front wheels.
In every case it asks you for the measured value in inches, and asks you for the standard value in inches, and then it adjusts based on that.

The FSM provides the following measurements:
Measuring points:
A: Ground clearance of spindle center
B: Ground clearance of lower suspension arm front bolt center
C: Ground clearance of rear axle shaft center
D: Ground clearance of lower control arm front bolt center
Front A - B: 82.7 mm (3.256 in.)
Rear C - D: 71.2 mm (2.803 in.)

Let me run through two examples of how I think it's supposed to be used:
For FL sensor, I get 14.5" for A, 11" for B, so my measured value would be 3.5", and the standard value would be 3.25 (only allows two decimals to be entered). This should then raise the Front Left 1/4" to bring the B-A measurement to 3.25". Same for the FR.

For the Rear, if I have 14.5" for C, and 11.5" for D, then my measured value would be 3, and standard value 2.8, and I would expect the rear height to adjust up .2" to bring D-C value to 2.8.

Another question -> my height sensor adjusting bolts are at the bottom of the vertical slots and I have no down adjustment left, if I wanted to, shouldn't I be able to reset them to the center slot and then use the height offset utility to reset the height to what it needs to be without dicking with the manual adjustment of the sensor arms?

 

[lexi4darin]

Agaisin - good news so far. I'm going to look at the tester you got and see if it's worth the price. I haven't done my neut pressure test yet even tho I leveled the ride, adjusted TB's, did the flushes, etc.

I've also got a hankering to do my sway bushings so lots to do.

 

[agaisin]

Price was $169 + shipping. Of course to use Techstream you also need at least the $55 2 day professional subscription.

You may be able to find a used Tactrix cable - but I would only get the latest flavor - openport 2.0 since I don't know whether earlier versions supported all the same protocols plus I know from speaking with tech support that earlier versions were not the same quality.

 

[eleblanc]

The Tactrix Openport 2.0 is a third-party diagnostic device. It may have "bugs" or erroneous protocol/data interpretation/reporting, especially for an uncommon proprietary system like AHC.

I highly doubt this, the openport device and device drivers only serve as a communication protocol.

 

[agaisin]

I've been very pleased with the Tactrix cable and Techstream functionality. I also used it to reset steering angle and to perform zero point calibration as well (and all the ABS/VSC signal checks which is part of the procedure for zero point calibration...).

Only issue I had with it (limited use of course) is that I couldn't get it to perform the AHC Input Signal Check.

The height offset appears to work as I described above.

I have to say I was dissapointed in Techstream and TIS more than anything else since I couldn't find any true user documentation on meaning of fields and how to properly use the software. The FSM does not cover use of every capability in the software, in fact the FSMs from what I've seen only refer to handheld tester procedures (that could be through 2007 ish when the retired the handheld tester and introduced the Techstream software). As an example, the FSM doesn't talk about the height offset utility at all.

Anyhow, I would definitely recommend the Techstream + Tactrix combo based on my experience (albeit limited use so far).

<RANT>
I could write a lot on the topic based on tweaking and observation changes in the numbers - suffice it to say that even minor (.25") changes in height can take your neutral pressure out of spec. What I'm seeing now is that AHC is finicky - with the right tools/training it doesn't seem hard to keep it working well but without the right tools/training it's extremely easy to misdiagnose and waste tons of money. I shudder to think how many accumulator/globes have been replaced when they probably didn't need to be, and then furthermore how many might have been replaced without solving the root cause of failure by readjusting neutral pressure (i.e. if the first set was destroyed due to out of spec neutral pressure that will probably lead to premature failure of the second set too). I used to think that no give in the suspension = failed globes - it could, but I think it could also be neutral pressure too high which could be due to height too high for example. I am starting to give more weight to the 7 or more gradations test since iiuc the globes have give (gas filled portion) which means more volume is needed to raise the neutral pressure whereas when the globes are filled with fluid (i.e. membrane failed) less fluid is required to reach required height. Also, I've seen people notice that fluid level went down after failed globes - makes sense unless the reservoir was refilled - either way < 7 gradations makes sense to me that it would signify failed accumulators. On the other hand if someone is having a harsh ride but getting say 10+ gradations from L to H and no one corner is any stiffer than the others than I'd have to believe it's a neutral pressure issue (assuming suspension parts are all in order - wheel bearings, bushings etc).

Also, my impression is that zero point calibrations aren't performed as often as needed. I'm gonna go off on a limb and connect dots - people who have had ABS do f'n whacky things on the road like kick in and start braking the vehicle etc - could very well be due to lack of zero point calibration being performed? It's called for after any chassis/suspension change. VSC/ABS and AHC all work together! Bad inputs = bad outputs...
</RANT>

 

[agaisin]

For interest's sake, I think I see why Height Offset Utility is not mentioned in any LX470 documentation - in short the height offset utility was introduced for the LX570 in the very last version of the handheld software so it does not appear in any of the LX470 documentation. However Techstream allows it to be used for the LX470 and it appears to work. See below for more detail, and for LX570 and mastertech documentation on how to use it.

From the TIS site: "The Diagnostic Tester / Mastertech platform was the Toyota/Scion/Lexus factory scantool from 1993 to 2007. Our next generation scantool, TIS techstream, was released in 2007....The last Software release for the Toyota Diagnostic Tester was version 14.1 and was issued in April 2007"

See here for the Mastertech operators manual: http://www.boschdiagnostics.com/dso...Application_Operator's_Manual_-_worldwide.pdf
and here for the new features introduced up until the latest version 14.1:
http://www.google.com/url?sa=t&sour...xamSCw&usg=AFQjCNFmzHf0Sm9YQnrOkExQXNFh5bXijw

LX470's FSM only references the software/platform that was available at the time, the handheld tester. Even though techstream can be used on pre 2008 vehicles, there are no updates to the FSM for use with Techstream. For the most part it probably is almost exactly the same. I guess I happened to have come across one difference.

The New Features document above lists Height Offset Utility as a new feature that applies to the LX570. even though it appears to work with the LX470, it must have only been introduced for the LX570 in the very last version of of the software, hence no mention of it in the FSM for the LX470. I did find instructions on how to use it for the LX570, but not 100% sure how relevant some of the details are.

The New Features does give an example of its use and in their example they use (for the RR) 11.7 standard value and 11.8 as the measured value instead of 2.8 standard value and 2.7 measured value - meaning they're inputting the D value (center of rear control arm bolt) value from C-D rather than the C-D value (2.8"). I assume the utility works either way since the result is the same either way (.1").

Some other things mentioned in the LX570 FSM that I may be relevant for use on LX470 when inspecting height:
(a) Adjust the pressure of the tires.
(b) Stabilize the suspension by releasing the parking brake and bouncing the corners of the vehicle up and down.
(c) Start the engine.
(d) Perform the following operation twice:
Set the vehicle height to LO with the height control switch, and then return the vehicle height to NORMAL.
(e) Turn the engine switch off.
(f) Connect the Techstream to the DLC3.
(g) Move the shift lever to N and move the vehicle forward and rearward.
(h) Turn the engine switch on (IG) and the Techstream on.
HINT:
Make sure the engine is not running.
(i) Check that the vehicle height is NORMAL.
HINT:
The N of the multi-information display height control indicator in the combination meter turns on.
....

The possible vehicle height automatic adjustment value is 20 mm (0.787 in.). If the "Height Adjust value + (Standard value - Measurement value - After Height Adjust value)" is 20 mm (0.787 in.) or more, first perform the vehicle height adjustment for the front side and for the rear side.

 

[agaisin]

I wish I could find a level surface so I could be more confident in the numbers I get - anyone have ideas?

At this point I'm happy with close enough and better ride. But the geek in me wants more precision.

 

[agaisin]

Btw, can anyone interpret this step from the LX570 FSM for setting vehicle height:
(k) Using a jack, set the vehicle to the standard vehicle height and eliminate any difference in height between the left and right sides of the vehicle.

What does that mean "using a jack"? Are they saying to jack up the front and level L to R instead of trying to do it on the ground? If so, I think that's a very different approach - I had been tweaking TBs with the front jacked up to level L to R but then checking on the ground whether L to R is level rather than comparing L to R measurements while jacked up in the air. If that's what they're suggesting that would mean Rear lean and non level ground wouldn't factor into the L to R adjustment (i.e. simpler).

 

[lexi4darin]

I think the idea is that on level ground, you still want to alleviate some of the weight while torquing items such as sensors, TB, etc.

 

[agaisin]

Update on Offset Height Utility.

From experimenting again with it, I see that the New Features example using D (11.7) instead of C-D (2.8) as the measured value would be incorrect and what I posted above in Post 11 (https://forum.ih8mud.com/100-series-cruisers/485138-ahc-diagnostics-help.html#post6651864) is correct.

In other words, what I'm seeing is that you need to enter the C-D or A-B measured value, not the D or B value. As an example, if your rear is too low (D is 11.5 instead of 11.7), and you want to raise it, you would enter measured value of 3", standard value of 2.8, and your rear will raise to bring it to spec. If your rear is too high (D is 11.9 instead of 11.7) and you want to lower it, you would enter measured value of 2.6, standard value of 2.8, and your rear would lower to bring it to spec. Same concept for front. Hope this helps someone else.

(Btw, I don't know what it means to raise the FR different than the FL since based on every thing I've seen and others have seen, you can't raise FR or FL individually since the front valve is open under normal circumstances, asking the system to raise the FR .2 would presumably have the same effect as raising FR and FL each .1"...)