The ABCs of AHC - How to Measure, Flush, and Adjust all in one place
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I have new globes and am pretty close to spec w my pressures, but since the new globes were installed the lowering from N to L is a bit "herky jerky" compared to the smooth motion prior to installing the new globes. Any ideas what might cause this? Could it be that the system wasn't properly bled with the install?
ramangain
Clarksonian disciple
Well worth reposting for those wanting to learn more about AHC: Technical PDF about AHC functionality
IndroCruise
SILVER Star
I was confused about this also. The TB’s are used for cross leveling to change height but actual height is done by the sensors IE AHC lift.
It also took me a while to learn how the AHC/TEMS systems work from uHu, PADDO and many other IH8MUD Members who had gone before -- and I am still learning and in need of being steered in the right direction
. The attached Explanatory Notes may be helpful. They add to the earlier replies. Hopefully they are not confusing. Some relevant short FSM extracts also are attached for convenience.
The third attachment deals with the actual FSM Height Specification measurements at "N" height and are attached for interest. These are finicky to measurements and have led to the more practical approximation by IH8MUD Members of the hub-to-fender measurements of Front 19.75 inches and Rear 20.5 inches (or 500 millimetres and 520 millimetres respectively). These 'measurements' are now widely used to good effect but we cannot say that they come from the FSM -- because they don't. However, the approximations do work very well.
Use of these approximations is supported by Height Control Sensor Measurements of close to zero being achieved.
Late edit – additional information:
A perusal of the AHC Diagnostic section of the FSM and some following posts at this link give an idea of various fault conditions which can arise. This is heavy reading and some of the electrical circuits and other information can be a bit dazzling -- at least for me! However, even for a non-electrical person, a skim through the part of the FSM attached at the link does indicate how the AHC/TEMS system may behave in the case of various faults.
For example: Problems with the Height Control Sensor Circuit are experienced by many vehicles and it can be difficult to understand what the AHC/TEMS is doing in the case of this fault. This part of the FSM includes the following advice about the Height Control Sensor Circuit:
Circuit Description:
Inside each sensor, a brush integrated with the control sensor rotor shaft moves above the resistor, proving linear output. The resistance value between the brush and resistor terminal changes in proportion to the shaft rotation angle, so the fixed voltage applied to the resistor by the ECU is modified by the sensor and output to the ECU as a voltage indication the shaft rotation angle.
Fail safe function:
If a trouble occurs in the height control sensor circuit, the height control is prohibited after the ECU has adjusted the vehicle height to the standard (fluid pressure correspond to the standard height).
[In other words, the AHC/TEMS system will not operate properly if this fault is experienced. The FSM and some of the posts by uHu and others following the above link explain what can be done in this situation. The section of the FSM at the above link also describes various other fault conditions and the operational prohibitions which arise in each case. This helps in diagnosis].
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Thanks so much for this post!! I just knocked out my 06 AHC baseline (truck just hit 60k miles). I did have a question: all my numbers everything turned out great but the front right height is -7.1mm. Not showing on the garage is the rear left height at -7mm . Should I adjust these as close to 0mm as possible or leave as is?
IndroCruise
SILVER Star
The comments and screenshot from your scanner are a little bit confusing – there is only one rear Height Control Sensor.
Just to be clear about the on-vehicle inspection/adjustment steps which must be done in this order (1) to (11) -- without skipping any steps …..
- ‘Cross-level’ with the engine/AHC “OFF”. The purpose of this step is to ensure that each front torsion bar is carrying equal loads by making the Left and Right hub-to-fender measurements equal with tape-measure with engine/AHC “OFF” by turning torsion bar adjusters. Do not worry about the actual measurement numbers in this step – just make them equal. To avoid running out of thread on the torsion bar adjusters, ‘cross-level’ by turning adjusters equal turns in opposite directions until equal, front Left = front Right, within 10 millimetres (0.39 inches) with engine/AHC “OFF”.
- Set correct operating Left and Right hub-to-fender measurements with the Height Control Sensor adjusters (NOT the torsion bar adjusters). In this step, measure with the engine/AHC “ON” – but turn engine/AHC “OFF” for safety when actually making changes at the Height Control Sensor adjusters. Turn engine/AHC “ON” to check progress. Rock vehicle, or drive up and down driveway, or drive around the block to allow suspension to settle in new position. Re-check Left and Right operating hub-to-fender measurements again with engine/AHC “ON”. Repeat this step until satisfied with correct operating Left and Right hub-to-fender measurements with tape-measure: Front 19.75 inches, Rear 20.5 inches.
- Attach Techstream or scanner and check front and rear pressures according to the FSM-prescribed procedure. Do NOT do this step until ‘cross-levelling’ (to equalise torsion bar loads) and operating hub-to-fender tape measurements are all correct.
- When ‘cross-levelling’ and operating front hub-to-fender measurements are all correct, turn torsion bar adjusters equal turns in same direction to achieve front AHC pressure within FSM-specified range.
- When ‘cross-levelling’ and operating front hub-to-fender measurements and front AHC pressure are all correct, read Height Control Sensor values on Techstream or scanner.
- Front Height Control Sensor values on Techstream/scanner should be close to zero (within 5 millimetres or 0.20 inches). It is possible to turn the Height Control Sensor thread adjusters a little to improve the values BUT be aware that widely different front values may be indicating faults in the Height Control Sensors or may be indicating some other suspension problem.
- In the case of wide differences from Height Control Sensor readings on Techstream or scanner, it is suggested that the Sensors be removed and inspected externally and internally and also tested electrically per FSM recommendations. An underbody check of suspension wear parts also is suggested.
- If Rear AHC pressures are high, consider spacers or replacement springs or stronger springs.
- Check external, internal and electrical condition of Rear Height Control Sensor and underbody condition if values on Techstream or scanner are not close to zero.
- When front and rear hub-to-fender measurements and front and rear AHC pressures are correct, then conduct HI/LO Test to check condition of ‘globes’: Near new = 14 graduations; need replacement = 7 graduations. Note that correct AHC pressures tells NOTHING about the condition of 'globes'.
- Test drive vehicle and decide whether ride quality is satisfactory.
Performed an AHC fluid flush today. The following attachments are AHC pressures Pre-flush, Post-flush, and Post-flush with Temp Sensor Disconnected. In the rear i added 30mm coil spacers before doing pressure measurements this morning. When i performed the reservoir level check Pre-flush it was just over 7 graduations low to high. I forgot to check to see if my low to high graduation count changed post flush, but i will add that info here in the morning. Tomorrow i am going to tighten my torsion bars to lower my front pressures.
If i understand pressure adjustment the process correctly, i need five full clockwise turns on each torsion bar to bring my the front to pressure down from 7.9 MPa to 6.9 MPa ( 0.2 MPa change in pressure per full turn of a TB nut)
My question is what will happen to my rear pressures as a side effect of tightening the front torsion bars, and should i use the pressure reading of 7.3 (reading with temp sensor connected)-picture two
or pressure reading of 6.1 (reading with temp sensor disconnected)-picture three
Expert input will be greatly appreciated.
If i understand pressure adjustment the process correctly, i need five full clockwise turns on each torsion bar to bring my the front to pressure down from 7.9 MPa to 6.9 MPa ( 0.2 MPa change in pressure per full turn of a TB nut)
My question is what will happen to my rear pressures as a side effect of tightening the front torsion bars, and should i use the pressure reading of 7.3 (reading with temp sensor connected)-picture two
or pressure reading of 6.1 (reading with temp sensor disconnected)-picture three
Expert input will be greatly appreciated.
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- Thread starter
- #89
Some find adjusting the front affects the rear very little. It can occasionally increase/decrease pressures depending on how significant a change you have to make. I'd guess yours won't change too much after adjustment.
Take two or three readings each with temp sensor connected and disconnected. If they're a lot different on average, use the disconnected value.
Take two or three readings each with temp sensor connected and disconnected. If they're a lot different on average, use the disconnected value.
Excellent
Thanks for the reply and Thanks very much for starting and monitoring this thread. I will update tomorrow after adjusting the torsion bars.
Also i noticed on techstream data when going from neutral to high the front raises 1.6", rear 1.9" but when going neutral to low the front goes down 1.9" and the rear down 1.6". Is this normal?
Update:
Measured the low to high graduations in the reservoir and they are pretty much unchanged at 7+ to barely 8 ish.
Put 5 full clockwise turns on the front torsion bars. Post torsion bar tightening dropped the front pressure exactly as prescribed .2 per full turn resulting in pressure going from 7.9 to 6.9 in the front. The rear now reads 6.8 with temp sensor connected and 6.1 with temp sensor disconnected. My photo with temp sensor disconnected did not come out good so i just have the one photo below with temp sensor connected.
It seems i'm good to go for a while with my AHC now and next step with be a full alignment, wheel balancing, and rotation. I have a little vibration in the front around 73ish on the highway to sort out.
Thanks again LndXrsr for your effort and detailed information.
Kevin
Thanks for the reply and Thanks very much for starting and monitoring this thread. I will update tomorrow after adjusting the torsion bars.
Also i noticed on techstream data when going from neutral to high the front raises 1.6", rear 1.9" but when going neutral to low the front goes down 1.9" and the rear down 1.6". Is this normal?
Update:
Measured the low to high graduations in the reservoir and they are pretty much unchanged at 7+ to barely 8 ish.
Put 5 full clockwise turns on the front torsion bars. Post torsion bar tightening dropped the front pressure exactly as prescribed .2 per full turn resulting in pressure going from 7.9 to 6.9 in the front. The rear now reads 6.8 with temp sensor connected and 6.1 with temp sensor disconnected. My photo with temp sensor disconnected did not come out good so i just have the one photo below with temp sensor connected.
It seems i'm good to go for a while with my AHC now and next step with be a full alignment, wheel balancing, and rotation. I have a little vibration in the front around 73ish on the highway to sort out.
Thanks again LndXrsr for your effort and detailed information.
Kevin
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I finally changed my AHC fluid today. I ordered four of the bottles from Toyota, I know it takes less, but once I get into something I don't want to have to wait for SO parts. It's probably about as easy as changing your oil, a little more crawling around, but just as easy. I have about 192k miles on my LX base model, and I have records showing it was last changed 100k miles ago. The fluid was green as everyone has stated, and I ended up using just over three bottles. I probably over did it, but I had the extra. It ran pink out of all 5 bleeders. Total time maybe 45 minutes, and most of that was setting up.
Before changing the fluid I could feel every new section of road, the seams, and I thought that was normal because my 60 rode like that. Well, after the fluid change, I can no longer feel them. The ride is smooth. Oh, also before changing the fluid I had 10 ticks between L and H. My rig has zero rust so there was no need to pre-lube anything.
Thank you all for posting your experiences! You truly made my life easier!
Before changing the fluid I could feel every new section of road, the seams, and I thought that was normal because my 60 rode like that. Well, after the fluid change, I can no longer feel them. The ride is smooth. Oh, also before changing the fluid I had 10 ticks between L and H. My rig has zero rust so there was no need to pre-lube anything.
Thank you all for posting your experiences! You truly made my life easier!
@kpecks what app is that your'e using?
OBDLink. I am using the bluetooth OBDlink MX+ for iOS. Im pretty happy with it and it works with well with my android head unit.
@LndXrsr this may sound like a silly question, but my 2006 LC has the fender flares installed. Does that make a difference as to how I measure my heights i.e. do I still go from center of wheel cap to the flare lip? thank you.
- Thread starter
- #95
if they line up with the metal wheel well lip then no difference. If they’re higher than you’ll need to add the difference into your measurements.
thank you!
So i installed my ARB front bumper and figured it probably added pressure to my system. Went back to tech stream and did some cranking and now I'm just about back at 6.9
However, it maxed out one of my t bars. Can't turn the bolt any more.
Is there any danger or affect on performance in maxing these things out?
However, it maxed out one of my t bars. Can't turn the bolt any more.
Is there any danger or affect on performance in maxing these things out?
ramangain
Clarksonian disciple
Yes. Your interwebz may break until you reindex the offending tbar.
No problem, but you may want to re-index that bar eventually. You just need to take it out, turn it a tiny bit and reinstall. It's much more difficult to actually do, but that's all there is to it. Just have to mark it, remove, twist one spline, reinstall.
damn then I need to reindex my interwebz huh
Cool thanks. I'm hovering around 7.2 in the front so maybe I'll reindex down the road
Regarding the back, I'm at about 7.9 with a roof rack, RTT, and drawers in the back. I'm definitely not at the weight for King springs, but what's the latest thought with that kind of pressure? Replace with OEM AHC coils? Replace coils and add a spacer? Just add a spacer to my original springs?