I just got a D7 allowing me to check my AHC pressures on my 05 LX470. Front pressure sensor is 10.7. rear pressure sensor 3.9. accumulator 10.8. From what I understand this means the front is high and the rear is low. Can someone please tell me how to correct this and what I should do?
AHC pressures
- Thread starter Magnaman
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GTV
SILVER Star
Yes, but without any other info on your truck its useless numbers to us.
Go read what @GTV posted. And watch the video in there also.
- Thread starter
- #5
Yes I've been reading. Once I hook up the D7 again I will post full numbers. I was looking at the pressures which I suspected were high.
GTV
SILVER Star
No because you measure from the center of the hub to the fender lip. Tire size does not matter.
- Thread starter
- #8
That's what I was thinking. I will do the calculations.
If you measure ground to fender, it changes by half the diameter... 2" larger OD on tire is +1" ground to fender. If you measure hub to fender, no, it would not change.
- Thread starter
- #10
So just measure hub to fender and ignore the tire size?
IndroCruise
SILVER Star
@Magnaman and @fdmarshal -- the above discussion is at cross-purposes concerning the effects of tire diameter on AHC pressures.
The position of the wheel hub with respect to the fender lip (or relative to any part of the vehicle) cannot and does not change due only to tires/wheels of different diameters being fitted. The Front Upper and Lower Control Arms and the Axle Hub remain unchanged in the same position relative to the chassis (and relative to the Fender Lip), regardless of tire diameter.
Tires/wheels of larger diameter than standard mean only that the hub will be higher from the ground surface and the tire/wheel will fill more of the wheel arch -- but the Control Arms and the Wheel Hub do not change position relative to the chassis and vehicle body when larger tires/wheels are fitted.
The Active Height Control (AHC) system and the Toyota Electronically Modulated Suspension (TEMS) system measures the position of the relevant Control Arm relative to the chassis, by using voltage signals from each of the Height Control Sensors (two in Front, one at the Rear) . The AHC/TEMS systems have no way of detecting different diameter wheels/tires.
As mentioned by the highly experienced @GTV, different wheel/tire diameters of themselves have zero effect on AHC pressures.
The Factory Service Manual (FSM) describes the detailed finnicky method for checking and setting vehicle heights relative to the ground, based on standard OEM tires.
Over the years, IH8MUD Members have used whatever tire/wheel arrangements they prefer -- and have found that hub-to-fender measurements of 19.75 inches (500 millimetres) at the Front and 20.50 inches (520 millimetres) at the Rear, measured with a tape-measure at "N" height and not with Techstream or other scanner, provide an excellent approximation of the correct hub position. This is the position at which the Height Control Sensors will be as close as possible to zero at "N" height as shown by Techstream or other scanner, and is the height to which the Active Height Control (AHC) system will cause the vehicle to 'actively' return, when "N" height is selected.
Different measurements to these hub-to-fender distances at "N" height WILL have an effect on AHC pressures -- larger hub-to-fender distances increase AHC pressure, lesser hub-to-fender heights reduce AHC pressure.
A Vehicle Owner can use the Height Control Sensor adjusters (not the Torsion Bar adjusters) to set a preferred vehicle height when "N" height is selected -- but must then make other adjustments to compensate for the effects on AHC pressures.
Last edited:
- Thread starter
- #12
This clarifies. Thank you.
- Thread starter
- #14
Okay guys here's what I got:
Front height L&R 19 3/4
Rear height L 21 R R 20.5
At Neutral height setting:
Rear Height Control -12.8
R Front Height Control 1.4
L Front Height Control 1.2
Front pressure 10.6
Rear Pressure 8.7
Accumulator pressure 10.6
Front height L&R 19 3/4
Rear height L 21 R R 20.5
At Neutral height setting:
Rear Height Control -12.8
R Front Height Control 1.4
L Front Height Control 1.2
Front pressure 10.6
Rear Pressure 8.7
Accumulator pressure 10.6
GTV
SILVER Star
You are the AHC guru.
IndroCruise
SILVER Star
Results by @Magnaman for 2005 LX470 in Arizona and discussion:
Hub-to-fender distances -- done at "N" height?
Front height L&R 19 3/4
-- good, same on both sides, Front Cross-Level is good.
Rear height L 21 R R 20.5
-- LHS Rear is sitting 0.5 inches high, if chassis and body are true (not twisted, vehicle sitting on a level surface -- not driveway, not street), might expect diagonally opposite RHS Front to be 0.5 inches low. Result may be affected by damage or wear somewhere, such as worn springs or spring seats/packers, or worn 'shock absorber' bushes (Note: In AHC system the 'shock absorbers' -- which really are just simple hydraulic struts -- carry their share of vehicle weight at all times including when vehicle is at rest, different to shock absorbers in a conventional suspension). As an indication, the difference is within the FSM-specified tolerance of 0.39 inches (10 millimetres) for Front cross-level, so suggest that it is reasonable to assume a similar tolerance at the Rear, and if so, it not worthwhile to 'pursue perfection' at the Rear. There are other faults to fix first.
AHC Height Control Sensor readings at "N" height setting:
R Front Height Control Sensor 1.4
-- good, close to zero,
L Front Height Control Sensor 1.2
-- good, close to zero,
Rear Height Control Sensor -12.8
-- not good, difference from other Sensors is much too large. When there is a large difference, the Suspension Electronic Control Unit (ECU) cannot resolve the correct height signal for "N" height and the vehicle may behave erratically. The ECU may place the AHC/TEMS systems in "Fail Safe Function" -- if so, this prohibits AHC/TEMS operation. There may or may not be a Diagnostic Trouble Code (DTC C1713) appearing for the Rear Sensor -- only happens if the signal is out of the FSM-specified voltage range, does not happen if the signal is within the FSM-specified range but the vehicle height is incorrect. In the case of your vehicle, the Rear tape-measured hub-to-fender distance is reasonable but the signal is unsatisfactory when read on Techstream or other scanner -- where it is displayed in inches or millimeters, not volts. CONCLUSION: The result for the Techstream or scanner result for the Rear Height Control Sensor circuit (meaning Sensor plus Connector plus Harness) is way out of order. The condition of the Sensor and/or its connector and/or its harness is suspicious. SUGGEST remove the Sensor from vehicle, inspect connector, wiring harness -- then remove cover from Sensor itself, inspect, clean AND TEST PER FSM. (Note: Inspection is not enough -- Sensor faults cannot be detected reliably by eye). Alternatively, if confident of connector and harness, replace the Rear Height Control Sensor with new OEM Toyota/Lexus Height Control Sensor Part Number 89407-60010 from IMPEX or PARTSOUQ (or Toyota or Lexus Dealer if the price is right) -- avoid substitutes if reliability and longevity are important.
AHC Pressure readings at after moving from "LO" height to "N" height, at correct hub-to-fender distances, Fuel Full, no load nor persons in vehicle -- best to make readings and subsequent adjustments with all permanent accessories and builds in place -- but achieve front and Rear AHC pressures in the FSM-specified ranges:
Front pressure 10.6
-- way too high, FSM-specified range is 6.4 to 7.3 MPa, maybe vehicle is heavy at the Front (?) or maybe it is long overdue to for AHC review and adjustment (?) - needs a LOT of Torsion Bar adjustment -- gives about 0.2 Mpa per turn of Torsion Bar adjuster means 15 to 20 turns (?), so you may run out of thread on the adjusting bolt and re-indexing the Torsion Bars may be necessary to achieve correct Front AHC pressure.
Rear Pressure 8.7 (mentioned 3.9 MPa in Post #1 this thread???)
-- way too high, FSM-specified range is 5.6 to 6.7 Mpa -- maybe vehicle is heavy at the Rear (?) or maybe it is long overdue to for AHC review and adjustment (?) -- pre-loading with packers/spacers will be insufficient, needs coil springs with a higher spring rate, suggest King KTRS-79 which would give the required correction of about 3 Mpa.
Accumulator pressure 10.6
-- normal
Factory Service Manual (FSM):
In addition to the link provided by provided by @GTV at Post #4 this thread and in addition to the "Search" function on IH8MUD ....
Ideally, obtain and use the 2005 LX470 Factory Service Manual but if this is not to hand, suggest use the following links to Land Cruiser 100 series FSM -- the AHC/TEMS sections for specifications, diagnosis and repair & maintenance guidance are the same for both LX470 and LC100 (where AHC/TEMS is fitted).
General Description of the AHC/TEMS systems with explanations and diagrams of components -- this is an excellent read if not seen before, worth printing for later reference:
LC100 Workshop Manual - https://lc100e.github.io/,
then scroll down through the index panel on the LHS of the opening page:
+ New Car Features
+ CHASSIS
+ Suspension
+ Active Height Control and Skyhook TEMS
Scrolling to “Repair Manual” and “DIAGNOSTICS” reveals relevant diagnostic and test information, etc. For example:
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS
Scrolling to Electrical Wiring Diagram and visually tracing the circuits helps with understandings of how things work:
LC100 Workshop Manual - https://lc100e.github.io/
+ Electrical Wiring Diagram
+ OVERALL ELECTRICAL WIRING DIAGRAM (RHD)
+ Active Height Control Suspension
+ Choose relevant year -- note: there can be some differences in EWD's for LC100 and LX470
The coloured EWD is better -- found at Post #420 at this thread:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-21#post-14909889
Scrolling to “Repair Manual” reveals settings, repair information etc. For example:
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ SUSPENSION AND AXLE
+ ACTIVE HEIGHT CONTROL SYSTEM
+ ON-VEHICLE INSPECTION
Hub-to-fender distances -- done at "N" height?
Front height L&R 19 3/4
-- good, same on both sides, Front Cross-Level is good.
Rear height L 21 R R 20.5
-- LHS Rear is sitting 0.5 inches high, if chassis and body are true (not twisted, vehicle sitting on a level surface -- not driveway, not street), might expect diagonally opposite RHS Front to be 0.5 inches low. Result may be affected by damage or wear somewhere, such as worn springs or spring seats/packers, or worn 'shock absorber' bushes (Note: In AHC system the 'shock absorbers' -- which really are just simple hydraulic struts -- carry their share of vehicle weight at all times including when vehicle is at rest, different to shock absorbers in a conventional suspension). As an indication, the difference is within the FSM-specified tolerance of 0.39 inches (10 millimetres) for Front cross-level, so suggest that it is reasonable to assume a similar tolerance at the Rear, and if so, it not worthwhile to 'pursue perfection' at the Rear. There are other faults to fix first.
AHC Height Control Sensor readings at "N" height setting:
R Front Height Control Sensor 1.4
-- good, close to zero,
L Front Height Control Sensor 1.2
-- good, close to zero,
Rear Height Control Sensor -12.8
-- not good, difference from other Sensors is much too large. When there is a large difference, the Suspension Electronic Control Unit (ECU) cannot resolve the correct height signal for "N" height and the vehicle may behave erratically. The ECU may place the AHC/TEMS systems in "Fail Safe Function" -- if so, this prohibits AHC/TEMS operation. There may or may not be a Diagnostic Trouble Code (DTC C1713) appearing for the Rear Sensor -- only happens if the signal is out of the FSM-specified voltage range, does not happen if the signal is within the FSM-specified range but the vehicle height is incorrect. In the case of your vehicle, the Rear tape-measured hub-to-fender distance is reasonable but the signal is unsatisfactory when read on Techstream or other scanner -- where it is displayed in inches or millimeters, not volts. CONCLUSION: The result for the Techstream or scanner result for the Rear Height Control Sensor circuit (meaning Sensor plus Connector plus Harness) is way out of order. The condition of the Sensor and/or its connector and/or its harness is suspicious. SUGGEST remove the Sensor from vehicle, inspect connector, wiring harness -- then remove cover from Sensor itself, inspect, clean AND TEST PER FSM. (Note: Inspection is not enough -- Sensor faults cannot be detected reliably by eye). Alternatively, if confident of connector and harness, replace the Rear Height Control Sensor with new OEM Toyota/Lexus Height Control Sensor Part Number 89407-60010 from IMPEX or PARTSOUQ (or Toyota or Lexus Dealer if the price is right) -- avoid substitutes if reliability and longevity are important.
AHC Pressure readings at after moving from "LO" height to "N" height, at correct hub-to-fender distances, Fuel Full, no load nor persons in vehicle -- best to make readings and subsequent adjustments with all permanent accessories and builds in place -- but achieve front and Rear AHC pressures in the FSM-specified ranges:
Front pressure 10.6
-- way too high, FSM-specified range is 6.4 to 7.3 MPa, maybe vehicle is heavy at the Front (?) or maybe it is long overdue to for AHC review and adjustment (?) - needs a LOT of Torsion Bar adjustment -- gives about 0.2 Mpa per turn of Torsion Bar adjuster means 15 to 20 turns (?), so you may run out of thread on the adjusting bolt and re-indexing the Torsion Bars may be necessary to achieve correct Front AHC pressure.
Rear Pressure 8.7 (mentioned 3.9 MPa in Post #1 this thread???)
-- way too high, FSM-specified range is 5.6 to 6.7 Mpa -- maybe vehicle is heavy at the Rear (?) or maybe it is long overdue to for AHC review and adjustment (?) -- pre-loading with packers/spacers will be insufficient, needs coil springs with a higher spring rate, suggest King KTRS-79 which would give the required correction of about 3 Mpa.
Accumulator pressure 10.6
-- normal
Factory Service Manual (FSM):
In addition to the link provided by provided by @GTV at Post #4 this thread and in addition to the "Search" function on IH8MUD ....
Ideally, obtain and use the 2005 LX470 Factory Service Manual but if this is not to hand, suggest use the following links to Land Cruiser 100 series FSM -- the AHC/TEMS sections for specifications, diagnosis and repair & maintenance guidance are the same for both LX470 and LC100 (where AHC/TEMS is fitted).
General Description of the AHC/TEMS systems with explanations and diagrams of components -- this is an excellent read if not seen before, worth printing for later reference:
LC100 Workshop Manual - https://lc100e.github.io/,
then scroll down through the index panel on the LHS of the opening page:
+ New Car Features
+ CHASSIS
+ Suspension
+ Active Height Control and Skyhook TEMS
Scrolling to “Repair Manual” and “DIAGNOSTICS” reveals relevant diagnostic and test information, etc. For example:
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS
Scrolling to Electrical Wiring Diagram and visually tracing the circuits helps with understandings of how things work:
LC100 Workshop Manual - https://lc100e.github.io/
+ Electrical Wiring Diagram
+ OVERALL ELECTRICAL WIRING DIAGRAM (RHD)
+ Active Height Control Suspension
+ Choose relevant year -- note: there can be some differences in EWD's for LC100 and LX470
The coloured EWD is better -- found at Post #420 at this thread:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-21#post-14909889
Scrolling to “Repair Manual” reveals settings, repair information etc. For example:
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ SUSPENSION AND AXLE
+ ACTIVE HEIGHT CONTROL SYSTEM
+ ON-VEHICLE INSPECTION
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- Thread starter
- #17
Thank you! I've got my work cut out for me, don't I? Yes the measurements were taken at the N height setting on a flat concrete pad. I will check the rear height sensor as you suggested. I presume my front pressure is way too high as well? For the record, the AHC works, meaning it moves from low to neutral to high. The TEMS I'm not so sure about. I have no AHC codes, in fact the only codes I have are a PO420 that I'm working on. I find that driving over over washboard and bad roads the suspension feels too stiff. I can't remember the exact numbers at the moment but I checked the gradation changes in the fluid tank and they were good. I changed the AHC fluid three or four years ago.
However, I got started on this a couple of years ago when I noticed a bit of leakage in my front shocks. I assumed I needed new shocks, not understanding that these are not really shocks. I posted something here and was told my pressures were probably too high, not that the "shocks" were bad. I got one of those adapters off of eBay for Techstream, but I could not for the life of me get it to work on my laptop so I gave up. Now, I have the scanner and for the first time I can read the AHC live data. So here I am.
IndroCruise
SILVER Star
- "I presume my front pressure is way too high as well?" Definitely Yes -- as menioned in my Post #17 above. This over-pressure is a recipe for internal seals leaking in the 'shock absorbers'. Unless seals have been permanently damaged by long term over-pressure, leaks may stop when AHC pressures are corrected.
- Given the AHC pressures reported, it is unsurprising that ".... driving over over washboard and bad roads the suspension feels too stiff". At your AHC pressures, damping and 'ride quality' are compromised. This will improve when Front and Rear AHC pressures are corrected into the FSM-specified ranges and damping can operate correctly as designed.
- Good that AHC is still working -- means that the ECU has not initiated "Fail Safe Function" and caused AHC/TEMS prohibitions -- so maybe TEMS is working as well. To confirm that TEMS is working, drive (safely) with your scanner connected. If your scanner displays something similar to "Front Wheel Step" and "Rear Wheel Step", also "Damping Force Switch 1" and "Damping Force Switch 2", then you should be able to see differences while driving and also see the effects of changing the COMFORT switch on the Centre Console through its four positions. This should show the variations in up to 16 steps in damping positions which the ECU (TEMS) can adopt in real time. When stopped or in "Fail Safe Mode" TEMS will default to Step 8 and there will be no adaptive damping with different road conditions.
- It is worth remainings suspicious of the Rear Height Sensor circuit (not just the Sensor), as the ECU does not distinguish between faults in the Sensor, or the Connectot, or the Harness. It is common for a fault to arise which causes the wrong voltage signal for the actual height of the vehicle to be sent to ECU -- but the signal remains within the range of 0.3 Volts to 4.7 Volts accepted by by the ECU. In this situation, no DTC is recorded (because the signal is within range accepted by the ECU) even though there is a fault somewhere in the Sensor circuit or in the Sensor itself -- such as when the circuit is shortened in some way, lowering resistance and affecting the signal voltage. Diagnosis of Height Control Sensor circuit faults also requires observation of the behaviour of the vehicle -- especially when Height Control Sensor circuit readings on Techstream or other scanner are inconsistent with the physical tape-measured hub-to-fender distances -- as in the case of your vehicle. This is one of the limitations of the AHC/TEMS Diagnostics.
Bonjour,
Merci pour toutes ces informations, qui me permettent de maintenir la suspension AHC de mon Land Cruiser 100 diesel de 2004 avec 227 000 km au compteur en parfait état !
Deux questions, s'il vous plaît :
La pression à l'avant est correcte (6,8 MPa). La pression à l'arrière est un peu élevée (6,8 MPa). Je vais donc utiliser des entretoises de 30 mm pour l'abaisser. Connaissez-vous le couple de serrage de l'écrou inférieur de l'amortisseur ?
Je ne constate aucune différence entre les modes d'amortissement « confort » et « sport ». Quelle pourrait en être la cause ?
Pour information, le capteur avant droit est à 1,8 mm, le gauche à -1 mm et le capteur arrière à 1 mm. La hauteur des moyeux de roue est correcte (500 mm à l'avant, 520 mm à l'arrière), les sphères de suspension sont neuves (14 points au test) et le liquide de suspension AHC a été changé.
Merci pour vos commentaires.
Merci pour toutes ces informations, qui me permettent de maintenir la suspension AHC de mon Land Cruiser 100 diesel de 2004 avec 227 000 km au compteur en parfait état !
Deux questions, s'il vous plaît :
La pression à l'avant est correcte (6,8 MPa). La pression à l'arrière est un peu élevée (6,8 MPa). Je vais donc utiliser des entretoises de 30 mm pour l'abaisser. Connaissez-vous le couple de serrage de l'écrou inférieur de l'amortisseur ?
Je ne constate aucune différence entre les modes d'amortissement « confort » et « sport ». Quelle pourrait en être la cause ?
Pour information, le capteur avant droit est à 1,8 mm, le gauche à -1 mm et le capteur arrière à 1 mm. La hauteur des moyeux de roue est correcte (500 mm à l'avant, 520 mm à l'arrière), les sphères de suspension sont neuves (14 points au test) et le liquide de suspension AHC a été changé.
Merci pour vos commentaires.