Ahc 2006 LX470 leak. (1 Viewer)

[BOB F]

I’ve replaced a couple corroded lines a few years ago and I have a new leak. It’s inboard of the accumulated on the left side.

There’s a stain on the driveway and I can see where it’s wet visually. The problem is I can’t reproduce it on demand. The height control works but it doesn’t leak when I do that. It doesn’t leak all the time.

what am I missing here? How can I activate that particular line to identify the source of the leak?
Thanks

 

[IndroCruise]

I’ve replaced a couple corroded lines a few years ago and I have a new leak. It’s inboard of the accumulated on the left side.

There’s a stain on the driveway and I can see where it’s wet visually. The problem is I can’t reproduce it on demand. The height control works but it doesn’t leak when I do that. It doesn’t leak all the time.

what am I missing here? How can I activate that particular line to identify the source of the leak?
Thanks

If inboard of the Height Control Accumulator, do you have reason to suspect pipes or joiners to/from the Control Valve Assembly which is on the inboard side of the Left chassis rail at a similar location as the Accumulator? If so, would operating the suspension functions using the Active Test procedure help to reveal the leak location? Ideally with the wheels on a hoist if you have access to one, so that you can get underneath safely with a torch while an assistant does the Active Test. Obviously wear eye protection and be very careful so that you don't get an eyeful!

 

[BOB F]

If inboard of the Height Control Accumulator, do you have reason to suspect pipes or joiners to/from the Control Valve Assembly which is on the inboard side of the Left chassis rail at a similar location as the Accumulator? If so, would operating the suspension functions using the Active Test procedure help to reveal the leak location? Ideally with the wheels on a hoist if you have access to one, so that you can get underneath safely with a torch while an assistant does the Active Test. Obviously wear eye protection and be very careful so that you don't get an eyeful!

Hi and thank you.

That is the suspect area and block. How to I find info on how to run the active test?

 

[IndroCruise]

Hi and thank you.

That is the suspect area and block. How to I find info on how to run the active test?

https://lc100e.github.io/manual/ (LC100 Factory Service Manual)
Then follow index tabs at top left of opening page:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > PRE-CHECK

Look for
Page DI-214 Item 5. HEIGHT CONTROL OPERATION TEST (ACTIVE TEST)

The attachment for LX470 also covers the same test at the last page but instead of DLC3 uses DLC1 in the engine bay -- which generally is easier.

As seen in the pic below, there are a lot of pipes in this area – not all connected to the Control Valve Assembly.

 

[BOB F]

https://lc100e.github.io/manual/ (LC100 Factory Service Manual)
Then follow index tabs at top left of opening page:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > PRE-CHECK

Look for
Page DI-214 Item 5. HEIGHT CONTROL OPERATION TEST (ACTIVE TEST)

The attachment for LX470 also covers the same test at the last page but instead of DLC3 uses DLC1 in the engine bay -- which generally is easier.

As seen in the pic below, there are a lot of pipes in this area – not all connected to the Control Valve Assembly.

View attachment 2679428

View attachment 2679439

 

[BOB F]

That is the area that is wet with fluid. Thank you and I’ll work through the test if I can.

 

[IndroCruise]

That is the area that is wet with fluid. Thank you and I’ll work through the test if I can.

Thinking a bit more about how to expose the pipe(s) which is (are) causing leaks ….

It also may help to go to this reference
https://lc100e.github.io/ (LC100 Factory Service Manual) -- link update June 16, 2024.
Then follow index tabs starting at the top left of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control & Skyhook TEMS

This opens to a 20 page general description of the Active Height Control (AHC) system and the Toyota Electronic Modulated Suspension (TEMS) system and how they operate.

The document shows simplified schematics of the AHC hydraulic circuit under various conditions.

This document and the following notes may help to visualise where and when pressures are developing in the AHC system and this may help in the search for leaks – or it may confuse!!

A quick look at the cross-section at 11 pages into the document (labelled Page 206) shows which of the four pipes at the top of the Control Valve Assembly is connected to which valve.

A fifth pipe enters the Control Valve Assembly at the forward end – this is the connection to the Height Control Accumulator on the other side of the chassis rail. The pipe from the AHC Pump also joins the circuit at the front end of the Height Control Accumulator.

The flow diagram at 18 pages into the document (labelled Page 213) shows what is happening when the vehicle is raised from LO to N (and then on to HI).

First, the solenoid valve at the Height Control Accumulator is opened by the ECU. It releases pressure and fluid, causing the vehicle to raise. When all components are in good condition with AHC pressures within the FSM-specified ranges, vehicle at specified height and at specified weight condition, the Height Control Accumulator is meant to contain sufficient pressure and volume to raise the vehicle and then is re-charged by the AHC Pump.

Clearly, system pressures rise to their maximum during the process of raising the vehicle – no surprise here!

While this is happening, the Front and Rear Levelling Valves open and close sequentially under ECU control as the vehicle shuffles upwards. These valves are below the two outer-most pipe connections at the top of the Control Valve Assembly. These valves also are meant to prevent fluid returning to the AHC tank – unless LO height is selected.

Leakage associated with the pipes and connections to the Front and Rear Levelling Valves, and to the pipe and connections between the Control Valve Assembly and the Height Control Accumulator would be expected to be most prominent during the process of raising the vehicle.

Long term serious leakage from the Front or Rear Level Levelling Valves (say when the vehicle is left standing for days/weeks) would result in the vehicle losing height.

This may not be particularly noticeable during brief stoppages because the ECU would respond to the Height Control Sensors and cause the AHC Pump to operate and auto-adjust the vehicle to the height selected on the centre console. Eventually, fluid loss would be noticeable at the AHC Tank.

It is all a bit different with the Gate Valves in the Control Valve Assembly. These are open when the vehicle is stationary or when the steering is straight ahead. The Gate Valves are only closed by the ECU in response to combinations of inputs such as steering wheel angle during turns, wheel speed, brakes, and possibly other inputs. The Gate Valves are below the two inner-most pipe connections at the top of the Control Valve Assembly. It is not possible to observe different side-to-side Gate Valve effects physically at the Control Valve Assembly during any test when the vehicle is stationary. (All of these solenoid valve operations can be observed in real time on Techstream -- SLFL, SLRL, SLFG, SLRG and SLAC where "L" = Levelling; "G" = Gate; AC = Accumulator -- but this is of little help when searching for leaks).

However, the pressures in the side-to-side connections between Right and Left as governed by the ECU and the Front and Rear Gate Valves respectively, are equal when the Gate Valves are open. These pressures would be expected to be the same as the respective Front and Rear line pressures elsewhere in the AHC system in this situation. (Note: There is no hydraulic connection between Front and Rear – the Front and Rear hydraulic circuits are separate in the two-channel AHC system on LC100/LX470).

The last page of the reference document (labelled Page 214) shows what is happening when the vehicle is at rest and being lowered. In this case the system is dropping from high pressure to low pressure. The Front and Rear Levelling Valves open until the selected height setting is reached and recognised by the ECU using inputs from the Height Control Sensors. The Height Control Accumulator solenoid valve is not open in this condition and the Height Control Accumulator is not active. The AHC Pump also is inactive.

Hope the search for leaks and the solutions all go well!

 

[BOB F]

Wow. Thank you so much for taking the time to write this. I really need to get the car on a lift and properly go through this. I have a lift in my garage but it may be a challenge getting this car on it due to height issues.

 

[growe]

It also may help to go to this reference
https://lc100e.github.io/manual/ (LC100 Factory Service Manual)
Then follow index tabs starting at the top left of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control & Skyhook TEMS

Do you have an updated link for this resource? I'm trying to diagnose/understand the AHC system on my '98 LX and this sounds exactly what I'm looking for.
Link returns a 404 though

 

[IndroCruise]

Do you have an updated link for this resource? I'm trying to diagnose/understand the AHC system on my '98 LX and this sounds exactly what I'm looking for.
Link returns a 404 though

Yes -- the link has been updated today at Post #7 this thread (the originator removed the word "manual" from the link address). Thanks for the heads-up.

Try this:

LC100 Factory Service Manual

Landcruiser 100 Series Factory Workshop Manual

lc100e.github.io

Also, see below some notes which were prepared for others and which may be of assistance ....

The link is for a Toyota LC100 resource published by Toyota Motor Corporation but it applies also to much of the Lexus LX470 "below the skin" (excluding some of the accessories and related electrics and different body details).

The AHC/TEMS systems are the same for LX470 and LC100 (where fitted).

It is always a good idea to cross-level the Front of the vehicle using a tape-measure and the torsion bar adjusters with engine OFF before commencing other AHC/TEMS work. See first attachment. (Front cross-levelling is not done with Techstream and Height Control Sensor readings).

In addition, it is helpful to check first the condition of the 'globes' as a whole -- this gives a base-line for later comparisons. See second attachment.

The indexing of the linked site is a bit clunky and difficult to search -- but it does work:

An illustrated General Description of AHC and TEMS can be found by following the tabs mentioned within the link below. This 20 page item is well-illustrated with diagrams and explanations of the function of each of the components in the AHC/TEMS system. It is good basic pre-reading and helps give a ‘mental picture’ of how these systems work. There is no diagnostic nor repair information in this section.

As a starting point, go to:
LC100 Workshop Manual - https://lc100e.github.io/
then use tabs at LHS of opening page
+ New Car Features
+ CHASSIS
+ Suspension
+ Active Height Control Suspension and Skyhook TEMS

Moving beyond the General Description .....

AHC and TEMS Diagnostics information is found here -- but Techstream is necessary to go beyond physical symptoms:

Go to:
LC100 Workshop Manual - https://lc100e.github.io/
then use tabs at LHS of opening page
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS

Repair and Specification Details are found here:

Go to:
LC100 Workshop Manual - https://lc100e.github.io/
then use tabs at LHS of opening page
+ Repair Manual
+ SUSPENSION AND AXLE
This section covers all non-AHC mechanical aspects of the suspension and axle arrangements.

Scrolling down further within this SUSPENSION AND AXLE section reveals the AHC repair and specification information:

+ ACTIVE HEIGHT CONTROL SYSTEM (Independent Front Suspension)
+ ACTIVE HEIGHT CONTROL PUMP & MOTOR (Independent Front Suspension)
+ CONTROL VALVE ASSEMBLY (Independent Front Suspension)
+ HEIGHT CONTROL ACCUMULATOR (Independent Front Suspension)
+ PUMP ATTENUATOR (Independent Front Suspension)
+ DAMPING FORCE CONTROL ACTUATOR (Independent Front Suspension)
+ HEIGHT CONTROL SENSOR (Independent Front Suspension)

The following IH8MUD links are worthwhile starting points on AHC/TEMS matters:

https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520
This is a long thread but just start at the beginning and continue until it becomes a bit repetitive. Along the way at Post #5 in this thread, see the excellent video and "cheat sheet" about adjusting AHC pressures -- prepared and published by @suprarx7nut .

Front AHC pressures usually can be managed with the torsion bar adjusters -- but cross-level first per the first attachment.

Unlike a conventional suspension, the torsion bar adjusters have just two purposes on an AHC-equipped vehicle:

1. cross-levelling the Front of the vehicle, meaning equalising the hub-to-fender heights using tape measure, not Techstream -- this is an essential first step to check that the loads on each torsion bar are balanced before doing any AHC adjustments and 'fine tuning', and,

2. adjusting load share between Front torsion bars and Front AHC system (unlike a conventional suspension the so-called 'shock absorbers' are merely hydraulic struts used to carry part of the mass of the vehicle, and, enable ride height variation using the console switch, and, provide continuous auto self-levelling in real time (Active Height Control = AHC) in conjunction with the Height Control Sensors, the Control Valve Assembly, the AHC Pump and the Electronic Control Unit,

'Ride Height' is set at "N" height using the adjusters at the Height Control Sensors (not the torsion bar adjusters).

There is no easy provision for adjusting Rear AHC pressures -- usually it boils down to adding spacers or using springs with a higher spring rate. Australian-made KING KTRS-79 work well at the Rear. Some folks add or substitute airbags inside the rear coils. Others with VERY heavy vehicles or loads have used standard (non-AHC) Land Cruiser Rear coils. The airbags provide a flexible approach for different load conditions but may be over-kill if used in addition to higher spring rate springs. Gross Vehicle Mass (GVM) or Gross Vehicle Weight Rating (GVWR) may need to be monitored along with axle loadings -- policing of vehicle weights and loadings is enforced more strictly in some jurisdictions than others.

Note that an increased 'ride height' of the vehicle can be set at "N" height using the Height Control Sensor adjusters (the so-called "Sensor Lift") but this will mean that springs and torsion bars then are extended and will carry less weight, so the AHC system carries more weight, meaning that AHC pressures increase and must be compensated to bring them back within the FSM-specified range.

A good wiring diagram can be found here -- it is for LX470 and there will be some differences due to accessories, different engines, different models and years, LHD versus RHD -- but it is handy for AHC/TEMS purposes:
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

A few more useful links:

Parts Catalogue -- good to identify Part Numbers -- use own VIN at:

Parts catalog for Toyota Land Cruiser - https://toyota-general.epc-data.com/land_cruiser/

Harness and Connectors
https://www.toyota-tech.eu/wire_harness_rm/RM06H0E.pdf

That should be enough to get started. Hope all goes well!!

 

[growe]

Yes -- the link has been updated today at Post #7 this thread (the originator removed the word "manual" from the link address). Thanks for the heads-up.

Try this:

LC100 Factory Service Manual

Landcruiser 100 Series Factory Workshop Manual

lc100e.github.io

Also, see below some notes which were prepared for others and which may be of assistance ....

The link is for a Toyota LC100 resource published by Toyota Motor Corporation but it applies also to much of the Lexus LX470 "below the skin" (excluding some of the accessories and related electrics and different body details).

The AHC/TEMS systems are the same for LX470 and LC100 (where fitted).

It is always a good idea to cross-level the Front of the vehicle using a tape-measure and the torsion bar adjusters with engine OFF before commencing other AHC/TEMS work. See first attachment. (Front cross-levelling is not done with Techstream and Height Control Sensor readings).

In addition, it is helpful to check first the condition of the 'globes' as a whole -- this gives a base-line for later comparisons. See second attachment.

The indexing of the linked site is a bit clunky and difficult to search -- but it does work:

An illustrated General Description of AHC and TEMS can be found by following the tabs mentioned within the link below. This 20 page item is well-illustrated with diagrams and explanations of the function of each of the components in the AHC/TEMS system. It is good basic pre-reading and helps give a ‘mental picture’ of how these systems work. There is no diagnostic nor repair information in this section.

As a starting point, go to:
LC100 Workshop Manual - https://lc100e.github.io/
then use tabs at LHS of opening page
+ New Car Features
+ CHASSIS
+ Suspension
+ Active Height Control Suspension and Skyhook TEMS

Moving beyond the General Description .....

AHC and TEMS Diagnostics information is found here -- but Techstream is necessary to go beyond physical symptoms:

Go to:
LC100 Workshop Manual - https://lc100e.github.io/
then use tabs at LHS of opening page
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS

Repair and Specification Details are found here:

Go to:
LC100 Workshop Manual - https://lc100e.github.io/
then use tabs at LHS of opening page
+ Repair Manual
+ SUSPENSION AND AXLE
This section covers all non-AHC mechanical aspects of the suspension and axle arrangements.

Scrolling down further within this SUSPENSION AND AXLE section reveals the AHC repair and specification information:

+ ACTIVE HEIGHT CONTROL SYSTEM (Independent Front Suspension)
+ ACTIVE HEIGHT CONTROL PUMP & MOTOR (Independent Front Suspension)
+ CONTROL VALVE ASSEMBLY (Independent Front Suspension)
+ HEIGHT CONTROL ACCUMULATOR (Independent Front Suspension)
+ PUMP ATTENUATOR (Independent Front Suspension)
+ DAMPING FORCE CONTROL ACTUATOR (Independent Front Suspension)
+ HEIGHT CONTROL SENSOR (Independent Front Suspension)

The following IH8MUD links are worthwhile starting points on AHC/TEMS matters:

https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520
This is a long thread but just start at the beginning and continue until it becomes a bit repetitive. Along the way at Post #5 in this thread, see the excellent video and "cheat sheet" about adjusting AHC pressures -- prepared and published by @suprarx7nut .

Front AHC pressures usually can be managed with the torsion bar adjusters -- but cross-level first per the first attachment. Unlike a conventional suspension, the torsion bar adjusters have just two purposes on an AHC-equipped vehicle:

1. cross-levelling the Front of the vehicle, meaning equalising the hub-to-fender heights using tape measure, not Techstream -- this is an essential first step when doing any AHC adjustments and 'fine tuning', and,

2. adjust load share between Front torsion bars and Front AHC system (unlike a conventional suspension the so-called 'shock absorbers' are merely hydraulic struts used to carry part of the mass of the vehicle, and, enable ride height adjustment in conjunction with the Height Control Sensors, the Control Valve Assembly, the AHC Pump and the Electronic Control Unit,

'Ride Height' is set at "N" height using the adjusters at the Height Control Sensors (not the torsion bar adjusters).

There is no easy provision for adjusting Rear AHC pressures -- usually it boils down to adding spacers or using springs with a higher spring rate. Australian-made KING KTRS-79 work well at the Rear. Some folks add or substitute airbags inside the rear coils. Others with VERY heavy vehicles or loads have used standard (non-AHC) Land Cruiser Rear coils. The airbags provide a flexible approach for different load conditions but may be over-kill if used in addition to higher spring rate springs. Gross Vehicle Mass (GVM) or Gross Vehicle Weight Rating (GVWR) may need to be monitored along with axle loadings -- policing of vehicle weights and loadings is enforced more strictly in some jurisdictions than others.

Note that an increased 'ride height' of the vehicle can be set at "N" height using the Height Control Sensor adjusters (the so-called "Sensor Lift") but this will mean that springs and torsion bars then are extended and will carry less weight, so the AHC system carries more weight, meaning that AHC pressures increase and must be compensated to bring them back within the FSM-specified range.

A good wiring diagram can be found here -- it is for LX470 and there will be some differences due to accessories, different engines, different models and years, LHD versus RHD -- but it is handy for AHC/TEMS purposes:
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

A few more useful links:

Parts Catalogue -- good to identify Part Numbers -- use own VIN at:

Parts catalog for Toyota Land Cruiser - https://toyota-general.epc-data.com/land_cruiser/

Harness and Connectors
https://www.toyota-tech.eu/wire_harness_rm/RM06H0E.pdf

That should be enough to get started. Hope all goes well!!

Wow, you're a saint. Thanks for such a detailed writeup.