Definitive list of AHC maintenance items (9 Viewers)

[IndroCruise]

Just to add ....

No fluid emerging from the bleeders means that the AHC system is not yet pressurised.

To pressurise the system, you will need to get the AHC Pump running to prime the system properly using the "ActiveTest" procedure as described previously. (I see that you have not yet opened the attachment sent previously??) When that is done, exit the "Active Test" procedure and allow the AHC system to run.

You have wondered about valves downstream from the Pump.

The Control Valve Assembly is located midway along the inner edge of the LHS chassis rail. This contains the Front Levelling Valve and the Rear Levelling Valve. When the vehicle is being raised (or lowered) these valves are opened by the Electronic Control Unit (ECU) but only when the system is not in 'fail safe' mode.

After the vehicle is raised, the AHC Pump re-pressurises the Height Control Accumulator.

While theae latter details are all very interesting, they are not relevant.

At the moment, the AHC system is in 'fail safe' mode and the ECU is not allowing anything to happen.

Manual operation using the "Active Test" procedure is your way to bypass this control and prime and re-pressurise the AHC system, then exit this procedure. The ECU will then allow the system to run again.

The problem and the resolution are not unusual.

Just to add a bit more to overcome possible confusion .....

There is no point in trying to prime the system by applying 12 volt power directly to the AHC Pump. This will achieve pretty close to nothing because the Front and Rear Levelling Valves are closed and preventing fluid flow at the moment. They will not be opened simply by providing 12 volt power to the pump. This why the "Active Test" procedure must be used -- because the procedure allows these valves to be opened if it is followed exactly as described. It is a standard Toyota/Lexus procedure which also is found in the Factory Service Manual.

Hoping to hear of your success ....

 

[Urtwob]

Just wondering whether you have Techstream running and if so, what Diagnostic Trouble Codes (DTC's) are appearing?

Unfortunately I don’t have any techstream

Just to add ....

No fluid emerging from the bleeders means that the AHC system is not yet pressurised.

To pressurise the system, you will need to get the AHC Pump running to prime the system properly using the "ActiveTest" procedure as described previously. (I see that you have not yet opened the attachment sent previously??) When that is done, exit the "Active Test" procedure and allow the AHC system to run.

You have wondered about valves downstream from the Pump.

The Control Valve Assembly is located midway along the inner edge of the LHS chassis rail. This contains the Front Levelling Valve and the Rear Levelling Valve. When the vehicle is being raised (or lowered) these valves are opened by the Electronic Control Unit (ECU) but only when the system is not in 'fail safe' mode.

After the vehicle is raised, the AHC Pump re-pressurises the Height Control Accumulator.

While theae latter details are all very interesting, they are not relevant.

At the moment, the AHC system is in 'fail safe' mode and the ECU is not allowing anything to happen.

Manual operation using the "Active Test" procedure is your way to bypass this control and prime and re-pressurise the AHC system, then exit this procedure. The ECU will then allow the system to run again.

The problem and the resolution are not unusual.

Hi Indrocruise.
I have got a little lost in my posts, on the forum, back on track now.

I have now caught up and thank you so much for all your guidance.
We are looking at your notes right now and preparing to follow through.

I had never heard of “fail-safe” mode.

You have no idea how relieved I am.
We are not out of the woods yet but we have hope now.

Apart from just wanting the car sorted, I have a very important drive to do tomorrow for an elderly gentleman who has found my truck to be absolutely crucial for taking him to critical medical appointments.
We have made a special ramp, combined with the truck sitting low, and the wide doors all come together to provide him with his only means to get mobile.

Unfortunately with the AHC not working he can still get into the vehicle but the “hardness” of ride is just not good for him.

So your inputs are not just extremely knowledgable but extremely important this evening.

We can keep working at it now.

Thank you.

 

[Urtwob]

Unfortunately I don’t have any techstream

Hi Indrocruise.
I have got a little lost in my posts, on the forum, back on track now.

I have now caught up and thank you so much for all your guidance.
We are looking at your notes right now and preparing to follow through.

I had never heard of “fail-safe” mode.

You have no idea how relieved I am.
We are not out of the woods yet but we have hope now.

Apart from just wanting the car sorted, I have a very important drive to do tomorrow for an elderly gentleman who has found my truck to be absolutely crucial for taking him to critical medical appointments.
We have made a special ramp, combined with the truck sitting low, and the wide doors all come together to provide him with his only means to get mobile.

Unfortunately with the AHC not working he can still get into the vehicle but the “hardness” of ride is just not good for him.

So your inputs are not just extremely knowledgable but extremely important this evening.

We can keep working at it now.

Thank you.

I meant to say we did checked rear axle height sensor as you suggested but it was still looking healthy my friend.

I believe you have us on the right track now with the “fail-safe mode”

 

[Urtwob]

Just wondering whether you have Techstream running and if so, what Diagnostic Trouble Codes (DTC's) are appearing?

Unfortunately I don’t have any techstream

Thank you guys I leant a lot from this thread.

How I have a question, how do you think about the spring spacers vs new OEM springs? I don't want to do heavy load on my LX just want to have the OEM performance.

Hi Sunfic.
I had this dilemma recently.
I ended up fitting non OEM springs but from a very reputable 4x4 supply company in England. They guaranteed the springs to be exactly same spec as the OEM springs.
When they came I found the springs to be made in Japan and I am very happy with them. They were only half the price of the OEM springs so I thought it better to use these than put in the spacers.
The company I refer to are an English Company call Milner’s Japanese 4x4 parts.
00 44 1629 734411.
I have had years of great service from these guys.
However I will put up a post to comment further after I have had time to drive and use them.
I will add, I do use a trailer a lot on my Jeep and I actually really need the AHC working for personal reasons, so I will test these new springs but I have a contingency plan to install an “Airlift” kit to support the suspension when using a trailer. I believe I can have a reliable kit installed for less than £150. Look up AirLift on Amazon.com.
I hope this helps my friend.

 

[sunfic]

Unfortunately I don’t have any techstream

Hi Sunfic.
I had this dilemma recently.
I ended up fitting non OEM springs but from a very reputable 4x4 supply company in England. They guaranteed the springs to be exactly same spec as the OEM springs.
When they came I found the springs to be made in Japan and I am very happy with them. They were only half the price of the OEM springs so I thought it better to use these than put in the spacers.
The company I refer to are an English Company call Milner’s Japanese 4x4 parts.
00 44 1629 734411.
I have had years of great service from these guys.
However I will put up a post to comment further after I have had time to drive and use them.
I will add, I do use a trailer a lot on my Jeep and I actually really need the AHC working for personal reasons, so I will test these new springs but I have a contingency plan to install an “Airlift” kit to support the suspension when using a trailer. I believe I can have a reliable kit installed for less than £150. Look up AirLift on Amazon.com.
I hope this helps my friend.

Thank you Urtwob,

The reason that I want to ask the question is that in US currently we have a promotion from the dealership for parts, I can get the rear springs around $90 each and I am thinking with the spacer price about $40 each, if it is only a temporary solution I would rather stock the OEM springs right now.

 

[2001LC]

We're having a problem in the USA with AHC fluid jelling. This has only been seen coming from the AHC fluid in the 1L plastic bottles (jelling). Toyota has now gone back to 2.5L metal containers (no jelling). Perhaps you've gotten some in you reservoir. Once into pump, it can't build pressure. Some have tried cleaning pump, to no avail. They've had to replace the pump. In some cases Toyota Dealership, paid for the pump. So make sure your fluid is good, and not jelled.

Bad height sensor(s) is also a very real possibility. The ball joints in arms are freezing. You riding on bump stopped may have bent the arm and or possible damaged the height sensor.

 

[Urtwob]

Just to add ....

No fluid emerging from the bleeders means that the AHC system is not yet pressurised.

To pressurise the system, you will need to get the AHC Pump running to prime the system properly using the "ActiveTest" procedure as described previously. (I see that you have not yet opened the attachment sent previously??) When that is done, exit the "Active Test" procedure and allow the AHC system to run.

You have wondered about valves downstream from the Pump.

The Control Valve Assembly is located midway along the inner edge of the LHS chassis rail. This contains the Front Levelling Valve and the Rear Levelling Valve. When the vehicle is being raised (or lowered) these valves are opened by the Electronic Control Unit (ECU) but only when the system is not in 'fail safe' mode.

After the vehicle is raised, the AHC Pump re-pressurises the Height Control Accumulator.

While theae latter details are all very interesting, they are not relevant.

At the moment, the AHC system is in 'fail safe' mode and the ECU is not allowing anything to happen.

Manual operation using the "Active Test" procedure is your way to bypass this control and prime and re-pressurise the AHC system, then exit this procedure. The ECU will then allow the system to run again.

The problem and the resolution are not unusual.

Hi Indrocruise,

Just a wee note to say how much I appreciate your determined efforts to understand and then offer guidance as to best way forward. All of your inputs today were top level and hopefully tomorrow I will be able to report a successful conclusion.

But for now, may I offer my deepest felt gratitude for all you help.

Thank you.

 

[IndroCruise]

Hi Indrocruise,

Just a wee note to say how much I appreciate your determined efforts to understand and then offer guidance as to best way forward. All of your inputs today were top level and hopefully tomorrow I will be able to report a successful conclusion.

But for now, may I offer my deepest felt gratitude for all you help.

Thank you.

Firstly, congratulations on changing out the rear shock absorbers and springs on a AHC-equipped vehicle. That is a major achievement!

Secondly, apologies offered for the somewhat incoherent sequence of my earlier posts – I should have recognised your vehicle’s symptoms more quickly. It was well after midnight in my part of the world (Brisbane Australia) and clearer thinking in the morning would have been better – but you appeared to be in immediate trouble.

The following notes attempt to put the story together.

Looking at your old posts, I gather that your vehicle is a 1998 Landcruiser Amazon HZJ100 – so 6 cylinder 4.2 litre diesel engine (corrected) with AHC, now about 24 years old. (By the way, it is a good idea to put the vehicle details in a signature line on your IH8MUD profile – this avoids a lot of guesswork for the reader).

You mentioned that “My rear lhs strut burst over a month ago”. Not sure whether that means they fell apart due to rust?

You also mention a few times that a heavy trailer often has been used with your vehicle. The weight of the trailer on the towball will increase the Rear AHC quite a lot and maybe that has weakened the seals inside the Shock Absorbers and eventually a major leak of AHC Fluid may have occurred? So not sure whether this is what is meant by “My rear lhs strut burst over a month ago”? If the vehicle drops to “LO” when it is loaded, or refuses to raise to “HI” when it is loaded, then that is a good indication that the AHC pressures are excessive – because that is what the system is designed to do when it is overloaded.

The "General Description" of the LC100/LX470 AHC/TEMS systems provides good general information on how these systems are meant to work and their limitations including load limitations. This short (20 page) document can be found here:

LC100 Factory Service Manual

Landcruiser 100 Series Factory Workshop Manual

lc100e.github.io

Follow the tabs on the opening panel on the left hand side of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control Suspension and Skyhook TEMS

This web reference also provides the complete Factory Service Manual (FSM) for your vehicle

For on-vehicle inspection and settings, look under
Repair Manual > SUSPENSION AND AXLE > Active Height Control System

For diagnostics, look under
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS

Moving on ....

You have advised that when 12 volts are applied directly to the AHC Pump on your vehicle, it delivers fluid on open circuit (when the AHC pipe is disconnected from the pump) but does not deliver fluid when the AHC pipe is reconnected. This means either

Alternative #1: There is air in the pump -- almost certain after disconnecting and reconnecting the AHC pipe, and, after changing out Shock Absorbers there is considerable air in the system anyway, even though this has been reduced by filling Shock Absorbers with AHC Fluid before installing them. If you had Techstream you would see Diagnostic Trouble Codes (DTC’s) 1751 and 1762 – but all that matters now is that you can see that the AHC Pump stops or won't operate, which is what the system and its ECU are designed to do in this circumstance. This is how the faults and the 'fail-safe function' are explained in the Factory Service Manual:

The extract immediately below shows how the pump bleed procedure is described in the Factory Service Manual. You will notice that it refers to the DLC3 Diagnostic socket which is found under the dashboard, depicts slightly different connections. As described and attached to my post #895 in this thread, I use and I recommend the version using the DLC1 Diagnostic socket in the engine bay. This comes from another version of the Factory Service Manual and was provided long ago by IH8MUD Member and AHC guru @PADDO. It is much more convenient and provides the same effect. I have shown the version below only for completeness.

Alternative #2: As reminded by @2001LC, there may be a blockage in the pump. If this happens, there may be fluid flow on open circuit (when the AHC pipe is disconnected from the pump) but the internal partial blockage inside the AHC Pump may mean that it builds up high internal pressure but the internal blockage prevents sufficient pressure being delivered to drive the AHC system. In this situation, Techstream would be expected to show DTC 1751 and DTC 1762 if the blockage causes the pump to be starved of AHC Fluid on the inlet side, or DTC 1763 if the blockage is on the outlet side and prevents the pump from delivering AHC Fluid. Again, in either case, the bottom line is that the pump stops or not will not operate. The problematic faulty AHC Fluid described as causing blockages in the US market has not been reported in the Australian market, where AHC Fluid always has been imported from Japan and supplied in 2.5 litre steel drums – Toyota/Lexus Part No. 08886-01805. I am unsure of AHC Fluid supply arrangements in the EU and UK markets – but it is best to be wary. Hopefully this not your problem as the fix is not easy, would require disassembly and cleaning of the tiny filter/strainers inside the AHC Pump, or more simply, replacement with a new AHC Pump!!

Separately, there can be a different problem .....

Alternative #3: As mentioned in my earlier posts and as reminded by @2001LC, damage to the Rear Height Control Sensor and/or its linkage, connector and harness, also may result in a ‘fail safe function’ which prohibits operation of the AHC system. If this happens, then the pump stops or does not operate – all due to damage either by these parts being “stretched” while changing springs, or, by being “buckled” by the vehicle riding on the bump-stops, and/or the sensor being damaged internally -- or simply an effect of old age and wear and tear. The Height Control Sensors are 'wear items' and some would say that 24 years is a 'fair innings'. Hopefully this not your problem as the fix most likely will require a new sensor and linkage!!

Control of the AHC and TEMS systems rests with the AHC Electronic Control Unit (ECU). The ECU resides deep under the dashboard and is connected to the various components and sensors in the system by an elaborate wiring harness and connectors. By modern standards, this +25 year old technology is quite ancient – but it still works very effectively if the components are healthy and not rusted out nor physically damaged.

The purpose of each of the various 'fail-safe functions' mentioned in FSM extracts above is to prevent that part of the system from destroying itself during a malfunction, or to prevent the vehicle becoming unsafe in some way. The 'fail-safe' mode prevails until it is cleared. If it is cleared but the fault remains, then that 'fail-safe mode' will return immediately -- and will reappear as a DTC if Techstream or other relevant scanner is used.

Other problems beyond the above alternatives are possible but seem less likely. For example, problems with the Control Valve Assembly or its connector or harness are possible but seem to be very rare. The Control Valve Assembly is located on the inner side of the Left Hand Side chassis rail. It is worthwhile to make sure that its connector has a suitable shroud where the wiring passes from the harness into the connector and that is well protected from debris, salt, or whatever is thrown up from the road while travelling.

The Control Valve Assembly contains the Front Levelling Valve and the Rear Levelling Valve (and also the Gate Valves but these are not relevant to the current discussion). The Levelling Valves remain closed at all times unless directed to open by the ECU (or unless there is a faulty valve). The Levelling Valves also hold the fluid in place (provided the valves are healthy) and this is why the vehicle does not sink when parked. It is also why you could not achieve flow in the AHC system when operating the AHC Pump with a direct 12 volt supply on to the motor terminals – because the Levelling Valves remain closed and AHC Fluid cannot flow past them to ‘globes’ and Shock Absorbers. The electrical ‘bypass’ provided by the “Active Test” procedure is necessary.

Hope this helps!!

 

[Urtwob]

Firstly, congratulations on changing out the rear shock absorbers and springs on a AHC-equipped vehicle. That is a major achievement!

Secondly, apologies offered for the somewhat incoherent sequence of my earlier posts – I should have recognised your vehicle’s symptoms more quickly. It was well after midnight in my part of the world (Brisbane Australia) and clearer thinking in the morning would have been better – but you appeared to be in immediate trouble.

The following notes attempt to put the story together.

Looking at your old posts, I gather that your vehicle is a 1998 Landcruiser Amazon 100 HJZ – so V8 2UZ-FE petrol engine with AHC, now about 24 years old. (By the way, it is a good idea to put the vehicle details in a signature line on your IH8MUD profile – this avoids a lot of guesswork for the reader).

You mentioned that “My rear lhs strut burst over a month ago”. Not sure whether that means they fell apart due to rust?

You also mention a few times that a heavy trailer often has been used with your vehicle. The weight of the trailer on the towball will increase the Rear AHC quite a lot and maybe that has weakened the seals inside the Shock Absorbers and eventually a major leak of AHC Fluid may have occurred? So not sure whether this is what is meant by “My rear lhs strut burst over a month ago”? If the vehicle drops to “LO” when it is loaded, or refuses to raise to “HI” when it is loaded, then that is a good indication that the AHC pressures are excessive – because that is what the system is designed to do when it is overloaded.

The "General Description" of the LC100/LX470 AHC/TEMS systems provides good general information on how these systems are meant to work and their limitations including load limitations. This short (20 page) document can be found here:

LC100 Factory Service Manual

Landcruiser 100 Series Factory Workshop Manual

lc100e.github.io

Follow the tabs on the opening panel on the left hand side of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control Suspension and Skyhook TEMS

This web reference also provides the complete Factory Service Manual (FSM) for your vehicle

For on-vehicle inspection and settings, look under
Repair Manual > SUSPENSION AND AXLE > Active Height Control System

For diagnostics, look under
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS

Moving on ....

You have advised that when 12 volts are applied directly to the AHC Pump on your vehicle, it delivers fluid on open circuit (when the AHC pipe is disconnected from the pump) but does not deliver fluid when the AHC pipe is reconnected. This means either

Alternative #1: There is air in the pump -- almost certain after disconnecting and reconnecting the AHC pipe, and, after changing out Shock Absorbers there is considerable air in the system anyway, even though this has been reduced by filling Shock Absorbers with AHC Fluid before installing them. If you had Techstream you would see Diagnostic Trouble Codes (DTC’s) 1751 and 1762 – but all that matters now is that you can see that the AHC Pump stops or not won't operate, which is what the system and its ECU are designed to do in this circumstance. This is how the faults and the 'fail-safe function' are explained in the Factory Service Manual:

View attachment 2961081

View attachment 2961082
This how the bleed procedure is described in the Factory Service Manual. You will notice that it refers to the DLC3 Diagnostic socket which is found under the dashboard, with slightly different connections. As described and attached to my post #895 in this thread, I use, and recommend the version using the DLC1 Diagnostic socket in the engine bay. This comes from another version of the Factory Service Manual and was provided long ago by AHC guru @PADDO. It is much more convenient and provides the same effect. I have shown the version below only for completeness.

View attachment 2961088


Alternative #2: As reminded by @2001LC, there may be a blockage in the pump. if this happens, there may be fluid flow on open circuit (when the AHC pipe is disconnected from the pump) but the internal partial blockage inside the AHC Pump means that it builds up high internal pressure but the internal blockage prevents sufficient pressure being delivered to drive the AHC system. In this situation, Techstream would be expected to show DTC 1763. Again, the bottom line is that the pump stops or not will not operate. The problematic faulty AHC Fluid described as causing blockages in the US market has not been reported in the Australian market, where AHC Fluid always has been imported from Japan and supplied in 2.5 litre steel drums – Toyota/Lexus Part No. 08886-01805. I am unsure of AHC Fluid supply arrangements in the EU and UK markets – but it is best to be wary. Hopefully this not your problem as the fix is not easy, would require disassembly and cleaning in the tiny filter/strainers inside the AHC Pump, or more simply, a new AHC Pump!!

View attachment 2961100
Separately, there can be a different problem .....

Alternative #3: As mentioned in my earlier posts and as reminded by @2001LC, damage to the Rear Height Control Sensor and/or linkage, connector or harness, also can result in a ‘fail safe function’ which prohibits operation of the AHC system. Then the pump stops or does not operate – all due to damage either by these parts being “stretched” while changing springs, or, by being “buckled” by the vehicle riding on the bump-stops, and/or the sensor being damaged internally. Hopefully this not your problem as the fix most likely will require a new sensor and linkage!!

View attachment 2961103

Control of the AHC and TEMS systems rests with the AHC Electronic Control Unit (ECU). The ECU resides deep under the dashboard and is connected to the various components and sensors in the system by an elaborate wiring harness and connectors. By modern standards, this +25 year old technology is quite ancient – but it still works very effectively if the components are healthy and not rusted out nor physically damaged.

Other problems beyond the above alternatives are possible but seem less likely. For example, problems with the Control Valve Assembly or its connector or harness are possible but seem to be very rare. The Control Valve Assembly is located on the inner side of the Left Hand Side chassis rail. It is worthwhile to make sure that its connector has a suitable shroud and is well protected from debris thrown up from the road while travelling.

The Control Valve Assembly contains the Front Levelling Valve and the Rear Levelling Valve (and also the Gate Valves but these are not relevant to the current discussion). The Levelling Valves remain closed at all times unless directed to open by the ECU (or unless there is a faulty valve). The Levelling Valves also hold the fluid in place (provided the valves are healthy) and this is why the vehicle does not sink when parked. It is also why you could not achieve flow in the AHC system when operating the AHC Pump with a direct 12 volt supply – because the Levelling Valves remain closed and AHC Fluid cannot flow past them to ‘globes’ and Shock Absorbers. The electrical ‘bypass’ provided by the “Active Test” procedure is necessary.

Hope this helps!!

Indrocruise, you are a true Super Star.

You may have no idea how much you have helped me, and yes you were correct to pick up that I had a relatively urgent situation.
It is concerning an elderly gentleman who has medical appointments to attend and who cannot do so unless the LC100 is available. I have used this vehicle for many such like activities.

So I am eternally grateful my friend.

By the way, I am writing from my home in a small town called Ballycastle up on the North Antrim Coast of Northern Ireland.
We look across the see to the Famous
“Mull of Kintyre” where Paul Mc Cartney of The Beatles sat on the Mull of Kintyre on his farm on the Scottish coast. It is only 25 miles across the Irish Sea. We can see it clearly from our farm on certain days.

Perhaps you may of heard of “The Giants Causeway”. It is a world famous landmark that is only 12 miles from my home.

I look forward to going back over your last reply. You have presented me with the most comprehensive library of information and guidance.

I agree with your comments re the rear height sensor. We did give it a visual inspection.

If the “Active Test” does not solve our problem in the morning, I will remove that height sensor and inspect it a bit more closely. They are relatively easy to disassemble and doing so will expose if “over-stretching” has indeed occurred.

I will keep you updated my friend.
But for now a little “shut-eye” is needed. It is 3.10am here in Ireland.

That said, I probably won’t go to sleep yet as I’m very very curious to look through all of your last post.

I feel privileged to have made your acquaintance on this brilliant forum.
Thank you

URTWOB.

 

[Urtwob]

Indrocruise, you are a true Super Star.

You may have no idea how much you have helped me, and yes you were correct to pick up that I had a relatively urgent situation.
It is concerning an elderly gentleman who has medical appointments to attend and who cannot do so unless the LC100 is available. I have used this vehicle for many such like activities.

So I am eternally grateful my friend.

By the way, I am writing from my home in a small town called Ballycastle up on the North Antrim Coast of Northern Ireland.
We look across the see to the Famous
“Mull of Kintyre” where Paul Mc Cartney of The Beatles sat on the Mull of Kintyre on his farm on the Scottish coast. It is only 25 miles across the Irish Sea. We can see it clearly from our farm on certain days.

Perhaps you may of heard of “The Giants Causeway”. It is a world famous landmark that is only 12 miles from my home.

I look forward to going back over your last reply. You have presented me with the most comprehensive library of information and guidance.

I agree with your comments re the rear height sensor. We did give it a visual inspection.

If the “Active Test” does not solve our problem in the morning, I will remove that height sensor and inspect it a bit more closely. They are relatively easy to disassemble and doing so will expose if “over-stretching” has indeed occurred.

I will keep you updated my friend.
But for now a little “shut-eye” is needed. It is 3.10am here in Ireland.

That said, I probably won’t go to sleep yet as I’m very very curious to look through all of your last post.

I feel privileged to have made your acquaintance on this brilliant forum.
Thank you

URTWOB.

Meant to say, all details correct except it is a 4.2 diesel truck, and I should of said the AHC strut burst due to rusting through.

 

[IndroCruise]

Meant to say, all details correct except it is a 4.2 diesel truck, and I should of said the AHC strut burst due to rusting through.

No problem @Urtwob -- post #908 has been amended. I also improved the explanation in "Alternative 2" as there are two filters/strainers inside the AHC Pump -- one on the inlet side of the pump and one on the discharge side.

 

[Urtwob]

No problem @Urtwob -- post #908 has been amended. I also improved the explanation in "Alternative 2" as there are two filters/strainers inside the AHC Pump -- one on the inlet side of the pump and one on the discharge side.

Good afternoon Indrocruise;
Unfortunately we have not been able to get the “Active Test” to work.

I insert the wire bridge
Select “Comfort”
Turn on Engine and
Within 5 seconds press the “down” button 5 times and then hold down for 5 seconds. Then press “Up”.

We have tried this equence a number of times.
There is no array of flashing lights in the instrument panel.
And the AHC pump has not ever come on.

Then I tried putting the wire link into the OBD plug inside the Jeep but could not get it to operate for us.
We can’t get to the point of having all the internal control lights flashing as it is described in the PDF.

 

[Urtwob]

At

No problem @Urtwob -- post #908 has been amended. I also improved the explanation in "Alternative 2" as there are two filters/strainers inside the AHC Pump -- one on the inlet side of the pump and one on the discharge side.

No problem @Urtwob -- post #908 has been amended. I also improved the explanation in "Alternative 2" as there are two filters/strainers inside the AHC Pump -- one on the inlet side of the pump and one on the discharge side.

Deeply grateful for your continued determination to help me.

Unfortunately we have not yet been able to get the truck to by-pass the ECU.
I HAVE tried the sequence many many times. At no point have we managed to get all the instrument cluster lights to start blinking.
The only light blinking is the AHC OFF light.

We have tried to use the onboard diagnostic plug inside the Jeep as well but it is just the same. Result.
So as yet we haven’t been able to get any of the UP OR FOWN buttons to work on any manner.

 

[IndroCruise]

At


Deeply grateful for your continued determination to help me.

Unfortunately we have not yet been able to get the truck to by-pass the ECU.
I HAVE tried the sequence many many times. At no point have we managed to get all the instrument cluster lights to start blinking.
The only light blinking is the AHC OFF light.

We have tried to use the onboard diagnostic plug inside the Jeep as well but it is just the same. Result.
So as yet we haven’t been able to get any of the UP OR FOWN buttons to work on any manner.

Mmmm – this is a disappointing result and it suggests that it is time to look for deeper causes of AHC non-operation beyond the basic hydraulic issues.

I think you have followed the “Active Test” procedure – but here it is again expressed in different words from one of my other posts, just in case it helps ….

Put the bridge in place between E1 and Ts terminal with ignition "OFF", then sit in the car, start engine and immediately hold down the "DOWN" rocker switch for at least 5 seconds. This puts the system into test mode and a lot of warning lights blink in the instrument cluster because various systems have been by-passed. Now you are in test mode, follow the instructions in the box to move the Front or Rear up or down.

We are particularly interested in the following, with the engine still running:

• for the Front when in Active Test mode, put the console switch into "Comfort" position, AND then press the "UP" rocker switch, and separately,
• for the Rear when in Active Test mode, put the console switch into the "Comfort" position, AND hold down the "ON/OFF" switch, AND at the same time, press the "UP" rocker switch.

In both cases, don't go too far -- do not want to push against the upper limits of the suspension travel, which is why the warning is given in the notes. If it seems to get out of hand or you become uncomfortable, press the "DOWN" rocker switch, or, turn the engine "OFF" and start again.

The main purposes here are to see whether these steps do start the Pump -- which should happen -- and that the relevant Levelling Valve in the Control Valve Assembly does open -- and whether the vehicle does actually rise as it should.

If there is no response to the "UP" movement in this "Active Test", then a relay or fuse somewhere in the AHC system is not allowing power to arrive via the AHC system to the motor driving the Pump.

The next steps will be to find the cause.

You have shown previously that the Pump and its motor are capable of operating when connected directly to the battery.

In normal operation, voltage will be seen at the AHC Pump only when the ECU is telling the Pump to run AND when all electrical apparatus is functional and allowing power to arrive at the Motor under the control of the AHC system

At the moment, it is unclear whether that signal is being sent by the ECU to the Pump due to a problem elsewhere causing a fault or a conflict – but you know that the motor driving the AHC Pump is healthy, meaning that it can run when directly connected to a 12 volt source.

With the engine running, for completeness check the voltage at the plug which connects to the electric motor – it is expected to be zero given the circumstances but if ~12 volts is seen at this plug, that would indicate a connector problem, given that the motor is known to operate if it receives voltage.

In the case of no voltage arriving at the motor driving the AHC Pump, the electrical system will have to be explored, starting with easy basic things first. My suggestions are as follows:

1. Disconnect the battery in the car and leave it disconnected for a few minutes. This has the effect of “powering down” all the systems in the vehicle – somewhat like rebooting a laptop or a phone -- and also should clear any fault conditions stored in various places. Faults that still exist won’t go away and will return as soon power is reconnected but at least any irrelevant legacy issues will be cleared. Reconnect the battery.

2. Check that the battery is healthy.

3. Now commence checking all AHC-related fuses and relays. The locations of these things varies somewhat with different models and model years and Right Hand Drive versus Left Hand Drive. My 2006 Right Hand Drive LC100 is on the other side of Australia so I am trying to remember location details without being able to check – in any case, your 1998 Right Hand Drive LC100 may be different and both will have some layout differences compared to Left Hand Drive vehicles. Better information may be found here:

LC100 Workshop Manual - https://lc100e.github.io/
Look down the list for “Electrical Wiring Diagram” and explore the various sub-headings, looking for your model year and RHD versus LHD. This source provides various layout diagrams as well as the Electrical Wiring Diagrams (EWD's).

4. Look for the Fuse Box in the engine bay -- Toyota calls these things Junction Boxes (J/B) -- and check all fuses and relays that are marked “AHC”.

5. As well as fuses and relays in the engine bay, also check fuses in behind the covers in the front footwells. One of these fuses is the “AHC-IG Fuse”. The pic below gives the idea showing Left front footwell – but I am not sure whether this is Left Hand Drive pic or Right Hand Drive pic or which model year. The relevant location may (?) be on the right hand side in your vehicle.

6. Also check the “AHC-B Fuse” – this is a pic in the left footwell of a Left Hand Drive vehicle and you may have to look on the other side.

7. If all the fuses are good, and with the battery reconnected, suggest another quick check of whether the “Active Test” produces any movement. If so, raise vehicle sufficiently (without over-raising) to prime AHC Pump and AHC system, then exit “Active Test” and check whether AHC works as it should,

8. If no success, then it is time to suspect a fault in the AHC Main Relay. If this relay is faulty, then no power can arrive at the AHC system and nothing can happen other than a flashing green “OFF” light. There is a test procedure in the Factory Service Manual -- LC100 Workshop Manual - https://lc100e.github.io/ look under Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION > C1783 -- but simply purchasing and replacing the AHC Main Relay may be the expedient step.

The example layout below comes from another model -- more relevant details should be explored in
LC100 Workshop Manual - https://lc100e.github.io/ -- look down the list for “Electrical Wiring Diagram” and then within the sub-lists for correct RHD model year.

If purchasing a replacement AHC Main Relay, then it is very important to acquire the RHD version and not the LHD version.

9. If it is necessary to go beyond the AHC Main Relay, it will be necessary to did even deeper, probably including checking the condition and function of the AHC Electronic Control Unit (ECU) itself.

10. Meanwhile, even though it seems trite, in a 24 years old vehicle it is also worth checking the actual condition of the console switch even though there are no DTC indicators -- test details are found in FSM Diagnostics at C1786, C1787, C1788 -- also see pics at Suspension problem even after replacing almost everything - https://forum.ih8mud.com/threads/suspension-problem-even-after-replacing-almost-everything.812905/page-2#post-9444084 . The console switch can be subject to spills of water, coffee, etc. If this has happened, there will be corrosion or mess on the switch contacts. It is not difficult to pull the switch assembly and clean.

The situation is becoming more challenging -- but still hoping for success!!

 

[IndroCruise]

Just had another look through the earlier posts ....

Back at a Post #894 you mentioned:

"When we start truck and hold hand on AHC pump we can feel a small clunk and on goes the AHC off light inside the truck".

Did this also happen when you were doing the "Active Test"?

The point is whether this demonstrates that power actually IS arriving at the AHC Pump motor?

If so, pump blockage may be the problem.

I am concerned that I may have jumped to a conclusion. When the "Active Test" is performed correctly and there is no movement, it means no power is arriving at the AHC Pump.

Perhaps you could comment on whether you observed power arriving at the AHC Pump?? If so, Pump blockage must be considered seriously per "Alternative #2" in my earlier post.

 

[Urtwob]

Just had another look through the earlier posts ....

Back at a Post #894 you mentioned:

"When we start truck and hold hand on AHC pump we can feel a small clunk and on goes the AHC off light inside the truck".

Did this also happen when you were doing the "Active Test"?

The point is whether this demonstrates that power actually IS arriving at the AHC Pump motor?

If so, pump blockage may be the problem.

I am concerned that I may have jumped to a conclusion. When the "Active Test" is performed correctly and there is no movement, it means no power is arriving at the AHC Pump.

Perhaps you could comment on whether you observed power arriving at the AHC Pump?? If so, Pump blockage must be considered seriously per "Alternative #2" in my earlier post.

Once again, a dedicated approach and response. A million “Thank-you’s” my friend.
It is 3am in Ireland just now. I will get back to the Lady in the morning.

Just for clarity,
When I go through the “Active Test” process, the Off indicator light of the AHC on/Off switch, does Flash. However no other lights of any kind Starr to flash in the main console or the climate console. Everything stays just as was.

Further,
Now I know this may be irrelevant but without going into Active Test, when you switch on engine the orange coloured AHC Off light is flashing. The Green Low light is glowing steady.
If you press the “Up” button the AJC status light will step up through “N” and up to “Hi”
The AHV status array will now have a Solid green “Lo” light and a flashing “Hi” light on display. But no response with AHC motor etc.

Taking this further, we then put a Jack under the vehicle and raised the vehicle up.

After doing so, the AHC status lights behaviour changed.
The solid “Lo” geeen light stayed on but when pressing the Up button we could not get the status light to step up to either N or Hi.
We repeated this action both in front and rear of vehicle.

It was a crude exercise but I did it in an attempt to see if moving the AHC height sensor apparatus switches on the rear axle or the front two sensors on either the LHS or RHS front wheels, had any effect in the AHC status indicators.

There was an effect noted.

When car was jacked up either front or rear we could not get the green AHC status indicator light to step up through to “N” or “Hi”.
The objective was to determine if moving any one of the 3 remote AHC movement sensors, had a corresponding response in the AHC status indicator. And yes indeed by moving these movement sensors individually the AHC status indicator panel behaved differently.

This was my “crude” attempt to check if the remote sensors were still being “seen” by the ECU.
In my crude test it appears by moving the remote sensors we did elicit a corresponding response in the AHC status panel this potentially illustrating that the remote AHC sensors are working and sending signal to the AHC ECU.
Therefore I am relatively confident the remote sensors are still healthy and potentially showing they are not damaged by over stretching of other potential sensor damage.

In the morning I will go through inspection of all related or relevant AHC fuses and the main AHC relay.

Thank you kind Sir.

 

[2001LC]

Take a step back!

Assuming AHC system was working okay before any work recently done. It would indicated some work done caused current issue.

1) When replacing rear springs. It's important that we do not stretch (pull on) rear height sensor. With LH shock disconnect, LH axle can be lower further than sensor swing arm can extend. If sensors arm gets pull down past it swing arm limit. We pull senor arm out of adjustment and or damage sensor.

So first think about how you replaced shock and or springs. Where you careful to not stretch rear sensor arm?
YES! Than sensor likely okay if it was okay before you started any work on springs & shocks.
NO! Than likely sensor out of adjustment, arm bent and or sensor damaged.

2) Replace shocks (hydraulic rams). There are two part seal at top of each shock, in the housing of high pressure hydraulic line that attach to the shock. If replaced, both must be install in correct order.
Did you replace seal, YES? In correct order, YES. Any leaks, NO. All good!
If seal not installed correctly or leaks. Correct.

3) Are any of the ball joints of arms of the 3 height sensor frozen?
NO! Good.
YES! that sensor may be damaged.

4) Is the vehicle a rust bucket?
Yes! Very likely a high pressure hard line is leaking. Replace any leaky lines.

This may be where you'd like to start. I say this because at some point, you said something about fluid in reservoir not dropping. If pump is running, fluid should drop lower in reservoir. If pump keeps running, fluid not dropping and vehicle not raising. This indicates pump is clogged or bad.
5) Was new bottle(s) of AHC fluid added?
YES! Remove fluid with a large hose and suction devise. Look for foreign materiel in fluid. Note: Large hose and suction devise, is used. So if a jell or other foreign matter in fluid, it will pass easily through it. So fluid can then be inspected. Point of this, is to get and idea is any thing may be clogging pump.

6) Is AHC reservoir very stained. Staining indicates old fluid was in the system a long time. Very old fluid will builds up solid matter. This matter may have dislodged from reservoir and clogged pump, during flushing procedure. Remove reservoir and pump. Clean or replace.

Once all good. Move rear senor arm in lowest position. This is put more weight on coil spring and less on AHC. See how AHC system behaves.
Then turn torsion bar adjusters, 5 clockwise turns each. This put more weight on torsion bars and less on AHC. See how AHC system behaves.


Good luck!

 

[Urtwob]

Take a step back!

Assuming AHC system was working okay before any work recently done. It would indicated some work done caused current issue.

1) When replacing rear springs. It's important that we do not stretch (pull on) rear height sensor. With LH shock disconnect, LH axle can be lower further than sensor swing arm can extend. If sensors arm gets pull down past it swing arm limit. We pull senor arm out of adjustment and or damage sensor.

So first think about how you replaced shock and or springs. Where you careful to not stretch rear sensor arm?
YES! Than sensor likely okay if it was okay before you started any work on springs & shocks.
NO! Than likely sensor out of adjustment, arm bent and or sensor damaged.

2) Replace shocks (hydraulic rams). There are two part seal at top of each shock, in the housing of high pressure hydraulic line that attach to the shock. If replaced, both must be install in correct order.
Did you replace seal, YES? In correct order, YES. Any leaks, NO. All good!
If seal not installed correctly or leaks. Correct.

3) Are any of the ball joints of arms of the 3 height sensor frozen?
NO! Good.
YES! that sensor may be damaged.

4) Is the vehicle a rust bucket?
Yes! Very likely a high pressure hard line is leaking. Replace any leaky lines.

This may be where you'd like to start. I say this because at some point, you said something about fluid in reservoir not dropping. If pump is running, fluid should drop lower in reservoir. If pump keeps running, fluid not dropping and vehicle not raising. This indicates pump is clogged or bad.
5) Was new bottle(s) of AHC fluid added?
YES! Remove fluid with a large hose and suction devise. Look for foreign materiel in fluid. Note: Large hose and suction devise, is used. So if a jell or other foreign matter in fluid, it will pass easily through it. So fluid can then be inspected. Point of this, is to get and idea is any thing may be clogging pump.

6) Is AHC reservoir very stained. Staining indicates old fluid was in the system a long time. Very old fluid will builds up solid matter. This matter may have dislodged from reservoir and clogged pump, during flushing procedure. Remove reservoir and pump. Clean or replace.

Once all good. Move rear senor arm in lowest position. This is put more weight on coil spring and less on AHC. See how AHC system behaves.
Then turn torsion bar adjusters, 5 clockwise turns each. This put more weight on torsion bars and less on AHC. See how AHC system behaves.


Good luck!

Thank you LC100

You have made a few very relevant points and I will go through them one by one in an effort to eliminate each “risk-area”.

I replaced the pipes from rear globes to the top of the struts a few month ago. We installed new seals at this time. I didn’t change them this time when installing new struts.

Also we had put in New AHC fluid at that time as well so the most recent AHC fluid was only a few months old.

My colleague took the old struts out and put the new ones in, I am not sure if he “tied up” the rear axle to prevent problem.

I will report back soon.

Thank you for your help and guidance.
This is indeed a fantastic forum and resource for all its members.

 

[Urtwob]

Thank you LC100

You have made a few very relevant points and I will go through them one by one in an effort to eliminate each “risk-area”.

I replaced the pipes from rear globes to the top of the struts a few month ago. We installed new seals at this time. I didn’t change them this time when installing new struts.

Also we had put in New AHC fluid at that time as well so the most recent AHC fluid was only a few months old.

My colleague took the old struts out and put the new ones in, I am not sure if he “tied up” the rear axle to prevent problem.

I will report back soon.

Thank you for your help and guidance.
This is indeed a fantastic forum and resource for all its members.

Apologies my last response was meant for 2001LC.
Thank you.

 

[2001LC]

Thank you LC100

You have made a few very relevant points and I will go through them one by one in an effort to eliminate each “risk-area”.

I replaced the pipes from rear globes to the top of the struts a few month ago. We installed new seals at this time. I didn’t change them this time when installing new struts.

Also we had put in New AHC fluid at that time as well so the most recent AHC fluid was only a few months old.

My colleague took the old struts out and put the new ones in, I am not sure if he “tied up” the rear axle to prevent problem.

I will report back soon.

Thank you for your help and guidance.
This is indeed a fantastic forum and resource for all its members.

"Also we had put in New AHC fluid at that time as well so the most recent AHC fluid was only a few months old."
So I understand this to mean: Had some AHC fluid leftover unused in a bottle, used when installed shocks. That AHC system worked okay last few months, with this few month old fluid. I recall also you had primed the new shock (likely, seen any jell in fluid). So not likely any jell in fluid!