AHC – so slow, erratic, what to do next? Help requested please (1 Viewer)

Joined
Dec 6, 2016
Messages
249
Location
Brisbane, Australia
Hi All,

Firstly, apologies in advance for this long post. It attempts to describe a current issue as clearly as possible.

I have a longstanding and worsening AHC problem. Help is requested please from anywhere in the world ….

Despite refurbishments which have included lots of vital new parts, the AHC system on my 2006 LC100 steadfastly refuses to rise to any occasion from “LO” to “N” in anything much less than 38 seconds – after having dropped slowly from “N” to “LO” in 22 seconds.

And yet this vehicle will spring from “N” to “HI” in about 14 seconds on command – and then it is happy to drop back to “N” from “HI” in 8 seconds when required.

The Good Book (FSM) says that upwards movements “LO” to “N” or “N” to “HI” should each take about 15 seconds for a healthy system which has been correctly adjusted and is free of excess weight and other interferences and problems. Downwards movements should take 8 seconds or less.

In addition, the vehicle is erratic and does not settle reliably at the same expected front and rear hub-to-fender heights after an up or down movement or after a road trip.

It does not matter what adjustment I make to the Height Control Sensor adjusters, the vehicle resolutely insists on stopping at “N” from “LO” with Techstream (actually ELMscan327) readings of negative 4 to negative 8 millimetres – nowhere near zero!! It is different and a little better when dropping from “HI” to “N”. It is different again, sometimes with positive readings after returning home from a trip. Then, hub-to-fender distances also become a little higher, often half-inch or a little more, which must mean higher but immeasurable AHC pressures, guessing around 1.1 Mpa additional at the front.

The vehicle does maintain reliable and equal ‘cross level’ hub-to-fender distances within one-eighth of an inch (3 millimetres).

Shortly, my vehicle (see signature line) shortly will leave home on the East Coast of Australia and will be delivered to family members in Perth, Western Australia – about 4,300 kilometres (2,680 miles) away.

Naturally, I do not wish to hand over a ‘lemon’. Many very conservative and pre-emptive refurbishments have been undertaken. Some of these replacements of all new Toyota parts were made pre-emptively for longevity and reliability reasons rather than due to other specific adverse ‘symptoms’ -- in particular because it is easy in Australia to get good help on all Landcruiser matters except the mysteries of AHC/TEMS!! It was time for replacement of ‘globes’ and springs. It also was hoped that most issues also would be resolved by these efforts – but this has not happened. The above behaviour prevails even with some very new parts.

Specific details of the vehicle and suspension status include:
  • Vehicle Age and mileage: built 06/2006, travelled 209,652 kilometres (130,271 miles),
  • Model: HDJ100R-GNAEZQ “Sahara”, with 1HD-FTE turbodiesel, AHC/TEMS, ABS, A-TRAC, VSC, VGRS,
  • Location: Brisbane, Australia,
  • ‘Globes’: replaced 05/2019 (new Toyota parts), still showing today ~14 graduations at AHC Tank between “LO” and “HI”,
  • FR, FL, and Rear Height Control Sensors: all replaced 07/2020 (new Toyota parts),
  • AHC Pump Assembly (pump, motor, pressure and temperature sensors, tank): replaced 10/2020, (new Toyota parts),
  • AHC Height Control Accumulator (long cylinder, includes new solenoid valve): replaced 10/2020 (new Toyota part),
  • Front Suspension: ‘Sweaty’ Front ‘Shock Absorbers’ replaced 09/2016 (new Toyota parts), original Torsion Bars adjusted to correct Front AHC pressures, front wheel bearings replaced and bushes reviewed 05/2020, steering rack reconditioned 09/2019,
  • Rear Suspension: Installed KING KTRS-79 Springs (no spacers) with Firestone airbag assist including Kevlar protectors inside coils 10/2019, also did small Rear Sensor Lift to partially offset low AHC pressures resulting from the higher spring rate of the new springs, also replaced rear LCA’s and rear UCA’s 09/2019,
  • Last AHC Fluid change: 10/2020 (new genuine Toyota AHC Fluid 08886-01805),
  • ARB Deluxe Front Bar with hoops (no winch) per avatar, KAYMAR single wheel carrier (not full bar), Toyota towbar,
  • BFG 275/65R17 KO2 tyres, Load Rating “E”, set at 40 psi for highway cruising,
  • Ride Quality and Comfort: Very Good – as expected, slightly firmer than stock especially when empty, due to choice of tyres and rear springs – but excellent when loaded for touring. Excellent response to COMFORT>>SPORT switch settings.
The first attachment is a Data Sheet which sets out details of tests and measurements carried out on 26th October 2020.

The vehicle sits a little low in these tests – raising the vehicle by pushing all Sensor adjusters up their slides has not improved the situation. Nor have attempts to bring the Sensor read-outs closer to zero where they should be. Instead the vehicle was raised and the negative Sensor readings persisted.

The second attachment shows “stills” from a video I made of the on-screen pressure changes during a “LO” to “N” rise of the vehicle. The videos were made as part of an effort to understand what the Levelling Valves in the Control Valve Assembly were doing and also, if possible, to confirm the operation of the solenoid valve on the Height Control Accumulator. (I am not sure what to make of the trace of the Height Control Accumulator pressure). The video file is too big to attach but the marked-up “stills” give the idea. They show the long response times and slow build-up of pressure. These solenoid valves in the Control Valve Assembly and the Height Control Accumulator have been checked by touch and sound and by the “Active Test” and do seem to be operating. Arthritic fingers have not yet succeeded in removing the electrical connectors and so resistances have not yet been checked per FSM, nor has continuity been checked through to the ECU. The new Height Control Sensors all operate correctly. Hopefully there are no blockages in the tiny filter “socks” inside the new AHC Pump! Underbody condition is excellent with no corrosion and no visible harness damage.

I have wondered whether there is mechanical interference somewhere, such as in the suspension bushings or between the airbags and their covers and the rear springs, when moving between “LO” and “N”. My Independent Mechanic thinks not. It all seems to work very well between “N” and “HI”.

Anyway, this is a long story with a lot of attached detail. All advice, comments, critique, ideas from anyone anywhere about what to do next would be most welcome. May I specifically tag @uHu, @PADDO, @LndXrsr, @Moridinbg, @2001LC, @suprarx7nut, whose insights on such matters always has been helpful.
 

Attachments

  • AHC Test Data Sheet - 26OCT20.pdf
    217.5 KB · Views: 35
  • Pressure sequence HCA and FRONT and REAR 26OCT20.pdf
    469.1 KB · Views: 36

suprarx7nut

The YotaMD Guy
Supporting Vendor
Joined
Sep 28, 2010
Messages
3,750
Location
Colorado
Some comparison from a few others cars is probably needed here. Mine seems slow as well, but it's never been problematic. Your numbers are probably similar to mine.

I was going to suggest the pump is old, but if that's new, I'm not sure what else might be causing that slowness. Kinked line, maybe? Some sort of flow restriction?
 

LndXrsr

AHC Aficionado
SILVER Star
Joined
May 3, 2020
Messages
279
Location
Cincinnati
Indro, you're not the one who's supposed to have problems, you're supposed to be helping fix others' problems! If you're having trouble, this is going to be a difficult challenge for sure.

I'll say, my initial impressions regarding the slowness were: pump, debris in the lines (still possible even after a flush I suppose), and sensors. But you've done all those things and not with junk aftermarket parts.

Second, I don't think your sensor readings are that far off. Within 10mm of zero perhaps isn't "perfect" but it's in the realm of acceptable and 5mm or less is very good. You certainly aren't handing over an AHC lemon to your family with all these new parts and so much care and maintenance put in.

You are on the soft end of the rear pressures and given that more weight is supported by your stout rear springs, that may slow down the N-->L movement, but I would think would help speed up the L-->N process. If you wanted to be super thorough, you could swap stock springs back in and see if things change at all.
 

LndXrsr

AHC Aficionado
SILVER Star
Joined
May 3, 2020
Messages
279
Location
Cincinnati
Some comparison from a few others cars is probably needed here. Mine seems slow as well, but it's never been problematic. Your numbers are probably similar to mine.

I was going to suggest the pump is old, but if that's new, I'm not sure what else might be causing that slowness. Kinked line, maybe? Some sort of flow restriction?

As a comparator, my truck probably is close to the FSM 8 seconds from N-->L. 15-20sec L-->N. So I do think those times are quite long and represent something slightly goofy. At the same time, if it reliably goes into L, N, and H, I'm not sure the time, money, and effort to sort it out beyond what you've already done will net very good returns.
 
Joined
Dec 6, 2016
Messages
249
Location
Brisbane, Australia
Hi All,

Firstly, apologies in advance for this long post. It attempts to describe a current issue as clearly as possible.

I have a longstanding and worsening AHC problem. Help is requested please from anywhere in the world ….

Despite refurbishments which have included lots of vital new parts, the AHC system on my 2006 LC100 steadfastly refuses to rise to any occasion from “LO” to “N” in anything much less than 38 seconds – after having dropped slowly from “N” to “LO” in 22 seconds.

And yet this vehicle will spring from “N” to “HI” in about 14 seconds on command – and then it is happy to drop back to “N” from “HI” in 8 seconds when required.

The Good Book (FSM) says that upwards movements “LO” to “N” or “N” to “HI” should each take about 15 seconds for a healthy system which has been correctly adjusted and is free of excess weight and other interferences and problems. Downwards movements should take 8 seconds or less.

In addition, the vehicle is erratic and does not settle reliably at the same expected front and rear hub-to-fender heights after an up or down movement or after a road trip.

It does not matter what adjustment I make to the Height Control Sensor adjusters, the vehicle resolutely insists on stopping at “N” from “LO” with Techstream (actually ELMscan327) readings of negative 4 to negative 8 millimetres – nowhere near zero!! It is different and a little better when dropping from “HI” to “N”. It is different again, sometimes with positive readings after returning home from a trip. Then, hub-to-fender distances also become a little higher, often half-inch or a little more, which must mean higher but immeasurable AHC pressures, guessing around 1.1 Mpa additional at the front.

The vehicle does maintain reliable and equal ‘cross level’ hub-to-fender distances within one-eighth of an inch (3 millimetres).

Shortly, my vehicle (see signature line) shortly will leave home on the East Coast of Australia and will be delivered to family members in Perth, Western Australia – about 4,300 kilometres (2,680 miles) away.

Naturally, I do not wish to hand over a ‘lemon’. Many very conservative and pre-emptive refurbishments have been undertaken. Some of these replacements of all new Toyota parts were made pre-emptively for longevity and reliability reasons rather than due to other specific adverse ‘symptoms’ -- in particular because it is easy in Australia to get good help on all Landcruiser matters except the mysteries of AHC/TEMS!! It was time for replacement of ‘globes’ and springs. It also was hoped that most issues also would be resolved by these efforts – but this has not happened. The above behaviour prevails even with some very new parts.

Specific details of the vehicle and suspension status include:
  • Vehicle Age and mileage: built 06/2006, travelled 209,652 kilometres (130,271 miles),
  • Model: HDJ100R-GNAEZQ “Sahara”, with 1HD-FTE turbodiesel, AHC/TEMS, ABS, A-TRAC, VSC, VGRS,
  • Location: Brisbane, Australia,
  • ‘Globes’: replaced 05/2019 (new Toyota parts), still showing today ~14 graduations at AHC Tank between “LO” and “HI”,
  • FR, FL, and Rear Height Control Sensors: all replaced 07/2020 (new Toyota parts),
  • AHC Pump Assembly (pump, motor, pressure and temperature sensors, tank): replaced 10/2020, (new Toyota parts),
  • AHC Height Control Accumulator (long cylinder, includes new solenoid valve): replaced 10/2020 (new Toyota part),
  • Front Suspension: ‘Sweaty’ Front ‘Shock Absorbers’ replaced 09/2016 (new Toyota parts), original Torsion Bars adjusted to correct Front AHC pressures, front wheel bearings replaced and bushes reviewed 05/2020, steering rack reconditioned 09/2019,
  • Rear Suspension: Installed KING KTRS-79 Springs (no spacers) with Firestone airbag assist including Kevlar protectors inside coils 10/2019, also did small Rear Sensor Lift to partially offset low AHC pressures resulting from the higher spring rate of the new springs, also replaced rear LCA’s and rear UCA’s 09/2019,
  • Last AHC Fluid change: 10/2020 (new genuine Toyota AHC Fluid 08886-01805),
  • ARB Deluxe Front Bar with hoops (no winch) per avatar, KAYMAR single wheel carrier (not full bar), Toyota towbar,
  • BFG 275/65R17 KO2 tyres, Load Rating “E”, set at 40 psi for highway cruising,
  • Ride Quality and Comfort: Very Good – as expected, slightly firmer than stock especially when empty, due to choice of tyres and rear springs – but excellent when loaded for touring. Excellent response to COMFORT>>SPORT switch settings.
The first attachment is a Data Sheet which sets out details of tests and measurements carried out on 26th October 2020.

The vehicle sits a little low in these tests – raising the vehicle by pushing all Sensor adjusters up their slides has not improved the situation. Nor have attempts to bring the Sensor read-outs closer to zero where they should be. Instead the vehicle was raised and the negative Sensor readings persisted.

The second attachment shows “stills” from a video I made of the on-screen pressure changes during a “LO” to “N” rise of the vehicle. The videos were made as part of an effort to understand what the Levelling Valves in the Control Valve Assembly were doing and also, if possible, to confirm the operation of the solenoid valve on the Height Control Accumulator. (I am not sure what to make of the trace of the Height Control Accumulator pressure). The video file is too big to attach but the marked-up “stills” give the idea. They show the long response times and slow build-up of pressure. These solenoid valves in the Control Valve Assembly and the Height Control Accumulator have been checked by touch and sound and by the “Active Test” and do seem to be operating. Arthritic fingers have not yet succeeded in removing the electrical connectors and so resistances have not yet been checked per FSM, nor has continuity been checked through to the ECU. The new Height Control Sensors all operate correctly. Hopefully there are no blockages in the tiny filter “socks” inside the new AHC Pump! Underbody condition is excellent with no corrosion and no visible harness damage.

I have wondered whether there is mechanical interference somewhere, such as in the suspension bushings or between the airbags and their covers and the rear springs, when moving between “LO” and “N”. My Independent Mechanic thinks not. It all seems to work very well between “N” and “HI”.

Anyway, this is a long story with a lot of attached detail. All advice, comments, critique, ideas from anyone anywhere about what to do next would be most welcome. May I specifically tag @uHu, @PADDO, @LndXrsr, @Moridinbg, @2001LC, @suprarx7nut, whose insights on such matters always has been helpful.

Thank you all for comments so far. Probably @ramangain is right! However, my well-cultivated obsessive-compulsive inner self was not quite ready to let me to concede, so I kept looking for the ‘cause’ of the current ‘effects’ ….

No physical adjustments have been made since the previous tests and measurements which were done on 26th October 2020, as set out on the Data Sheet attached to Post #1 in this thread.

On return from a short trip, I noticed that the car was sitting a little higher.

Started engine again, drove out of the garage, then back in, just to be sure that the AHC system and pump had finished doing their thing and that the suspension had settled. While the engine was still running with AHC “ON”, measured all hub-to-fender distances (to the nearest one-eighth inch):

FR hub-to-fender: 19.875 inches (previously, after LO>> N: 19.250 inches)
FL hub-to-fender: 20.000 inches (previously, after LO>> N: 19.250 inches)
RR hub-to-fender: 20.875 inches (previously, after LO>> N: 20.500 inches)
RL hub-to-fender: 20.750 inches (previously, after LO>> N: 20.500 inches)

FR Height Control Sensor: +11.4 millimetres (previously, after LO>> N): – 5.0 millimetres
FL Height Control Sensor: +12.4 millimetres (previously, after LO>> N): – 4.2 millimetres
Rear Height Control Sensor: – 2.8 millimetres (previously, after LO>> N): – 8.0 millimetres

Mmmmm – confusion! This is a long, long way different to my previous measurements N >> LO >> N following the FSM procedure. What should be made of the above height differences and sensor differences? Why does this happen? Does it simply mean that this is where the suspension landed at the time the vehicle has stopped at engine OFF but that suspension has not yet ‘self-levelled’?

However, this situation happens repeatedly.

The ‘control loop’ should result in the ECU causing the suspension to stop at or close to zero height sensor readings (possibly with minor adjustable differences between sensors to allow for manufacturing differences, wear and tear differences, etc). This is the design. It should happen regardless of the actual hub-to-fender operational height setting chosen by the Owner, provided that system faults or Owner errors have not caused the ECU to override with ‘fail-safe’ settings as defined in the FSM. Note: The Height Control Sensors are new.

No Diagnostic Trouble Codes (DTC’s) are present. On the road, the system feels normal and behaves normally. Physical responses to the four-position COMFORT >> SPORT console switch are good, the Front and Rear Wheel Step positions are visible on the read-out, also the variations with each console switch positions on the read-out can be seen while moving. The different combinations of the Damper Force Switches also can be seen on the read-out screen. (For these purposes, I attach the screen to the windscreen for observation purposes while the vehicle is moving).

No physical AHC/TEMS ‘fail safe’ symptoms are present.

Drove out of the garage, around the local streets and back into the garage. With engine and AHC still “ON”, got out of the vehicle and re-measured. The high operating hub-to-fender measurements and the high sensor readings were much the same as recorded above.

What does it mean for front and rear AHC pressures at these increased heights? How can these be measured in real time?

What the hell, I thought, let’s do another N >> LO >> N height movement per FSM and measure everything yet again! This resulted in the following: (tape measurements to nearest one-eighth inch)

Times: N >> LO: 21 seconds and LO >> N: 38 seconds (both similar to the very long times in previous measurements on 26th October 2020)

This time, with my head poised over the AHC Pump, I noticed that the pump started immediately that the LO >> N raise began (when I closed the vehicle door).

I could not tell whether pump operation was as well as, or instead of, the Height Control Accumulator releasing its pressure to initiate the raise, as it should do when fully charged and raising from LO to N. The Height Control Accumulator and its attached Solenoid Valve are new. The AHC Pump continued throughout this long duration raise until the dashboard light stopped blinking and remained steady at N and then continued for another 15 seconds (timed).

I waited another 60 seconds with engine running, then measured ….

FR hub-to-fender: 19.125 inches (previously, after LO>> N): 19.250 inches
FL hub-to-fender: 19.250 inches (previously, after LO>> N): 19.250 inches
RR hub-to-fender: 20.500 inches (previously, after LO>> N): 20.500 inches
RL hub-to-fender: 20.625 inches (previously, after LO>> N): 20.500 inches

…. and Techstream (ELMscan327) readings:

FR Height Control Sensor: – 4.6 millimetres (previously, after LO>> N: – 5.0 millimetres)
FL Height Control Sensor: – 5.0 millimetres (previously, after LO>> N: – 4.2 millimetres)
Rear Height Control Sensor: –7.6 millimetres (previously, after LO>> N: – 8.0 millimetres)

Front Pressure: 6.9MPa; Rear Pressure: 5.8 MPa (previously, after LO>> N: Front: 6.9 MPa; Rear: 5.7 MPa)

Mmmm – back to where we were. These new, timed, tape-measured and re-tested N >> LO >> N results are all reasonably consistent with the earlier N >> LO >> N results on 26th October 2020 as shown on the Data Sheet attached to Post #1 in this thread.

Then I thought, for the last experiment of the weekend, let’s see what happens when the pressures and heights build while on the move, instead of the static situation in the garage in the conditions prescribed by FSM. This meant that, different to all previous tests, I would be in the vehicle.

With vehicle stopped on a level road, dropped height to LO. Started Techstream (ELMscan327) and drove at 10 kilometres per hour (6 miles per hour), until vehicle raised to N and dashboard light stopped blinking. (FSM states that “When the vehicle height is at LO, vehicle is automatically raised to N when the vehicle speed becomes higher than 5 kilometres per hour (3 miles per hour). At this time, the fluid stored in the Height Control Accumulator also is used”. I could hear the AHC Pump running, maybe recharging the accumulator). Note: The AHC Pump Assembly and the Height Control Accumulator are new.

Return to garage, engine still ON, got out of the vehicle to re-measure hub-to-fender distances:

Tape measurements (to nearest one-eighth inch):

FR hub-to-fender: 19.750 inches
FL hub-to-fender: 19.750 inches
RR hub-to-fender: 20.875 inches
RL hub-to-fender: 20.875 inches

Techstream (ELMscan327) readout (engine still ON, driver now out of vehicle):

Readings at approx 10kph with driver on board - 02NOV20.jpg


Again, all very different to the N >> LO >> N static tests as prescribed by FSM and as repeated several times and recorded above. This time the Front Sensor readings are positive and the Rear Sensor reading is slightly negative. Uncertain whether the higher Front and Rear AHC pressures in this read-out are due to the greater heights, or my presence in the vehicle, or both.

Investigations continue.

As previously, all comments and advice are welcome.
 
Joined
Mar 25, 2019
Messages
845
Location
NWFL
For a comparison my 1999 LX with 186k miles takes about 5 seconds from N to L, then another 5 to 6 from L to N. It took about 8 seconds to go from N to H.

I have a front bumper only
 

uHu

Bridgeburner
Joined
Nov 27, 2005
Messages
2,062
Location
Oslo, Norway
Two causes for slow N-L-N that I have observed:
One - is if a sensor (or more) is bad, giving a varying signal, the system can take a long time finding out "where it is". This seems unlikely in your case.
The second - is if the height is adjusted too low, or if the car is parked so that the rear right wheel is higher than the left (sensor is towards left side), it will have problems reaching normal Lo height. It will lower the pressure a bit extra, as much as possible, and at the end give up and say "OK, this is Lo", even if it isn't as low as Lo normally is. In those cases I see that it also takes a long time before it starts moving up again, towards N. It might have to do with a lower pressure than standard at position Lo, and therefore more fluid to pump. Having King Springs could do a bit of the same, making it more difficult to reach Lo. You could test the theory by setting the rear height higher by an inch or more, so that it will easier reach the sensor's Lo position.
 

LndXrsr

AHC Aficionado
SILVER Star
Joined
May 3, 2020
Messages
279
Location
Cincinnati
I'll agree with uHu that you have bad sensor symptoms (widely varying sensor height readings on Tachstream), but with new OEM sensors. I'd double check the plugs and wiring to the sensors seems solid. Any intermittent shorts might result in findings similar a bad sensor, even though the sensor itself is okay.
 
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