AHC tech scan, what does the data mean?

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2001LC

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I can use some help here guys? In reading the tea leaves... Of IG & +B Power source voltage. Can anyone tell me, what Voltage is tell indicating and where reading comes from?

So I've never really looked a voltage before. Typically I've just been concerned with FR, FL & RR height control sensor inch, Front, Rear & Accumulator pressure sensor Mpa and temperature (F).

I'm now looking at IG & +B Power source voltage. Can anyone tell me, what Voltage is tell indicating and where reading comes from?

Here a typicality tech stream scan. Where I've raise to high and low a few times, than L to N and took reads. While Temperature sensor unplugged, reads -22f. Heights at 0.00 to -0.1,. Mpa frt 6.9, Rear 6.3 & acc 10.4 Mpa. IG voltage 13.7 and +B at 14.1 volts.

AHC 2020-10-10.JPEG


Here same 00LX about a years later. Height -0.1 to -0.0. Frt 6.8, Rear 6.4Mpa & Acc 10.4Mpa. Temp 100F (Temp sensor happen to be plugged in), all others not to much difference form those earlier reading.
But notice voltages.
IG 13.7V and now +B voltage at 12.9V is lower the IG voltage?

AHC 21-3-3.JPEG


Here is an 01LX,with some yet undermined AHC failure (In fail safe, OFF light flashing) issues.
In this while work temperature would raise fast and get high. I've seen 131F.
Note the Voltage now. Interestingly the IG voltage is always ~ 1 volt lower than the battery (checked battery with meter). The +B voltage always very low. I can not use active test. It shuts system down instantly putting into fail safe. I may see as it does try to run say Accumulator +B gets up to around ~7V, but drops back down fast.
IMG_6538.JPEG
 
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Anyone have a handle on the IG Voltage & +B voltage reads, and what they are tell us?
 
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Negative. @IndroCruise is probably the guy to tag here.
 
I can use some help here guys? In reading the tea leaves... Of IG & +B Power source voltage. Can anyone tell me, what Voltage is tell indicating and where reading comes from?

So I've never really looked a voltage before. Typically I've just been concerned with FR, FL & RR height control sensor inch, Front, Rear & Accumulator pressure sensor Mpa and temperature (F).

I'm now looking at IG & +B Power source voltage. Can anyone tell me, what Voltage is tell indicating and where reading comes from?

Here a typicality tech stream scan. Where I've raise to high and low a few times, than L to N and took reads. While Temperature sensor unplugged, reads -22f. Heights at 0.00 to -0.1,. Mpa frt 6.9, Rear 6.3 & acc 10.4 Mpa. IG voltage 13.7 and +B at 14.1 volts.

View attachment 2985387

Here same 00LX about a years later. Height -0.1 to -0.0. Frt 6.8, Rear 6.4Mpa & Acc 10.4Mpa. Temp 100F (Temp sensor happen to be plugged in), all others not to much difference form those earlier reading.
But notice voltages.
IG 13.7V and now +B voltage at 12.9V is lower the IG voltage?

View attachment 2985396

Here is an 01LX,with some yet undermined AHC failure (In fail safe, OFF light flashing) issues.
In this while work temperature would raise fast and get high. I've seen 131F.
Note the Voltage now. Interestingly the IG voltage is always ~ 1 volt lower than the battery (checked battery with meter). The +B voltage always very low. I can not use active test. It shuts system down instantly putting into fail safe. I may see as it does try to run say Accumulator +B gets up to around ~7V, but drops back down fast.
View attachment 2985409

Probably you have already done this, but for completeness suggest check and test battery and charging system – the method probably is well-known to you but also see description at

LC100 Workshop Manual - https://lc100e.github.io/

then the following further tabs:

Engine Repair Manual [2UZ-FE] > CHARGING > CHARGING SYSTEM (Page CH1 or Page CH2 depending on Model Year)

Anyway, assuming that the charging system is in good order and returning to your screenshots ….

I don’t understand what causes the Techstream message “Lost Communication with the vehicle” but maybe that is not particularly relevant.

The first screenshot -- shows one unidentified DTC – temperature is -22degF, so this DTC would be due to temperature sensor being disconnected, otherwise all values look normal in all respects, including IG 13. 7 volts and +B 14.1 volts. Interesting -- don’t recall seeing +B greater than IG on other AHC screenshots on IH8MUD – but maybe I have not been observant enough and/or maybe that just represents a fully charged battery in good condition? Or does it suggest a alternator/regulator on the way out?

The second screenshot – shows no DTC’s, temperature 100degF seems reasonable, all other values look reasonable in all respects, including IG 13. 7 volts and +B 12.9 volts – with +B is 0.8 volts lower than IG and also +B is 1.2 volts less than +B in the first screenshot.

These IG and +B voltages on the second screenshot do not seem unusual to me and are consistent with most other screenshots I have seen on IH8MUD over recent years. My own most recent results (DEC ’21) with vehicle operating normally with new batteries (two in parallel in 1HD-FTE) and new OEM replacement Toyota/Denso 27060-17230 alternator (long story!) were:

IG 14.0 volts and +B 13.2 volts
IG 13.8 volts and +B 12.9 volts

The third screenshot is a puzzle. It shows one unidentified DTC, not temperature sensor this time, temperature is high at 129degF suggesting pump has been working hard (?), height sensors are all high but closely grouped within 0.3 inches of each other, Front and Rear AHC pressures are somewhat high – maybe corresponding to height of vehicle (?), Main Relay Expectation is “OFF” (?) but “ON” on previous screenshots, IG 12.1 volts (low), +B 1.7 volts (extremely low).

Ordinarily, this would raise suspicions about an under-charged battery as would expect to see around 13 volts on the distribution system from the battery. Assuming the charging system is healthy, that would suggest checking the 15Amp AHC-B fuse and the 20Amp AHC-IG fuse (both in the junction box behind the kickboard on the LHS of the LHD driver’s footwell) and also checking the operation of the AHC Main Relay (which is mounted on the AHC ECU under the dashboard.

In theory
, nothing is going to happen, including “Active Test”, in the AHC/TEMS systems if these items are preventing delivery of electrical power.

However, in practice the third screenshot also shows that the vehicle has been raised with reasonable although somewhat high Front and Rear AHC pressures and normal Height Control Accumulator pressure. This did not happen without the operation of the AHC system – or are these readings old readings which have not been cleared from the ECU??

The third screenshot shows a DTC – has it been possible to identify this DTC?

The ECU response to disable AHC (and initiate protective ‘fail-safe functions) could happen in 0.5 seconds or 2 seconds (if C1743 depending on circumstances), or in 0.6 seconds (if C1762).

So apologies @2001LC – I don’t get what has happened in the circumstances depicted in the the third screenshot. As a Iate edit I have wondered if the vehicle is still capable of being raised by the AHC system-- perhaps slowly compared to expectation -- then a possibility might be a partially blocked AHC Pump -- but that does not fit with the voltage readings which suggest that neither the AHC circuit nor the AHC Pump is receiving electrical power. There must be a better answer -- I think I am missing something.

Hopefully other IH8MUD Members can be more helpful! Maybe @Rebus Knebus or @YvesNL given some of their previous posts on similar topics??

As well as the charging reference given far above, I have had a look at the following references:

LC100 Workshop Manual - https://lc100e.github.io/ (This is an LC100 FSM but should be good enough for LX470 purposes).

then follow these tabs in the menu on LHS of opening page:

Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS

then the following further tabs:

Power Source Circuit (Page DI-294) – with engine running, need battery voltage (+B) of 10 volts to 16 volts, and, ECU terminal voltage (IG) of 9 volts to 14 volts – to enable operation of AHC Pump & Motor and Damping Force Control Actuators (TEMS). If not, check/test the circuit as described, including AHC-IG fuse (behind LHS cover in LHS footwell) and continuity of harness and connectors back to ECU. [Note: These voltages only define what the AHC ECU would accept -- see the first reference far above for the necessary voltage specifications for a healthy Charging System].

also

Tc Terminal Circuit (Page DI-306) – check/test correct voltage is present at terminals DLC3 socket under dash used for Techstream (otherwise Techstream will not operate correctly).

also

Ts Terminal Circuit (Page DI-308) – further check/test correct voltage is present terminals at DLC3 socket under dash used for Techstream (otherwise Techstream will not operate correctly).

then

C1741 – AHC Motor Relay Circuit (Page DI-243) -- check/test whether the relay is working – if not, no power to AHC Pump, ‘fail-safe function’ occurs as described, and there is no AHC/TEMS operation.

and especially

C1743 – AHC Main Relay Circuit (Page DI-248) -- check/test whether the relay (mounted on ECU) is working – if not, no power is supplied to the ECU or any part of the AHC system, ‘fail-safe function’ occurs as described (note the three different conditions, 1 or 2 or 3 which are difficult to understand!) -- response times are 0.5 seconds or 2 seconds (depending on circumstances), then there is no AHC/TEMS operation including “Active Test”.

C1762 – Fluid Pressure Abnormality -- Pump & Motor Does Not Supply Fluid (Page 256) – check/test circuit, note that the response time is very quick ~0.6 seconds to protect pump -- and then there is no AHC/TEMS operation including “Active Test”.
 
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Probably you have already done this, but for completeness suggest check and test battery and charging system – the method probably is well-known to you but also see description at

LC100 Workshop Manual - https://lc100e.github.io/

then the following further tabs:

Engine Repair Manual [2UZ-FE] > CHARGING > CHARGING SYSTEM (Page CH1 or Page CH2 depending on Model Year)

Anyway, assuming that the charging system is in good order and returning to your screenshots ….

I don’t understand what causes the Techstream message “Lost Communication with the vehicle” but maybe that is not particularly relevant.

The first screenshot -- shows one unidentified DTC – temperature is -22degF, so this DTC would be due to temperature sensor being disconnected, otherwise all values look normal in all respects, including IG 13. 7 volts and +B 14.1 volts. Interesting -- don’t recall seeing +B greater than IG on other AHC screenshots on IH8MUD – but maybe I have not been observant enough and/or maybe that just represents a fully charged battery in good condition? Or does it suggest a alternator/regulator on the way out?

The second screenshot – shows no DTC’s, temperature 100degF seems reasonable, all other values look reasonable in all respects, including IG 13. 7 volts and +B 12.9 volts – with +B is 0.8 volts lower than IG and also +B is 1.2 volts less than +B in the first screenshot.

These IG and +B voltages on the second screenshot do not seem unusual to me and are consistent with most other screenshots I have seen on IH8MUD over recent years. My own most recent results (DEC ’21) with vehicle operating normally with new batteries (two in parallel in 1HD-FTE) and new OEM replacement Toyota/Denso 27060-17230 alternator (long story!) were:

IG 14.0 volts and +B 13.2 volts
IG 13.8 volts and +B 12.9 volts

The third screenshot is a puzzle. It shows one unidentified DTC, not temperature sensor this time, temperature is high at 129degF suggesting pump has been working hard (?), height sensors are all high but closely grouped within 0.3 inches of each other, Front and Rear AHC pressures are somewhat high – maybe corresponding to height of vehicle (?), Main Relay Expectation is “OFF” (?) but “ON” on previous screenshots, IG 12.1 volts (low), +B 1.7 volts (extremely low).

Ordinarily, this would raise suspicions about an under-charged battery as would expect to see around 13 volts on the distribution system from the battery. Assuming the charging system is healthy, that would suggest checking the 15Amp AHC-B fuse and the 20Amp AHC-IG fuse (both in the junction box behind the kickboard on the LHS of the LHD driver’s footwell) and also checking the operation of the AHC Main Relay (which is mounted on the AHC ECU under the dashboard.

In theory
, nothing is going to happen, including “Active Test”, in the AHC/TEMS systems if these items are preventing delivery of electrical power.

However, in practice the third screenshot also shows that the vehicle has been raised with reasonable although somewhat high Front and Rear AHC pressures and normal Height Control Accumulator pressure. This did not happen without the operation of the AHC system – or are these readings old readings which have not been cleared from the ECU??

The third screenshot shows a DTC – has it been possible to identify this DTC?

The ECU response to disable AHC (and initiate protective ‘fail-safe functions) could happen in 0.5 seconds or 2 seconds (if C1743 depending on circumstances), or in 0.6 seconds (if C1762).

So apologies @2001LC – I don’t get what has happened in the circumstances depicted in the the third screenshot. As a Iate edit I have wondered if the vehicle is still capable of being raised by the AHC system-- perhaps slowly compared to expectation -- then a possibility might be a partially blocked AHC Pump -- but that does not fit with the voltage readings which suggest that neither the AHC circuit nor the AHC Pump is receiving electrical power. There must be a better answer -- I think I am missing something.

Hopefully other IH8MUD Members can be more helpful!

As well as the charging reference given far above, I have had a look at the following references:

LC100 Workshop Manual - https://lc100e.github.io/ (This is an LC100 FSM but should be good enough for LX470 purposes).

then follow these tabs in the menu on LHS of opening page:

Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS

then the following further tabs:

Power Source Circuit (Page DI-294) – with engine running, need battery voltage (+B) of 10 volts to 16 volts, and, ECU terminal voltage (IG) of 9 volts to 14 volts – to enable operation of AHC Pump & Motor and Damping Force Control Actuators (TEMS). If not, check/test the circuit as described, including AHC-IG fuse (behind LHS cover in LHS footwell) and continuity of harness and connectors back to ECU. [Note: These voltages only define what the AHC ECU would accept -- see the first reference far above for the necessary voltage specifications for a healthy Charging System].

also

Tc Terminal Circuit (Page DI-306) – check/test correct voltage is present at terminals DLC3 socket under dash used for Techstream (otherwise Techstream will not operate correctly).

also

Ts Terminal Circuit (Page DI-308) – further check/test correct voltage is present terminals at DLC3 socket under dash used for Techstream (otherwise Techstream will not operate correctly).

then

C1741 – AHC Motor Relay Circuit (Page DI-243) -- check/test whether the relay is working – if not, no power to AHC Pump, ‘fail-safe function’ occurs as described, and there is no AHC/TEMS operation.

and especially

C1743 – AHC Main Relay Circuit (Page DI-248) -- check/test whether the relay (mounted on ECU) is working – if not, no power is supplied to the ECU or any part of the AHC system, ‘fail-safe function’ occurs as described (note the three different conditions, 1 or 2 or 3 which are difficult to understand!) -- response times are 0.5 seconds or 2 seconds (depending on circumstances), then there is no AHC/TEMS operation including “Active Test”.

C1762 – Fluid Pressure Abnormality -- Pump & Motor Does Not Supply Fluid (Page 256) – check/test circuit, note that the response time is very quick ~0.6 seconds to protect pump -- and then there is no AHC/TEMS operation including “Active Test”.
Thanks for dropping in, and taking the time here. You are such a comprehensive and talented writer with a good grasp on AHC. I was hoping you would help out here, THANK YOU!. I've read the link you once gave me, "new model outline, AHC". Very good info, I'd never read/seen before. Thank you!

I also hope others like @PADDO @suprarx7nut @uHu just to mention a few, stop by. As I'm seeing some tough cases, and I can use help on them.

The first two pictures in OP of tech stream, are old file pic's. One's form my 00LX470 w/670,000K (~360K miles), which I've a thread in mud on. It's AHC, works okay. One could say very good, considering age and miles. Those where just old pictures I had on hand, that I posted here for comparison. I never really looked at voltage before now. I found the +B voltage being higher than IG curious also. Perhaps it has to do with temperature senors being unplugged as does the -22F temperature.

The: "Lost Communication with the vehicle” seen in first two tech stream screen shots. Is just because I lose connection with tech stream, when I turn Key ( IG SW) to OFF to to off engine.

Thank you the very thoughtful and well written diagnostic tree. I've done many, but not all. I'm going back through all next few days.

Battery & charging system, seems to be working well. Battery holds about 12.5 to 12.7 on its'a own. I get 13 to 14 engine running. Battery was sulfate last December, but my charger corrected. Although I do have some concern with electric system (not charging system at this point), as some history of electrical gremlins with LH DS mirror and steering column motor. Seem 2 different Dealership years apart. Replaced a CPU (IIRC, I'll double check on what was R&R later) for DS mirror. It keeps failing, as does steering tilt.

I do have a C1736, C1736 DTC currently. The C1736 came up after unplugging all 3 wire housing blocks at pump (Motor power, also pressure and temp sensors)

I'll come back to current issue in next post. But first some history on this 2001 LX470:
__________________________________________________________________________
Sorry this is going to be long:

I'm first going to give history of this 2001, which is 3rd picture with the very low +B voltage. I'll use a subsequent post to talk about current issue with it.

The third picture is of a 2001LX w/145K miles. I'll give a little history on: NOTE: THIS IS FIRST AHC ISSUE IN 2021. It has now come back with AHC issue I'll come back subsequently with current 2022 ISSUES. But first some history on 2021

It's a clean, rust free 100 series on it's 3 rd owner. No know accidents or signs of. First owner keep in a Garage IIRC in Vail CO, best we can tell. Indications, were it sat extended periods not driven, with first owner.

2nd owner brought to me, to repair of LH mirror and steering wheel tilt not functioning. I found both motors and SW's worked. Once I jump steering tilt motor with 12Volt by use of telescoping wire harness, it began reluctantly working. Was able to get mirror working through tech stream. The more I used them both, the more reliable they functioned. I chocked it up to lack of use. 100 series like all system used frequently. Most notably component we see issues with when not, is the CDL. Anyway I recommend, baseline including flush and adjust of AHC. But never I did any of that, and found it was never done by second owner.

3rd owner.
He brought to me when AHC failed, after buying and driving for sometime:

AHC OFF flashing, ride bounce, both front and rear high (rear was extra high).
It was taken to a Toyota Dealership before bring to me, without results. Only a statement "CUST MAX 1 hr diagnostic time","not enough time to diagnos". He was charged 1hr.

I found (Dec 2021):
AHC flashing OFF on dash lights.
* Sensor arms frozen. (Note "A" bottom of page)
Ride height high and bouncy.
DTC: C1736 Accumulator Solenoid Circuit.
DTC: C1762 Abnormal Oil Pressure for pump.
Going through diagnostic tree in FSM. In tech steam, activating relays & solenoids, I'd get: "ECU cannot perform the request Active test"


IMG_4579.JPEG
I did NOT do one test, in tree. In which we 're directed to test pressure sensor. But moved on to looking at ECU, as it seem I could not get any response from it. But I could hear sound from it or it's relay on the side of it. Which FSM direct us to listen for sound as IIRC.

It was my first time trying to take out a AHC ECU. I saw this was going to be very tough & time consuming to get in and out. I considered calling one supper nice mud guy @RicardoJM, who's in my neighborhood. He let me pull AHC stuff off his LX, which he convert to non AHC years ago. I was thinking, I'd pull his computer and plug it into this rig as a test.

But first knowing Andy (@suprarx7nut) had pulled one (AHC ECU). I called Andy. He said: he followed same tree. Although it direct us to test ECU, it was not the issue (or was not on one he worked). He found a dead wire under rear 1/4 near rear bumper on LH side. Nice work Andy... Kudos!

So I started looking around under rear 1/4 LH, Rear sensor back to rear LH corner of bump. Found the wire block housing and unplugged it, then plugged back in. I did get some results.

IMG_6527.JPEG


IMG_6528.JPEG


IMG_6529.JPEG

I went on to find the rear sensor damaged, not just frozen adjuster arm. First I unplug & re-plugged in, and system worked but height wrong. I disconnect arm and set height sensor by hand. I was able to get to height to change. Eventually I remove straighten bracket of sensor and cleaned it. AHC system than worked. But failed again after a few drives. So I installed a replacement rear sensor. System now work heights near normal.

Adjusted sensors & T-bars, after replacing front senor arms and rear season w/arm. To get heights and pressure near factory as I could. With a few drives around the block (1 miles with bumps and turns) between T-bar adjustments. I turned LH t-bar 6CW and RH 3CW Mpa now
Ending readings: Frt 19 1/4" RH & LH, rear 20 3/8". Frt 6.9, Rear 6.5, Accu 10.6 Mpa w/ 10 graduations.

AHC system now working as it should. Comfort to Sport had good response. Damping in turns very nice raised and lowed within spec times. Braking damping good. Nice ride. All in all, very nice.

But failed again on a longer drive. One in which I actively raised and lowered many times. Then while braking, AHC failed, light flashing OFF.

I drove until I could pull over (about 15 minutes). Turned key off and on again starting engine. AHC began work normally. My though was excessive and rapidly raising and lowering, heated fluid. Either heat trip or lower pressure further dropped by heat, caused this failure. I tried a few more time to get to fail, by raising and lower often at every stop. It did fail. Let it cool and began working again.

My though was pressure had gone to high, after driving and settling in. Which resulted in over working the system heating fluid. I see pressures a little change often, especial with old globes after settling in. So I hook-up tech stream and sure enough pressure are up. I don't recall to what, but cranked on T-bars CW, dropping pressure again. Dove for a week actively use L-N-H and confront to sport. No issues handled and rode very nice.

Owner pick up and report drive home through the mountains was outstanding.

3 months later it failed again. :frown:

* Notes: I'd not mentioned sensor arm frozen earlier. I had found all 3 sensor's arms frozen, in first look-over. This has become very common to see these ball of adjuster arm frozen in socket. So much so, I've started a new PM: lubing the AHC adjuster arms. I do this with moly grease and a needle attachment on end of grease gun. I inject grease under (from inner side), not through the boot. The hopes is extending life of these arms. But eventually IMHO,all will need replacing.

Front sensor arm frozen and bent
IMG_4583.JPEG
 
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Like your note on lubing the adjuster arms. I may look into doing that.

The problem obviously sounds electrical, as you allude to, and your interest in the +B voltage makes sense from that standpoint. something seems to be telling the AHC ECU there isn’t enough voltage to run things properly. Indro’s post suggests you need to be at 10-16V.

To clarify, you have checked the relays Indro mentioned above?

If so, this seems like an ECU (which you’ve said you ruled out) or a random wire near the ECU or pump that is frayed, intermittently shorting, etc. and resulting in the low +B voltage reading at the ECU (I assume this is where the voltage is read). This car’s history of electrical hemline is not encouraging. It may take a very careful combing of the wires to ensure things are all intact.
 
Like your note on lubing the adjuster arms. I may look into doing that.

The problem obviously sounds electrical, as you allude to, and your interest in the +B voltage makes sense from that standpoint. something seems to be telling the AHC ECU there isn’t enough voltage to run things properly. Indro’s post suggests you need to be at 10-16V.

To clarify, you have checked the relays Indro mentioned above?

If so, this seems like an ECU (which you’ve said you ruled out) or a random wire near the ECU or pump that is frayed, intermittently shorting, etc. and resulting in the low +B voltage reading at the ECU (I assume this is where the voltage is read). This car’s history of electrical hemline is not encouraging. It may take a very careful combing of the wires to ensure things are all intact.
I want to be clear. All the above in post #6. Is basically before current failure. Post #6 is from back in Dec 21-Jan 22. The testing, parts installed & adjusting were all at that time. Just the 3rd picture in OP, of AHC date is current. Clue: each picture has a date/time in lower RH corner.

The charging systems seems to be working fine. Although, other than checking voltage at battery, no other test were performed. I noted the voltage, IG 13.1 voltage being 1 volt lower than battery. Battery was 14.1 volts, idling on start up. It's not had any cranking of starting issues. But I will add this. After it left me in Jan 2022 working perfectly. It reportedly worked perfectly, until after and aftermarket radio and AMP installed. I had to prob, on when failing began. Which I found after AMP/radio installed. Knowing history and see the IG 1 volt lower than battery voltage idling and +B voltage very low. Lead me to question what these reading are pointing us to. But this may just be a side effect of system in failsafe, IDK. It is why I start thread, in part.

I was given some conflicting info as to mileage between Jan (out) to Mar 2002 (back IN, mileage). In that I was told, it had only been driven only 300 or 400 miles. Odometer has ~2,500 more miles. T\Also the new radio AMP, is very powerful. So much so, volume turned up more than ~20% is speak blowing. I did disconnect AMP at battery. But Radio/Camera LED remains on (Powered). No change in AHC, while in failsafe.

I've done only minimal testing this time in (Current failure). This weekend I'm going back to square one testing. h
_________________________________________________

Now I'll talk a little more about this failure, what I've done and noted. As it came back to me in march 2022. Which I've hand very little time to devote to it, due to other commits.

I was told failure was intermittent. That after parked awhile, system would come back on and seems to work fine when it did. That on the drive back to me from Vail. Which is ~100 miles through the mountains on I-70 East. AHC reportedly, failed about 40 minutes into the drive, working fine until that point. My first through was fluid getting hot.

It was dropped off, parked in my Driveway AHC flashing OFF (front higher than rear). I let it sit overnight before checking AHC, by starting engine the next day. I though it would have cooled and been working by then. It was not working (AHC OFF flashing).
NOTES: My driveway has about an 8% uphill grade, street to shop door. Unrelated to AHC, side note: E-brake handle pulling up, much higher than Jan 2022.

I wanted to start visual inspection, back at the wire harness RH rear 1/4, by unplugging and plugging back in. As this was the place I first got a response from AHC, back in Dec 21. But found the vehicle way to dirty with road sands/crud, to get under and see anything. So moved into street (near level ground leaning low on RH) and parked, so I could power washed. After about hour of power washing the undercarriage, with very cold (winter) water, with special attention to all areas with AHC component. After which, AHC began working again? Great, now I could check to see if pressure went up again, like it did after Dec 21 first test drives (after sensor work & adjust).

Pulled into shop forward, AHC failed again (Flashing OFF)
Pulled rear 1/4 wire block, plugged back in. AHC working again. Hum!
AHC off again. Unplugged, plugged back in. AHC not working. Darn!

Decided to back out of shop and back in. So I could work more easily, at rear 1/4 LH wire harness. AHC was now working again. So I was able to read data through tech stream.

Pressure where out of spec again?
Finding front in a ranging of 8.2 to 8.6 Mpa, as I cycled UP & DN a few times. Rear was 6.2 to 6.5 Mpa. Fluid temp came up fast to 131F (not shown in screen shot below), as I cycled. DTC C1736 (Accumulator Solenoid circuit). These pressure increase, I found interesting. Seemingly pointing to globe(s) failure, front(S) perhaps.
FSM: DTC C1736 Possibles: Open or short circuit in accumulator solenoid circuit: 1) Accumulator solenoid 2) Accumulator solenoid circuit

IMG_6523.JPEG



I adjust T-bars 2CW (clock wise) yet again, taking pressure off AHC, loading onto T-bars.

Starting with only 2CW LH & RH on T-bat. Pressure drop more than expected. Now at frt 6.5, rear 6.5, accumulator 10.4 Mpa.
Front pressure drop ~2Mpa, on only 2CW T-bar RH & LH?
IMG_6535.JPEG


Here's a shot of temp at 131F. I just happen to have on hand. It show main relay OFF I don't recall why.

IMG_6539.JPEG



Any next day AHC working. I decided to take a long test drive, of at least 1 hr or until failure.

Test drive for first hour South on I-25. Straight shot down front range Denver to Colorado Springs. AHC responded well, damping comfort to sport felt good. No real curves to test dampening, but all seems normal and good.

Until I pulled off the HWY. As I brake AHC failed. I had to drive in failsafe about 5 minutes until I could pull over and hook up Tech stream. I expected to see fluid temp high. But 5 minutes with OAT of 60F overcast (no sun) and lite mist. It may have cold fast. Road angle, had Front end lower than rear of vehicle a little.

AHC in L flashing OFF
DTC C1736 again.
IMG_6541.JPEG

IMG_6542.JPEG


Shut down engine, sat key off (IG SW OFF) a minute or so. Started and system working normal again.
Drove a bit and system failed again.
OAT 47F overcast light rain Denver to Colo Springs.
 
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Continued:
Let sit ~1 hour AHC system back to normal. Went and grab lunch for 1 hour or so. Dove back North I-25 for and hour. System failed again getting off HWY about 1 hour later driving time.

Now front lower than rear w/AHC flashing OFF in"N"
IMG_6546.JPEG

IMG_6547.JPEG


I did get working again, but just very intermittent and short duration. I noted; It seems AHC dash height indicator, sometimes changed from N to L or L to N, while AHC OFF flashing. Which was dependent on, if front end higher or lower than rear (direction parked on ~8% grade or ~4% on the road)
Voltage at IG & +B seems normal, when system working. But really did watch close. Just noticing this condition. They may just be indicating, system in failsafe.
Anytime working, if I go into active test mod. System fails instantly, when I attempt to activate any of the allowed activation test. Why?
Could it be a gate value issue.
While working I'd get +10 graduations. Indicating globes good. But could one be bad. But why going over bumps, did I not feel a bad one.
Could Accumulator be failing. Up down time seemed normal. But really need to test again to make sure. Up would be accumulator indicator.
Failure anytime I was looking, happen above 91F.
Fails more prevalent after active use of up and down, then braking. Braking is a sensor for AHC, signalling to dampen, so font doesn't dip.

I tried:
1/4 LH wire housing block plug out & in
Battery disconnect 24 hr.
Driving.
Plugging in 3 used sensors (2 front 1 rear). Did see indication of this, in tech steam. But no change in system heights.
Washing undercarriage.
Disconnecting hot lead to AMP.
Disconnecting all 3 wire blocks at pump. This is when C1718 presser sensor is new, not clearing.
Active test, +B voltage jumps to 7 or 8 Voltx, than drops back slowly (5 sec.) to ~1or 2V
T-bar 3CW LH & RH. LH now at max.
Basically all things that seem to get working before.

If AHC CPU, relays, fuses or sensors. Wouldn't bad be bad all the time.
Same hold question of Globes? and Accumulator?

Today I'll start by CW RH T-bar. See if that helps, by taking pressure off AHC yet again. Nothing left on LH.
Since pressure found previously going up, and T-bar now max on LH. I would think failed globe(s). But why would AHC work well when it does work?
Could it be a fail accumulator (rare). But if so, why does/did it seem to go up without issue when working? I really need to check up time, but must get working again to do so.

Then I'll begin at beginning again

I'll also say after getting system up and running back in Dec 2021. I did have reservation. After failure and pressure changing and needing CW readjusting. That and unplug and plug rear 1/4 wire harness had results early on. So much so I recommended we wait and see how system performs, before adding Kings or air bags. As will be getting loaded at times with dirt bikes, hitch mount rack.
 
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The problem obviously sounds electrical, as you allude to, and your interest in the +B voltage makes sense from that standpoint. something seems to be telling the AHC ECU there isn’t enough voltage to run things properly. Indro’s post suggests you need to be at 10-16V.
Agree totally with this assessment. Your additional info on the intermittent nature suggests electrical as well. I’m pretty sure that when the ECUs report a voltage they are measuring the voltage internal to the ECU. Since the +B is obviously out of range, I would start by getting a volt meter and connecting the probe as close as possible to the ECU +B pin. If the voltage is low there then consult the EWD and trace the wiring backwards to find the fault. If the +B is ok at the ECU that would point to a bad ECU, which would be puzzling since you seem to have ruled that out already. Anyway, not sure I’ve really added much beyond what @LndXrsr said above, but the +B low voltage really looks like the place to start.
 
Probably you have already done this, but for completeness suggest check and test battery and charging system – the method probably is well-known to you but also see description at

LC100 Workshop Manual - https://lc100e.github.io/

then the following further tabs:

Engine Repair Manual [2UZ-FE] > CHARGING > CHARGING SYSTEM (Page CH1 or Page CH2 depending on Model Year)

Anyway, assuming that the charging system is in good order and returning to your screenshots ….

I don’t understand what causes the Techstream message “Lost Communication with the vehicle” but maybe that is not particularly relevant.

The first screenshot -- shows one unidentified DTC – temperature is -22degF, so this DTC would be due to temperature sensor being disconnected, otherwise all values look normal in all respects, including IG 13. 7 volts and +B 14.1 volts. Interesting -- don’t recall seeing +B greater than IG on other AHC screenshots on IH8MUD – but maybe I have not been observant enough and/or maybe that just represents a fully charged battery in good condition? Or does it suggest a alternator/regulator on the way out?

The second screenshot – shows no DTC’s, temperature 100degF seems reasonable, all other values look reasonable in all respects, including IG 13. 7 volts and +B 12.9 volts – with +B is 0.8 volts lower than IG and also +B is 1.2 volts less than +B in the first screenshot.

These IG and +B voltages on the second screenshot do not seem unusual to me and are consistent with most other screenshots I have seen on IH8MUD over recent years. My own most recent results (DEC ’21) with vehicle operating normally with new batteries (two in parallel in 1HD-FTE) and new OEM replacement Toyota/Denso 27060-17230 alternator (long story!) were:

IG 14.0 volts and +B 13.2 volts
IG 13.8 volts and +B 12.9 volts

The third screenshot is a puzzle. It shows one unidentified DTC, not temperature sensor this time, temperature is high at 129degF suggesting pump has been working hard (?), height sensors are all high but closely grouped within 0.3 inches of each other, Front and Rear AHC pressures are somewhat high – maybe corresponding to height of vehicle (?), Main Relay Expectation is “OFF” (?) but “ON” on previous screenshots, IG 12.1 volts (low), +B 1.7 volts (extremely low).

Ordinarily, this would raise suspicions about an under-charged battery as would expect to see around 13 volts on the distribution system from the battery. Assuming the charging system is healthy, that would suggest checking the 15Amp AHC-B fuse and the 20Amp AHC-IG fuse (both in the junction box behind the kickboard on the LHS of the LHD driver’s footwell) and also checking the operation of the AHC Main Relay (which is mounted on the AHC ECU under the dashboard.

In theory
, nothing is going to happen, including “Active Test”, in the AHC/TEMS systems if these items are preventing delivery of electrical power.

However, in practice the third screenshot also shows that the vehicle has been raised with reasonable although somewhat high Front and Rear AHC pressures and normal Height Control Accumulator pressure. This did not happen without the operation of the AHC system – or are these readings old readings which have not been cleared from the ECU??

The third screenshot shows a DTC – has it been possible to identify this DTC?

The ECU response to disable AHC (and initiate protective ‘fail-safe functions) could happen in 0.5 seconds or 2 seconds (if C1743 depending on circumstances), or in 0.6 seconds (if C1762).

So apologies @2001LC – I don’t get what has happened in the circumstances depicted in the the third screenshot. As a Iate edit I have wondered if the vehicle is still capable of being raised by the AHC system-- perhaps slowly compared to expectation -- then a possibility might be a partially blocked AHC Pump -- but that does not fit with the voltage readings which suggest that neither the AHC circuit nor the AHC Pump is receiving electrical power. There must be a better answer -- I think I am missing something.

Hopefully other IH8MUD Members can be more helpful! Maybe @Rebus Knebus or @YvesNL given some of their previous posts on similar topics??

As well as the charging reference given far above, I have had a look at the following references:

LC100 Workshop Manual - https://lc100e.github.io/ (This is an LC100 FSM but should be good enough for LX470 purposes).

then follow these tabs in the menu on LHS of opening page:

Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS

then the following further tabs:

Power Source Circuit (Page DI-294) – with engine running, need battery voltage (+B) of 10 volts to 16 volts, and, ECU terminal voltage (IG) of 9 volts to 14 volts – to enable operation of AHC Pump & Motor and Damping Force Control Actuators (TEMS). If not, check/test the circuit as described, including AHC-IG fuse (behind LHS cover in LHS footwell) and continuity of harness and connectors back to ECU. [Note: These voltages only define what the AHC ECU would accept -- see the first reference far above for the necessary voltage specifications for a healthy Charging System].

also

Tc Terminal Circuit (Page DI-306) – check/test correct voltage is present at terminals DLC3 socket under dash used for Techstream (otherwise Techstream will not operate correctly).

also

Ts Terminal Circuit (Page DI-308) – further check/test correct voltage is present terminals at DLC3 socket under dash used for Techstream (otherwise Techstream will not operate correctly).

then

C1741 – AHC Motor Relay Circuit (Page DI-243) -- check/test whether the relay is working – if not, no power to AHC Pump, ‘fail-safe function’ occurs as described, and there is no AHC/TEMS operation.

and especially

C1743 – AHC Main Relay Circuit (Page DI-248) -- check/test whether the relay (mounted on ECU) is working – if not, no power is supplied to the ECU or any part of the AHC system, ‘fail-safe function’ occurs as described (note the three different conditions, 1 or 2 or 3 which are difficult to understand!) -- response times are 0.5 seconds or 2 seconds (depending on circumstances), then there is no AHC/TEMS operation including “Active Test”.

C1762 – Fluid Pressure Abnormality -- Pump & Motor Does Not Supply Fluid (Page 256) – check/test circuit, note that the response time is very quick ~0.6 seconds to protect pump -- and then there is no AHC/TEMS operation including “Active Test”.

Like your note on lubing the adjuster arms. I may look into doing that.

The problem obviously sounds electrical, as you allude to, and your interest in the +B voltage makes sense from that standpoint. something seems to be telling the AHC ECU there isn’t enough voltage to run things properly. Indro’s post suggests you need to be at 10-16V.

To clarify, you have checked the relays Indro mentioned above?

If so, this seems like an ECU (which you’ve said you ruled out) or a random wire near the ECU or pump that is frayed, intermittently shorting, etc. and resulting in the low +B voltage reading at the ECU (I assume this is where the voltage is read). This car’s history of electrical hemline is not encouraging. It may take a very careful combing of the wires to ensure things are all intact.

Agree totally with this assessment. Your additional info on the intermittent nature suggests electrical as well. I’m pretty sure that when the ECUs report a voltage they are measuring the voltage internal to the ECU. Since the +B is obviously out of range, I would start by getting a volt meter and connecting the probe as close as possible to the ECU +B pin. If the voltage is low there then consult the EWD and trace the wiring backwards to find the fault. If the +B is ok at the ECU that would point to a bad ECU, which would be puzzling since you seem to have ruled that out already. Anyway, not sure I’ve really added much beyond what @LndXrsr said above, but the +B low voltage really looks like the place to start.
Thank you guys for the help, especially you @IndroCruise for taking so much time.

I've been going through diagnostics. Everything testing to spec, so far. But:
"pressure sensor test" . I've issue with FSM "Voltage: Approx. 4.5V." Issue being I'm seeing ~0.65V when applying 4.5V. Which indicates NG.

But I've 2 used pumps w/pressure sensor. Each a different year type. Which one matches the one on the 01LX, I'm working on. In that wire harness housing block connect of sensor is a triangle shape. The other matches the diagram in FSM. Which is inline type connector.

In all I get about ~0.65v -+0.02.
These other two on the bench, are from working AHC take-offs from conversion to LC typ suspension. So no reason, to think bad.

Anyone know if I'm misreading FSM or is FSM wrong?
IMG_6891.JPEG
 
EDIT: see my next post. I think I found the something simple we were missing…


Sounds like you’re doing it right: apply voltage to 3 and 1, measure voltage at 2 and 1. You’re applying it to the sensor itself and not the connector from the harness, yes?

No idea why all 3 systems you have would read like that. Something’s amiss, but it doesn’t seem to be your technique unless there’s something very simple we’re missing.
 
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Just looked through my diagnostics files. The 2000.8+ models with the triangle connector show different values: 1.48-1.85V with the car running. Try that!
 

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Just looked through my diagnostics files. The 2000.8+ models with the triangle connector show different values: 1.48-1.85V with the car running. Try that!
I did the pressure sensor voltage test for the triangle connector 2000.8+ models. I get 0.493 Volts, well below the 1.48-1.85V in FSM. But I was not surprise as system is in fail safe. But I swap in another triangle senor, and volts about the same at 0.487V.

I skipped the first test/inspection "suspension ECU test", but will come back to when I time.
 
MY IG voltage and B voltage are 7.7V / 7.4V

Occasionally my AHC suddenly works, I'm guessing the voltages are normal when it does sporadically work.

The three lights for L,M,H will flash on/off repeatedly, sometimes all three will turn off

I have replaced the 50 Amp fuse, relay next to the 50amp fuse, the 15 and 20 amp fuses, and the Relay by the computer. They all tested fine, but I replaced anyways incase they were behaving badly under load, I still have the same issues.

I replaced all three height sensors since once was bad and I'm at 300k miles

Does anyone have a diagram of what wire is what going into the AHC computer?

currently my front likes to get stuck low -2.5" and my rear is at a healthy height +0.5"
oil temp reads back at 135, but I never hear the pump trying to run, so that's very odd, might be reading high because voltage isn't at the right level
I've seen on some tech stream readings the Height control SW down/up/hold switch being ON when they aren't, I think this is some low voltage sorcery.

image_67190273.JPG


image_67196417.JPG
 
My first thought is a short, due to statements: "Occasionally my AHC suddenly works " and readings: " IG voltage and B voltage are 7.7V / 7.4V"

Second though, due to FL FR heights and oil temp high. You're carry to much weight on AHC system. By either having height sensors out of adjustment (sensor lift) or T-bars back off to much (CCW) or both.

To start with: I'd crank T-bar CW as far as possible, see is any improvement.
 
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Thanks for your response 2001LC,

I am leaning towards some kind of ground short since Vb and Vig are both low by the same amount.

The front of the vehicle is sitting very low and the rear is sitting at a good height, so I think the sensor readings are correct.

How can the oil temp be high if the pump never runs?

I managed to get it into high the other day just fine. I started the car, it immediately raised up to neutral, then I hit the up button and it immediately went into high. I would say the system works 1/50 days

I am concerned the TB might now be tightened up enough since I just had a guy rip everything out suspension, steering, bushing, bearing related and replaced it with Toyota parts. The AHC system was NOT working before this was done. It has not been functioning properly for over 3 years, but the vehicle has usually had enough lift to drive around comfortable. After getting the vehicle back, I replaced all 3 ride height sensors with Aisin brand sensors which should be Toyota.

I am leaning towards this being a wiring issue because the system initially went out when spring hit and temperatures outside got above freezing, maybe water causing an issue somewhere. I also had a very odd thing going on where turning on the passenger seat heater would cause the AHC lights to flicker on and off! This has gone away and no longer happens.




Anyways! I want to figure out where these Vb and Vig voltages come from or if the computer is creating them.

I have checked voltages at the fuses in the kick panel and at the main AHC relay while vehicle is operating and everything is 12+ volts. I replaced and tested the 50amp fuse and relay in the engine bay also for good measure.

I am planning on probing the ECU pins tomorrow and looking for anything broken or damaged underneath the vehicle.

Do you know where I could find correct voltage/resistance values for the 24 pin AHC ECU plug?

@2001LC , @suprarx7nut , @BullElk , @Moridinbg
 

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