Hey guys! New 2000 LX470 (202k miles) owner here! I know this may be somewhere in the forums but I can’t seem to find it. I recently replaced lower control arms on the LX and the AHC is unable to go to high and feels bouncy now. I’ve read about the potential of a fluid flush or a bad accumulator but the AHC was working fine before the lower control arms were replaced. Is there something that needs to be adjusted? I’ve read about torsion bar and height sensor adjustments but just not sure which of the two, if any, I would need to do?
AHC won’t go to high and feels bouncy (1 Viewer)
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Start with basics. Connect to Techstream and read pressures and error codes.
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It shows no error codes but the heights and pressures seem a bit out of range. What do you think?
GTV
SILVER Star
Pressures are way out of spec. Start with a fluid flush and then get your pressures dialed in.
my pressure sensor readings dont go to 0 when i put it in Low - they stay the same as when they are in Neutral. any thoughts on what that could mean?
The pressure readings are only valid going up in height. The pressure going into low is erratic and I think completely unhelpful. The manual only deals with pressure specifications as you go from low up to neutral.
10.2 to 10.8 is generally the value of the accumulator. The accumulator is charged after the vehicle raises to whatever desired height you have. So depending on when the screenshot is taken, you may or may not see any pressure registering in techstream for the accumulator.
Front pressure is way off.
What others said, do a fluid change, check again and start with cranking the torsion bars.
What others said, do a fluid change, check again and start with cranking the torsion bars.
It has all been said in the above posts.
The video and “Cheat Sheet” provided by @suprarx7nut are great places to start.
To add some more detail comments:
Sensor readings per screenshot at your Post #3:
negative 18.2 millimetres -- Front Right Sensor
positive 3.4 millimetres -- Front Left Sensor
negative 0.6 millimetres -- Rear Sensor
Difference Front Right and Left = 14.8 millimetres
Difference Front Right and Rear = 17.6 millimetres
Looking for Sensor readings close to zero +/- 5 millimetres (+/- 0.2 inches).
Is this vehicle on a slope to the Right?
If yes, re-check Sensor readings on level ground,
If these ARE the Sensor readings taken on level ground (not in the street), then either
a. The vehicle has a lean, downwards to the Right (if so, correct by ‘cross-levelling’ the Front using torsion bar adjusters, not Height Control Sensor adjusters, engine OFF, equalising Right and Left hub-to-fender using a tape-measure), or,
b. Height Control Sensors are out of adjustment (if so, correct to zero +/- 5 millimetres at N height setting at preferred ‘ride height’ for the vehicle), or,
c. One or more Height Control Sensors are faulty (if so, check using FSM method or similar. Attempting to repair/refurbish a faulty Sensor is a mug’s game -- suggest replace faulty Sensor(s) with new OEM Sensors, avoid troublesome cheap fakes and avoid pre-owned Sensors unless tested).
Wide differences in Sensor readings can lead to the Suspension Electronic Control Unit (ECU) initiating ‘fail safe function’ in which Active Height Control (AHC) and Toyota Electronic Modulated Suspension (TEMS) are prohibited.
Alternatively, the difference may result in erratic or strange height behaviour, such as you describe.
The good news is that on your vehicle, AHC is still working, proven by the Techstream readings you have obtained, so the ‘fail safe function’ has not been applied by the ECU. This may indicate that the internal condition of the Sensors is OK, and perhaps a ‘lean’ or ‘slope’ is the issue -- but suggest always remain suspicious of aged Height Control Sensors.
By the way, for reasons explained in other posts, absence of Height Control Sensor DTC's on Techstream does not provide assurance that the Height Control Sensors and circuits are in good health. Inspection is insufficient, testing is necessary.
AHC pressure readings per screenshot at your Post #3:
12.4 Mpa -- Front AHC (FSM-specified range 6.4 MPa to 7.4 Mpa)
9.2 Mpa -- Rear AHC (FSM-specified range 5.6 Mpa to 6.7 Mpa )
10.8 Mpa -- Height Control Accumulator (commonly observed in the normal range 10.2 Mpa to 10.8 MPa) .
At these very high AHC Front and Rear pressures
If the ‘globes’ in this 23 years old, 202,000 miles vehicle are original, then they are well past their best and it is highly likely that a requirement for set of four (4) new ‘globes’ is in your near future – subject to testing as mentioned below.
Poor ‘globe’ condition will not be revealed by Techstream.
AHC pressures are governed by weight share between the mechanical suspension and the AHC system. Overall 'globe condition' has nothing to do with AHC pressures.
‘Globes’ in poor condition prevent effective damping and will result in very poor ‘ride comfort’.
If not seen before, definitely suggest also peruse this thread:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520
In summary, the correct sequence for AHC adjustment and ‘tuning’ is always the same order:
1. Check that vehicle vehicle is on level ground, wheels straight ahead, fuel full, no poorly distributed loads,
2. Check condition of Height Control Sensors – all should be close to zero +/- 5 millimetres or +/- 0.2 inches (AHC system cannot work correctly with faulty or incorrectly adjusted Height Control Sensors – absence of a DTC does not provide assurance of healthy Sensors),
3. Check/adjust/equalise Front ‘cross-level’ with torsion bar adjusters -- measured by tape-measure, engine and AHC “OFF”, then,
4. Check ‘ride heights’ at N height, measuring hub-to-fender by tape-measure – engine “OFF”, ignition “ON”, adjust if necessary using adjustment procedure and Height Sensor Control adjusters (not torsion bar adjusters), then,
5. Check AHC pressures by Techstream at N height after N > LO > N movement (allow 30 seconds after green AHC dashboard light stops blinking after arriving at N), then record Techstream results for Front, Rear, Height Control Accumulator, then,
6. If AHC pressures are out of the FSM-specified ranges, then (i) use Front torsion bar adjusters to vary share of Front vehicle weight carried by torsion bars and share of Front vehicle weight carried by Front AHC system, thereby adjusting Front AHC pressures, and, (ii) consider spacers or replacement/upgrade of Rear coil springs to vary share of Rear vehicle weight carried by springs and share of Rear vehicle weight carried by Rear AHC system, thereby adjusting Rear AHC pressures. (Note: Front AHC and Rear AHC are not hydraulically connected but changing the Front and Rear weight distributions may cause some small interactions between Front and Rear AHC pressures and some ‘fine tuning’ may be required), then,
7. When heights and AHC Front AHC and Rear AHC pressures are correct, check overall ‘globe’ condition by observing the difference in AHC Fluid level at AHC Tank between H and LO heights. Per FSM, difference of around 14 graduations means ‘globes’ are near new; when the difference has declined to around 7 graduations, replace all four (4) ‘globes’. Results of this test at incorrect AHC pressures are not comparable with FSM numbers.
The video and “Cheat Sheet” provided by @suprarx7nut are great places to start.
To add some more detail comments:
Sensor readings per screenshot at your Post #3:
negative 18.2 millimetres -- Front Right Sensor
positive 3.4 millimetres -- Front Left Sensor
negative 0.6 millimetres -- Rear Sensor
Difference Front Right and Left = 14.8 millimetres
Difference Front Right and Rear = 17.6 millimetres
Looking for Sensor readings close to zero +/- 5 millimetres (+/- 0.2 inches).
Is this vehicle on a slope to the Right?
If yes, re-check Sensor readings on level ground,
If these ARE the Sensor readings taken on level ground (not in the street), then either
a. The vehicle has a lean, downwards to the Right (if so, correct by ‘cross-levelling’ the Front using torsion bar adjusters, not Height Control Sensor adjusters, engine OFF, equalising Right and Left hub-to-fender using a tape-measure), or,
b. Height Control Sensors are out of adjustment (if so, correct to zero +/- 5 millimetres at N height setting at preferred ‘ride height’ for the vehicle), or,
c. One or more Height Control Sensors are faulty (if so, check using FSM method or similar. Attempting to repair/refurbish a faulty Sensor is a mug’s game -- suggest replace faulty Sensor(s) with new OEM Sensors, avoid troublesome cheap fakes and avoid pre-owned Sensors unless tested).
Wide differences in Sensor readings can lead to the Suspension Electronic Control Unit (ECU) initiating ‘fail safe function’ in which Active Height Control (AHC) and Toyota Electronic Modulated Suspension (TEMS) are prohibited.
Alternatively, the difference may result in erratic or strange height behaviour, such as you describe.
The good news is that on your vehicle, AHC is still working, proven by the Techstream readings you have obtained, so the ‘fail safe function’ has not been applied by the ECU. This may indicate that the internal condition of the Sensors is OK, and perhaps a ‘lean’ or ‘slope’ is the issue -- but suggest always remain suspicious of aged Height Control Sensors.
By the way, for reasons explained in other posts, absence of Height Control Sensor DTC's on Techstream does not provide assurance that the Height Control Sensors and circuits are in good health. Inspection is insufficient, testing is necessary.
AHC pressure readings per screenshot at your Post #3:
12.4 Mpa -- Front AHC (FSM-specified range 6.4 MPa to 7.4 Mpa)
9.2 Mpa -- Rear AHC (FSM-specified range 5.6 Mpa to 6.7 Mpa )
10.8 Mpa -- Height Control Accumulator (commonly observed in the normal range 10.2 Mpa to 10.8 MPa) .
At these very high AHC Front and Rear pressures
- damping is severely compromised and ‘ride comfort’ is guaranteed to be rough and springy, and,
- if left in this condition, there is a high risk of challenging the seals in the ‘shock absorbers’ and elsewhere, resulting in leaks and possible permanent damage.
If the ‘globes’ in this 23 years old, 202,000 miles vehicle are original, then they are well past their best and it is highly likely that a requirement for set of four (4) new ‘globes’ is in your near future – subject to testing as mentioned below.
Poor ‘globe’ condition will not be revealed by Techstream.
AHC pressures are governed by weight share between the mechanical suspension and the AHC system. Overall 'globe condition' has nothing to do with AHC pressures.
‘Globes’ in poor condition prevent effective damping and will result in very poor ‘ride comfort’.
If not seen before, definitely suggest also peruse this thread:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520
In summary, the correct sequence for AHC adjustment and ‘tuning’ is always the same order:
1. Check that vehicle vehicle is on level ground, wheels straight ahead, fuel full, no poorly distributed loads,
2. Check condition of Height Control Sensors – all should be close to zero +/- 5 millimetres or +/- 0.2 inches (AHC system cannot work correctly with faulty or incorrectly adjusted Height Control Sensors – absence of a DTC does not provide assurance of healthy Sensors),
3. Check/adjust/equalise Front ‘cross-level’ with torsion bar adjusters -- measured by tape-measure, engine and AHC “OFF”, then,
4. Check ‘ride heights’ at N height, measuring hub-to-fender by tape-measure – engine “OFF”, ignition “ON”, adjust if necessary using adjustment procedure and Height Sensor Control adjusters (not torsion bar adjusters), then,
5. Check AHC pressures by Techstream at N height after N > LO > N movement (allow 30 seconds after green AHC dashboard light stops blinking after arriving at N), then record Techstream results for Front, Rear, Height Control Accumulator, then,
6. If AHC pressures are out of the FSM-specified ranges, then (i) use Front torsion bar adjusters to vary share of Front vehicle weight carried by torsion bars and share of Front vehicle weight carried by Front AHC system, thereby adjusting Front AHC pressures, and, (ii) consider spacers or replacement/upgrade of Rear coil springs to vary share of Rear vehicle weight carried by springs and share of Rear vehicle weight carried by Rear AHC system, thereby adjusting Rear AHC pressures. (Note: Front AHC and Rear AHC are not hydraulically connected but changing the Front and Rear weight distributions may cause some small interactions between Front and Rear AHC pressures and some ‘fine tuning’ may be required), then,
7. When heights and AHC Front AHC and Rear AHC pressures are correct, check overall ‘globe’ condition by observing the difference in AHC Fluid level at AHC Tank between H and LO heights. Per FSM, difference of around 14 graduations means ‘globes’ are near new; when the difference has declined to around 7 graduations, replace all four (4) ‘globes’. Results of this test at incorrect AHC pressures are not comparable with FSM numbers.
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Not a problem.
When "Oil Temperature Sensor (OTS) unplugged". OTS reading will be -22F (-30c) (not register), and the Accumulator Senor will read 0.0 (not register). Your screen shot show 13c, so your OTS is plugged in, which is why you have Accu. 10.8Mpa.
When T-bars reset during assembly of LCA R&R, they where not adjusted properly (to loose). Start by measuring side to side heights. Than Cross Level by tuning 30mm adjuster bolt of T-bar, clock-wise on the low side. The LH (DS) will always be turned in more (less thread remaining) than RH (PS), as your full fuel tank (more weight) is on DS side.
Tip: Turn/Adjust T-bar bolts when AHC in H. Or jack-up front end. This drops LCA, taking weight off T-bars, making turning T-bar adjuster bolt much easier.
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just did a fluid flush and it's a huge difference in ride quality - im no longer scared of speed bumps!
however, i still have a lingering problem (same as before fluid flush) of the rear raising and lowering continually while the truck is in neutral, in park, with the engine running. when i put it in park, the rear drops about 1/2in, and a couple seconds later, it raises itself back up, then repeats ad infinitum. even if the ground is not totally level, it shouldn't keep resetting like that so im not sure what is going on. any thoughts?
however, i still have a lingering problem (same as before fluid flush) of the rear raising and lowering continually while the truck is in neutral, in park, with the engine running. when i put it in park, the rear drops about 1/2in, and a couple seconds later, it raises itself back up, then repeats ad infinitum. even if the ground is not totally level, it shouldn't keep resetting like that so im not sure what is going on. any thoughts?
lol it was still very good info! thank you!
LOL Not so well said. As I was responding to OP issue after LCA R&R and your (AtoypA) Mpg readings, as one in vehicle.
You do need to go through, what IndroCruise has laid-out for you. Also, it may be very helpful if you layout what has been done on your rig (yr & mileage), it's configuration (heights, Mpa, stock or built, AHC adjustment, etc.). Also, perhaps be a little more descriptive of why "speed bumps scared you"!
havent got around to unplugging the temp sensor yet, but here's the reading i took after the fluid flush. also, sidenote: i had C1762 "Abnormal Oil Pressure for Pump" code, which i cleared bc i figured the pump was not used to having this much fluid? my reservoir was damn near empty before the flush and i never would've even checked it but the truck wouldnt go into high and that led me down the ahc rabbit hole.
come to think of it... could that be the reason it's always trying to level itself back and forth? could there be air in the system from when i tried to put it in high and there wasn't enough fluid?
come to think of it... could that be the reason it's always trying to level itself back and forth? could there be air in the system from when i tried to put it in high and there wasn't enough fluid?
oh haha speed bumps have always scared me bc the suspension (on current truck and previous one) always felt like it was breaking if i went over speedbump at anything other than idle speed!
..... such as hub-to-fender height measurements all round, not just screenshot without physical details, any reason for very large steering reading, total weight of vehicle and all in it or on it when travelling,
Any likely issues with FSM guidance on weight?
How close to standard are raise times and heights compared to FSM guidance?
Now that AHC pressures are reasonable, how does the overall condition of 'globes' look using the difference in graduations between HI and LO heights, compared with FSM numbers at specified pressures?
Are the 'globes' on the vehicle original on this 2000 LX470 with ~202,000 miles? If not, how old are the 'globes'?
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In a stock LX, properly set up suspension. I can hit speed bumps & dips at most any speed, and they glide over bumps (Feel is smooth in comfort, little stiffer in sport).
I did have one, felt like no suspension over the bumps. It have a failed globe and for some unknown reason. Shock are near impossible to compressor or extend by hand (off vehicle). I suspect a non Toyota AHC fluid had been used, at some time in its history.
interestinggggg... i hope my ahc is salvageable! i do have ~9 graduations L-to-H so i'm hoping that means my globes are in good shape. im glad i can put in H now, but just need to figure out this faulty leveling thing. maybe it's a sign one of the rear globes is bad?
So, still no details on weights nor hub-to-fender heights nor times? The points are that if heights are unusually high at N, obviously they will be higher at HI, also AHC pressure increases with height and spring/torsion bar share of vehicle weight reduces -- if AHC pressures are approaching the limit, this will result in slow raise times, reluctance to raise to HI, and also likelihood of slipping back to N, worse when striking a bump. More or less ditto with weight.
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