Seems like you do need to get the rear sensor back in the right spot so the car sits level. I wonder if it’s maybe the new tires you put on. If they are like E rated or very stiff off road tires that can affect the ride significantly. Otherwise I can’t see the dampening being unless the uneven level is telling the computer to stiffen up the dampening
LX570 AHC “Basics” - Added as sticky thread for AHC Issues
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Okay gonna try that in the morning. Worth a shot. They are C’s but I had Nitto Ridge Grapplers before, just on 20’s. I think those were XL rated, but I didn’t think it’d be that big of a difference. When the road is absolutely perfect it’s a lot smoother, just feels very tipsy and unplanted. Hard to explain, almost feels every wobbly and boat like. At first I thought the tires were perhaps unbalanced. But unbalanced tires usually showed up at high speeds for me in the past and shaky steering wheel, when this is kind of everywhere over 20. Thought maybe it’s misaligned but steering wheel is straight and it’s not pulling at all.
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Two changes - sensor lift and e tires, neither is good for ride.
The sensor lift you lose downtravel, and some e tires can be quite difficult to get to a safe and comfortable psi.
Fix the sensor lift and if you’re still riding rough you can point to the tires/rims.
xl is not E.
The sensor lift you lose downtravel, and some e tires can be quite difficult to get to a safe and comfortable psi.
Fix the sensor lift and if you’re still riding rough you can point to the tires/rims.
xl is not E.
For sure. C tires to just be clear. And only one sensor was lifted, just to clarify. But I mean this ride is unbearable. I’ve seen squatted Hondas that look more comfortable. I have heard E tires can be rough, which is why I didn’t go there. If this is C causing it alone, I can’t image what E would be like because it’d be dangerous to drive.
Might get a second opinion on tire balance
Do you have the old rims and tires to swap on?
I still have the original tires and rims yes.
Might consider swapping them on. It’s a drole way to spend two hours but if it rides good on the old tires like it used to, then you know it’s something with the new wheels set. And if not, it’s related to Ahc.
Definitely try to get your rear end back down. If it’s lifted you have limited droop as well as throwing the geometry of the rear pitman arm off. When lifted you get a lot more side to side movement when the suspension cycles. My butt-o-meter was very sensitive to this. Also, saw in the other thread you are at 42 PSI. Drop down to 35-37psi and try that out.
Okay perfect. Down normal suspension now. Didn’t get to try it out because of an appointment. And will drop down the PSI.
One thing I forgot on all this, though I’d be surprised if it made a terrible difference, but spare tire isn’t installed at all due to one rim coming in scuffed. So maybe it’s also a combo of a few things, rear seats removed, no spare, PSI, etc.
Posting here to hopefully help anyone who has a C1755 (Rear Gate Valve) code in the future. My LX570 first gave me the code in 2022 (as mentioned previously in this thread). I then had a pump failure, which I believe was unrelated. Sorted that out, but have intermittently had the C1755 code ever since. Sometimes it won’t pop up for several weeks, sometimes it won’t go away for a month or two. The AHC system is inoperable with the code present, and manually clearing it in Techstream doesn’t work, it comes right back.
I bought a used AHC ECU and swapped it in, and that didn’t change anything. I finally got out the multimeter and some long leads, and started doing the diagnostic tests in the FSM. First with both the N3 (height control valve) and K32 (AHC ECU) plugs disconnected I tested both ends of the harness and each pin was in spec (below 1 ohm) and the body grounds were fine as well.
Next step was to connect the N3 plug and test from the K32 end, and all pins were within spec at 3.8 ohms, except the K32-29 SLRG pin, which correlates with Rear Gate Valve. Since this test failed, the FSM suggested I replace the No. 1 Height Control Valve, which is mounted inside the frame rail near the rear passenger door. I tried cleaning the contacts on it, but it didn’t seem to help.
I found a new OEM part on ebay ($430 USD), and had my friend install it at his shop. When he had it apart he said my AHC lines were fairly rusty, and recommended I source replacements for peace of mind. I ordered replacements for all of the lines that connect to the Height Control Valve, he buttoned it up, and the system has been flawless ever since.
TLDR, if you have the C1755 code, test the K32 plug with the N3 plug connected, if pin K32-29 SLRG is out of spec, you likely need a new No. 1 Height Control Valve.
I bought a used AHC ECU and swapped it in, and that didn’t change anything. I finally got out the multimeter and some long leads, and started doing the diagnostic tests in the FSM. First with both the N3 (height control valve) and K32 (AHC ECU) plugs disconnected I tested both ends of the harness and each pin was in spec (below 1 ohm) and the body grounds were fine as well.
Next step was to connect the N3 plug and test from the K32 end, and all pins were within spec at 3.8 ohms, except the K32-29 SLRG pin, which correlates with Rear Gate Valve. Since this test failed, the FSM suggested I replace the No. 1 Height Control Valve, which is mounted inside the frame rail near the rear passenger door. I tried cleaning the contacts on it, but it didn’t seem to help.
I found a new OEM part on ebay ($430 USD), and had my friend install it at his shop. When he had it apart he said my AHC lines were fairly rusty, and recommended I source replacements for peace of mind. I ordered replacements for all of the lines that connect to the Height Control Valve, he buttoned it up, and the system has been flawless ever since.
TLDR, if you have the C1755 code, test the K32 plug with the N3 plug connected, if pin K32-29 SLRG is out of spec, you likely need a new No. 1 Height Control Valve.
It's time for another Fluid flush. I have an unopened can of fluid from my flush three years ago. Does anyone know if the fluid degrades in its original, unopened can? I hate tossing or wasting the stuff. Should I use it, or should I throw it away and buy more?
Hello all, my AHC pump went out, so I'm having a new one installed tomorrow (Lexus dealer in Vancouver, Canada).
The service guy I spoke to says they've been replacing several 200 series pumps recently, actually multiple times monthly is what he said... My pump on my 08 LX went out earlier this month, with only 206km (128k miles) on it.
Not sure why this is happening, perhaps just due to age? One of the other service guys there who also has a 2004 LX470 said the issues they're seeing are more on the 200 series, and not so much on the 100 series. His 100 series has 450+km on it with the original system and no issues. My last 470 also saw kms like that prior to having any issues...
I did my own fluid change last spring, but used factory fluid in the 2.5L tins (2) from the stealership.
After the full flush, I did top the reservoir up a bit higher than the amount that was in there earlier. Not a massive amount more, but a few extra graduations, just in case I did a sensor lift in the future (have not done this yet) I just wanted to make sure there was enough, and there was still plenty of room for excess fluid while in low mode.
Could that have caused it to go out early?
I'm scratching my head as to why that happened - my system/lines are not rusted out or anything. It's weird.
The service guy I spoke to says they've been replacing several 200 series pumps recently, actually multiple times monthly is what he said... My pump on my 08 LX went out earlier this month, with only 206km (128k miles) on it.
Not sure why this is happening, perhaps just due to age? One of the other service guys there who also has a 2004 LX470 said the issues they're seeing are more on the 200 series, and not so much on the 100 series. His 100 series has 450+km on it with the original system and no issues. My last 470 also saw kms like that prior to having any issues...
I did my own fluid change last spring, but used factory fluid in the 2.5L tins (2) from the stealership.
After the full flush, I did top the reservoir up a bit higher than the amount that was in there earlier. Not a massive amount more, but a few extra graduations, just in case I did a sensor lift in the future (have not done this yet) I just wanted to make sure there was enough, and there was still plenty of room for excess fluid while in low mode.
Could that have caused it to go out early?
I'm scratching my head as to why that happened - my system/lines are not rusted out or anything. It's weird.
Most common culprits based on gut feel and anecdotes
- Debris gets introduced because of silly reservoir design
- Air gets introduced and not bled out
- Age and or rust—first 570s have been on road since 2008
- There was a bad batch of fluid that would gel up and clog pump
I’m not too surprised. Stuff wears out eventually. I replaced the water pump recently, for example.
It’s a bummer as the design is not self priming and that complicates the replacement, otherwise the part itself isn’t too hard to remove and replace.
It’s a bummer as the design is not self priming and that complicates the replacement, otherwise the part itself isn’t too hard to remove and replace.
I have seen some people adjust the brackets when the vehicle is in N and some claim it should be adjusted when its in H?
Does it actually make any difference?
I understand you need to cycle the height settings several times after adjusting the brackets, drive it for a bit and see how it sits. Then readjust brackets to level front to back and side to side or fine tune with techstream?
Does it actually make any difference?
I understand you need to cycle the height settings several times after adjusting the brackets, drive it for a bit and see how it sits. Then readjust brackets to level front to back and side to side or fine tune with techstream?
I suspect people suggest high just to make access to the adjusters easier with wheels on.
I would definitely drive it a bit before you call your changes good.
Fine tuning is probably a misnomer. If you get things within a half inch of where you want to be. You are probably good. Especially if you aren’t going to use techstream to at least see what the sensor readings are.
Thanks! Service history shows Lexus did the AHC flush and top up less than 5k ago. Once sensor lift is complete I verify how its doing for AHC levels and top up if necessary.
wrong thread - please delete @Moderator
I fully raised my height sensors to fit slightly larger 285/60 Nittos. Toyota has never made it easy to run larger tires on the front
... I didn't notice any uneven wear on tires or driving difference. And just a one inch larger diameter tire makes a big difference. Would like to go bigger but I love the AHC function. But now this thread has me wondering if I should replace the fluid as a precaution at 72,000 miles.
