AHC Troubleshooting (Jarring/Harsh)

[UnstableOS]

Need to reach out to the community..
2005 Lx
92k Miles
All Maintenance performed on schedule

I've been through Lexus service (master tech) three times and he says " It's all operating within spec"

symptoms/Operation

1. Expansion cracks and short vertical bumps are very harsh under normal operating conditions.
2. Graduations are 10 (low to high)
3 Neutral pressure is unknown until Wed..
4. When operating with Height Control 'OFF' the suspension operates as expected under all conditions.
5. All base operations (Up/Down - Comfort/Sport) are functioning as expected
5. Fresh fluid

Any ideas? TIA

 

[kgrove]

I'm sure the first thing you'll hear is about neutral pressure... Will be good to see how yours tests out.

I'm going through exactly the same thing as you. The only difference is I've tested my neutral pressures and put them back in spec (adjusted torsion bars in front and replaced rear springs) and haven't tried operating wit the height control off... will try that soon. I haven't found the solution to mine yet and am still searching.

Out of curiosity - do your AHC settings (comfort vs sport) seem to make any material difference? Have you ever done anything - carrying heavy weight or tow a tongue heavy trailer - that overwhelmed the AHC making the truck run in L position?

 

[UnstableOS]

All settings from "Comfort" to "Sport" are noticeably different, but only when my HC is OFF. When I am default the suspension feels like a Model T

 

[PADDO]

All settings from "Comfort" to "Sport" are noticeably different, but only when my HC is OFF. When I am default the suspension feels like a Model T

Talk me through operating in OFF mode? Are you referring to damping performance at speeds <20mph (approx, can't recall exact speed). Unless you've installed an override or pulled fuses your system will turn on and default back to N and AHC will be active.

Sent from my iPhone using IH8MUD

 

[TXLX100]

Let us know what you find out. Mine (130k miles) is harsh over small bumps, with about 7 gradations, otherwise rides fine. I have kept the fluid changed out. I haven't checked the pressures yet, but plan to give it a go soon. I like being able to raise and lower the vehicle with getting my kids in and out, so going to try and keep it as long as it doesn't cost a bunch to fix it.

On a related note, does anyone know if slee sells used LC springs?

 

[PADDO]

Talk me through operating in OFF mode? Are you referring to damping performance at speeds <20mph (approx, can't recall exact speed). Unless you've installed an override or pulled fuses your system will turn on and default back to N and AHC will be active. Sent from my iPhone using IH8MUD

Half wrong, you can indeed drive in OFF, I was mistakenly thinking of how the system works if you raise or lower then turn it off and drive.

Sent from my iPhone using IH8MUD

 

[UnstableOS]

I am simply turning off the height control option and operating in N. When it is set to OFF, there is no raising or lowering of the system..

Even when HC is OFF the vehicle still lowers/raises to N at 20mph..again, all operations of the AHC are functioning.

 

[Lx470iH8Mud]

I was going to say that. I thought there was something wrong with mine. If turned off it automatically turns AHC back on by itself when I drive. So this is normal?

 

[UnstableOS]

I was going to say that. I thought there was something wrong with mine. If turned off it automatically turns AHC back on by itself when I drive. So this is normal?

When I turn off height control it stays off until I switch it back on and that includes restarts.

 

[rustydrummer]

I have a 2000 LX470 with 139,000 on the clock. Just got back from a 1,500 mile road trip... Truck ran great except that it is very harsh over bumps, especially at speed. My AHC seems to function fine, I have 9 graduations between H and L in the reservior. I noticed that when I go from H to L, the fluid in the reservior is foamy. The fluid is definitely old, as it is green and dirty. I know the newer fluid is red... Anyway, I thought I read somewhere that foamy fluid in the res could indicate rupture of the diaphragm in one or any of the accumulators. This truck is new to me and I am in the process of base lining fluids... I was just curious if it is worth trying to change the AHC fluid, or if it is a lost cause given the possibly bad accumulators. Opinions please, and thank you.

 

[Jack90210]

Anyway, I thought I read somewhere that foamy fluid in the res could indicate rupture of the diaphragm in one or any of the accumulators.

Good question, thank you for bringing it up. I just flushed my AHC fluid and took the moderately foamy fluid in the res as "normal." The ride in my '07 is good but not great; the fluid wasn't very dark (I am the 3rd owner, 2nd owner bought it 10k miles ago as a CPO) but it wasn't pink; high speed damping (sharp bumps) are softer but the vehicle still feels vague at speed to me (probably normal, that).

 

[rustydrummer]

Good question, thank you for bringing it up. I just flushed my AHC fluid and took the moderately foamy fluid in the res as "normal." The ride in my '07 is good but not great; the fluid wasn't very dark (I am the 3rd owner, 2nd owner bought it 10k miles ago as a CPO) but it wasn't pink; high speed damping (sharp bumps) are softer but the vehicle still feels vague at speed to me (probably normal, that).

So you did notice a difference in the ride after doing the flush? My fluid is definitely old and dirty... I guess I'll probably try flushing mine before I start tearing the suspension apart. Have you noticed if your fluid in the res is still foamy after the flush?

 

[UnstableOS]

OK, update on pressures

Front Neutral - 7.6
Rear Neutral - 6.5
Accumulator Press Sensor - 10.6

Lexus Master tech says there is nothing more they can do or recommend.. Ride still harsh intermittently and now even with the Height Control Off it has gotten worse.

 

[PADDO]

OK, update on pressures Front Neutral - 7.6 Rear Neutral - 6.5 Accumulator Press Sensor - 10.6 Lexus Master tech says there is nothing more they can do or recommend.. Ride still harsh intermittently and now even with the Height Control Off it has gotten worse.

3.5 turns cw on your TBs and 15mm trim packers in the rear will bring those pressures nicely into spec and hopefully you'll feel a noticeable improvement in you damping. Do the TB first and see how that feels. Don't forget that if you're running tire pressures significantly above factory 29/32 that will negatively impact ride quality too.

Sent from my iPhone using IH8MUD

 

[jOnathN]

So, per the manual, your pressure should be:
If measuring with Handheld Tester (e.g. TechStream)
Front pressure: 6.9 +/- 0.5 MPa (70 +/- 5 kgf/cm2 , 996 +/- 71 psi)
Rear pressure: 5.6 - 6.7 MPa (57 - 68 kgf/cm2 , 811 - 967 psi)
If measuring at the accumulator
Front pressure: 5.7 +/- 0.3 MPa (58 +/- 3 kgf/cm2 , 825 +/- 43 psi)
Rear pressure: 4.4 - 5.5 MPa (45 - 56 kgf/cm2 , 640 - 797 psi)

So yours are a little high but but probably not by much

 

[jOnathN]

If your problem really is intermittent that suggests that it is electrical. Maybe a bad ground somewhere or a bad selector switch?

In the off position the system would ignore the switch and most of the sensors. In the on position it would be trying to adjust...maybe something is shorted and pulling the damping actuators to max that gets cut out of the circuit when off. Could be one of the height sensors or the selector maybe is haywire.

I guess I would unplug, clean, and replug all of the sensors and switches. There aren't all that many.

 

[Jack90210]

So you did notice a difference in the ride after doing the flush? My fluid is definitely old and dirty... I guess I'll probably try flushing mine before I start tearing the suspension apart. Have you noticed if your fluid in the res is still foamy after the flush?

Sorry for the late response but I just noticed this. To clarify: ride quality is a bit better than it was before the flush; high-speed damping (sharp impacts) is less harsh than before, and the vehicle feels slightly more composed and less prone to wallowing in general. I should check for the foamy fluid.

 

[SWUtah]

Just a suggestion before you throw any $$ at you AHC with new parts look at replacing with a 2" OME lift. That is what I did love the outcome and no more AHC expense, plus you end up with a better looking tougher LX.

 

[rustydrummer]

Just a suggestion before you throw any $$ at you AHC with new parts look at replacing with a 2" OME lift. That is what I did love the outcome and no more AHC expense, plus you end up with a better looking tougher LX.

Yea, that was my plan when I bought it, I just didn't expect the AHC to crap out so soon. I've been spending $ getting everything baselined and running smooth, wasn't really planning on dropping $ on the lift yet, that's probably what I'll end up doing though. Good to hear that you are happy with your conversion.

 

[SWUtah]

Yea, that was my plan when I bought it, I just didn't expect the AHC to crap out so soon. I've been spending $ getting everything baselined and running smooth, wasn't really planning on dropping $ on the lift yet, that's probably what I'll end up doing though. Good to hear that you are happy with your conversion.

I don't know where you live but I drove from Las Vegas to Golden Colorado to have Slee Off-road do my OME with the Slee differential drop plus Slee rock slider steps. Could not be happier, plus Slee knows what they are doing so no problems. Funny what a difference 2"s can make