Rear end is too low with AHC in good health. What are the causes?

[yuji]

Hey guys,

So I believe the reason my EMS exhaust rubs the driveshaft is because my rear end is too low.

Check this out:

Based on a majority of pics I see online... the rear should not be this low. Right?

Now the question is... what is the fix?

Given the AHC, my understanding is that the system will raise the rear until the correct height (or die trying) regardless of how worn the springs are. The neutral pressures will be up, but they will lift regardless until they die.

I can still put it in High and the AHC graduation test passes, so I'm guessing that's not the problem.

Can anything other than sensor position lower the rear end?

Here's where my sensor is: looks unmoved.

Zoomed in:

I don't want to just raise this IF there is another cause outside of this sensor position.

Thanks all!

 

[hankinid]

I think I'd start by checking the height sensor.

If that checks ok and you know your AHC functions ok, that leaves you with replacing the rear coils. More than a few to select from past oem.

More than a few posts about air bags as an adjunct to the springs...

Maybe something in the faq's?

hth

Steve

 

[yuji]

I think I'd start by checking the height sensor.

If that checks ok and you know your AHC functions ok, that leaves you with replacing the rear coils. More than a few to select from past oem.

More than a few posts about air bags as an adjunct to the springs...

Maybe something in the faq's?

hth

Steve

Hey Steve, so that's what I wanted to confirm: i'm pretty sure even if the coils are too weak, the AHC should be compensating with extra pressure to keep things level. Being able to raise further via going to High confirms that AHC is completely capable of lifting the vehicle (so it's not maxing out AHC pressure).

Kinda like how adjusting torsion bars on an AHC won't do anything to the height.

I will take the Front and Back specced measurements shortly.. also wanted to confirm that the back is definitely too low even visually.

 

[hankinid]

Hey Steve, so that's what I wanted to confirm: i'm pretty sure even if the coils are too weak, the AHC should be compensating with extra pressure to keep things level. Being able to raise further via going to High confirms that AHC is completely capable of lifting the vehicle (so it's not maxing out AHC pressure).

Kinda like how adjusting torsion bars on an AHC won't do anything to the height.

I will take the Front and Back specced measurements shortly.. also wanted to confirm that the back is definitely too low even visually.

Assuming height sensor works ok, ahc will try to compensate height...owners manual notes ahc can cover a load of up to 700 lbs. (people, dogs, stuff, gas, etc.) and obviously that includes the springs doing their job correctly. As springs weaken (if that is your issue) ahc may try to compensate more which may put a strain on the height control system.

I do not know if ahc will limit itself automatically, or if it continues to pump if springs are in fact weak.

Check the heights on front and back per the fsm no load in the truck, make adjustments to baseline the height (if you can). At that point might be interesting to have a dealer measure pressures, or pickup the TechScan program, grab a laptop and check it yourself.

Steve

 

[uHu]

yuji, your thinking is right.

There is probably something wrong with either the sensor or its linkage or wiring.
Would check linkage, movement, and position. Does the ahc adjust the car upwards when you move the adjuster upwards in its slot? (If you do this without a lift, drive on top of 4" blocks first, not to be squashed).

Could be that the sensor is faulty, that its electrical characteristics have changed because of wear or corrosion.

 

[yuji]

yuji, your thinking is right.

There is probably something wrong with either the sensor or its linkage or wiring.
Would check linkage, movement, and position. Does the ahc adjust the car upwards when you move the adjuster upwards in its slot? (If you do this without a lift, drive on top of 4" blocks first, not to be squashed).

Could be that the sensor is faulty, that its electrical characteristics have changed because of wear or corrosion.

Hey uHu thanks for the response! AHC gurus united!

I just moved the sensor up, and the rear did move up by about that much.
It now sits about 1.5 inches higher and I only rub over large speed bumps.


BAD LINKAGE:
So since it does move correctly, next up is the linkage?

I'm not sure what to look for here, but I presume the issue is that if the linkage seizes at the elbow partially or fully, that the sensor will read incorrect heights.

I will take off the adjuster nut and see if the linkage moves freely.


BAD WIRING:
After that, you suggested wiring: what am I looking for?


BAD SENSOR:
Have you heard of a busted sensor that reads relative readings correctly but the absolute number is off?

This part is a big magical.. there's this black box that's hard to debug.


Thanks for your !


Here's how it sits now... driveable / not afraid to leave the house.

 

[leej]

Yuji, did you ever get this resolved? I'm having similar problem.

Last week I noticed that the rear end on our LX seemed a little lower than normal (by about an inch or two, not terribly low, but when you really looked at it, you could tell it was lower), but the AHC still worked raising up and down (about 7 gradients on the reservoir). Then yesterday, the back end just seemed to drop. AHC still raises front fine, but nothing changes in the back (looks like the first picture in your post). Ride is extremely rough and rear end just seems to be sitting in the "low" mode???

I've read many of the AHC postings about accumulators, sagging coils, etc., but I'm still not sure what my specific problem is (and yes, I know one option is to switch out AHC for springs, but I would like to diagnose the AHC first). Any help would be appreciated

Thanks

Lee
2004 LX470 with AHC
2000 LC no AHC

 

[uHu]

There's plenty of info in the ahc threads in here. Have you checked sensor linkage, sensor values, pressures?

When you say 7 grad's, is that from Low to Hi? Anyhow, the number of grads will only be of value when pressures and heights (front, rear, Lo, Hi) are correct. But don't mix up globe condition and height adjustment - there is no connection between the two.

 

[ogjohnsmith]

My advice would be to get the Techstream software and cable and make sure your front and rear pressures are in check. If you don't and are over pressure your AHC system will eventually fail.

I leveled mine in the front, adjusted the torsion bars until front AHC pressures were back to factory spec. On the rear end I got new OEM springs installed at a Toyota dealer for $500 to bring the rear pressure back to spec. AHC should last another 100k miles now, I hope..

 

[leej]

Just to follow up and close the loop on my issues. Not sure if I have any "real" answers here (I didn't fix it myself), but hopefully my experience might help someone else.

The pump was working and would raise and lower the front, but the back was sitting way too low (seemed like it was bottomed out in the back, any small bump in the road was very harsh when the back went over). Then, while driving it to a local independent shop, the back raised up to normal again and seemed fine (in fact, I didn't notice it had raised until I got out and looked)?

The local shop said they thought one or more valves might be sticking. They said they took the valve system apart, and found some "junk" in it, so they cleaned everything and put in new AHC fluid, and everything has been working great for about 2 weeks now. I thought it might have just been the rear sensor, and when I asked about the rear sensor, they said they "rebuilt it" as well. When I asked what "rebuilt" meant on the sensor, they said it was really dirty and had a lot of "junk" in it, and so they cleaned it up and reassembled... Total bill was about $500 (5 hours of labor, plus the AHC fluid, plus tax etc.).

I'm wondering if it was simply the sensor (dirty or going bad), but things are working well now, and I'm happy for now. I thought the bill was a little high (without knowing exactly what they did), but I'm not sure I had the time or knowledge to diagnose and/or repair this on my on, and at least they didn't want to replace everything...

Hopefully the "repair" will last.

Lee
2004 LX470 with AHC (now working)
2000 LC