Definitive list of AHC maintenance items

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Nov 24, 2017
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Burbank, CA
Yes but the way I understand it, the L or H pressures readings don't translate into anything of value.
Only readings after going from L to N matter. In other words, start in L go to N & take that reading.
 
Joined
Jul 25, 2019
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144
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Yorktown, VA
Update: Today I was able to flush the fluid and adjust the height of the front end. The front is now at 20.25" center cap to fender on both sides. I will go back to the shop to continue trying to lower it tomorrow. I did my best to center the top nut in the slot and have equal length of the threaded rod on both sensors.

What has me concerned at the moment is the disparity in readings between the two front sensors. The driver's side is obviously new. Do they drift over time? Should they be replaced as a set?

I may be wrong but I believe the next step is to shorten the passenger side sensor, although I'm afraid it will lift the passenger side.
  • How do I get the two sensors closer to agreeing with each other?
    • Shorten the passenger side sensor until it reads closer to the driver side and then remove preload on the passenger side torsion bar?
    • Extend both sensors further and then increase the preload on the driver side torsion bar?

AHC N (17.49).png


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Joined
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Hungary - EU
I have the same issue:) interested to see your results. I’d say pick the one of the two and slide it in the slot until it agrees with the other one (engine off!). After that measure your height. If too high, adjust both accordingly. I think it’s somewhat normal that they’re are not sitting the same way in the UCA’s and for sure they do wear with time a bit and their resistances change.

That said I think the system averages the value of the two and sets the height based on that, but if they’re too far apart it’s easy to get the damping locked out (fail safe mode) - also, opposing to everything I’ve read - mine adjusts the lean a bit based on the sensors as well and not only the tbars. But something must be wrong with mine, acting the way no other is.

Remember, engine off every time you touch the suspension:)
 
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uHu

Shamowang
 
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Alright, got through all 30 pages. I have a much better understanding of the system but I could still use some advice with my truck. I picked up a 2003 LX with 148k miles. It has been in southeast Virginia its whole life and has very little rust. The AHC will go to L and N without an issue. When I select H it will blink a few times and then N will be lit solid. When the truck is in N the center cap to fender height is 21" all around. I got techstream working earlier and my pressures are all too high. My understanding of what I need to do is as follows:
  1. Check the accumulators by measuring the change in fluid level when going from L to N.
  2. Flush the system with new suspension fluid.
  3. Adjust height sensors to bring the front down to 19.75".
  4. Crank on the torsion bars to get the pressures down and reindex the torsion bars as necessary.
  5. Order either King or OEM + 30mm spacers for the rear.
Does my plan sound reasonable?
Would the pressures being off or sensors being maladjusted prevent it from getting into H?
Why does the passenger side height sensor seem to lag so much?
Yes, good plan. Except that the accumulator check wont be worth much until you have the pressures and heights right.

The extra height means that the pressure will be higher, unless it's been compensated for with stronger coils and adjusted torsion bars. The system can give only so much pressure, so when yours are too high it can't give you the extra pressure required to go into High. Get the height down and/or the springs adjusted/changed to get the pressures within specs; and you'll be able to go into High.

The imbalance in sensor reading L/R is either because you have a lean to the right (can be adjusted away with the TBs) or because one of the sensors is misadjusted. They should be less than 1/2" apart, typically 0.1 to 0.2.

If you need more height than standard, or have increased the rear weight, the Kings are better than spacers. If you want normal height and standard weight, the OE coils are good (Purple or Brown tho')

PS: Didn't see the page 2 before replying...
The front height is set as an average between the 2 sensors, and if the discrepancy is too big, it will give up. First check L/R physical height, and adjust it level with the TBs. Then adjust the sensors until you have the right physical height and equal height reading from the sensors. No tricks or threats. Plain sailing.

PS2: Don't be late on the brakes, we want the cruiser whole and healthy.
 
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hoser

SILVER Star
 
 
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Dec 21, 2003
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Bay Area, CA
Well, it finally happened.... '98 LX and first AHC issue after 21 years, 176k miles. While on a 2500 mile roadtrip, the AHC "off" light would blink occasionally and then one day, the front end dropped down to near the bumpstops. Pulled over, trying H-N-L modes and fiddling with the height sensors.... figuring there might be a dead spot around the "N" height of the sensor. After 10 minutes, the ride height went to normal! I was able to drive home 1000 miles with the AHC "Off" light blinking much of the time.

While home, ran the diagnostic codes... and Front, DS, height control sensor was showing error. I removed the sensor and opened it up to clean the contacts and spring but was not able to fix it. Internals didn't look too bad, except the corrosion or residue on one of the springs:

IMG_6250.jpeg


Ordered up both L & R front AHC sensors from two different vendors.
Aisin HST-020 ($100)
Aisin HST-021($150)

These are the OE parts for less than 1/2 the price if from Toyota. The actual sensor a la carte can be had for $25 from aftermarket vendors but I wanted OE and besides, my linkage/heim joints were looking kinda tired.

IMG_6257.jpeg


In the meantime, I disconnected the Front DS sensor and actually drove it around town for about 10 miles. The AHC "Off" light blinked the entire time but the vehicle height stayed normal! I thought this was interesting. So, if your front end drops, can you just disconnect the bad sensor and keep going on your merry way?

Today, I replaced both front sensor and all is normal, no error codes! :cool:
 
Joined
Jul 25, 2019
Messages
144
Location
Yorktown, VA
Well, it finally happened.... '98 LX and first AHC issue after 21 years, 176k miles. While on a 2500 mile roadtrip, the AHC "off" light would blink occasionally and then one day, the front end dropped down to near the bumpstops. Pulled over, trying H-N-L modes and fiddling with the height sensors.... figuring there might be a dead spot around the "N" height of the sensor. After 10 minutes, the ride height went to normal! I was able to drive home 1000 miles with the AHC "Off" light blinking much of the time.

While home, ran the diagnostic codes... and Front, DS, height control sensor was showing error. I removed the sensor and opened it up to clean the contacts and spring but was not able to fix it. Internals didn't look too bad, except the corrosion or residue on one of the springs:

Ordered up both L & R front AHC sensors from two different vendors.
Aisin HST-020 ($100)
Aisin HST-021($150)

These are the OE parts for less than 1/2 the price if from Toyota. The actual sensor a la carte can be had for $25 from aftermarket vendors but I wanted OE and besides, my linkage/heim joints were looking kinda tired.

In the meantime, I disconnected the Front DS sensor and actually drove it around town for about 10 miles. The AHC "Off" light blinked the entire time but the vehicle height stayed normal! I thought this was interesting. So, if your front end drops, can you just disconnect the bad sensor and keep going on your merry way?

Today, I replaced both front sensor and all is normal, no error codes! :cool:
Nice. Which vendor did you buy from? AISIN is clearly visible on my sensor so I would not mind picking up a passenger side one from them. I have never purchased from Partssouq before but they have the lowest price ($182.57) I have seen for the OEM units.
Parts Souq - RH Height Sensor (89405-60012)
 
Joined
Jul 25, 2019
Messages
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Yorktown, VA
I am back to being thoroughly confused with the height sensors. Yesterday I was able to get the front height to 20.25" on both the driver and passenger side with the sensors almost fully lowered. There was a huge disparity between the height sensor readings in techstream so I decided to revisit it again today.

I cranked both the driver and passenger side torsion bar 10 turns each and now my pressures are much closer to where they should be.

To get the height sensors within 0.3" of each other I had to fully raise the driver side sensor and fully lower the passenger side sensor. I am completely out of room for adjustment and now the truck is sitting at 21.5" on both the driver and passenger side. I did not know how to proceed so I stopped messing with them.

I'm pretty sure I have given the truck the "AHC lift" with the position of the driver side sensor. I'm not sure I trust the passenger side sensor but it has not thrown an error.

Pressure - N (2019-08-10 12.07.00).png


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Joined
Jul 25, 2019
Messages
144
Location
Yorktown, VA
I'm pretty confident the passenger side sensor is bad. Or I'm doing something wrong. I don't know if the drivers side is bad enough to replace as well.

IMG_20190812_115638.jpg
 
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uHu

Shamowang
 
Joined
Nov 27, 2005
Messages
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Location
Oslo, Norway
There is your problem. Pin 2 to 3 is the overall sensor carbon trace resistance. Pin 1 is the moving slider. What you measure on 2-3 should always be equal to the sum of 1-3 plus 1-2, minus a little loss. (No values should be over 5 kOhm, and you have 500)

So you see that the overall resistance is approx equal on the two sensors, and the bad connection is on pin 1 on the PS sensor. Probably something similar to Hoser's pic above here.
 
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Joined
Jan 26, 2018
Messages
116
Location
Seattle
what do you mean the shocks shut off? @Sargy ???
View attachment 2018163

Update to my risky decision installing 80 series Dobinson springs in the back (standard height spring) on sensor lifted LX470. Driven 10k miles now.

The springs have taken a good amount of driving to settle and get to the same comfort levels that I am used to having. After a 300lb combined weight of of a Dissent rear bumper and spare tire, I still have amazing comfort with full AHC capabilities. Took a pressure reading and was excited to see how capable this setup can be in the future. 06 LX has nearly 200k miles, rear shocks replaced at 150k, all Globes and accumulator as well as front shocks are still original. 13 ticks on the graduation level.
View attachment 2018169

4.1 MPa-g! The shocks start to shut off partially at around half a tank of fuel, but the dampers continue give a good ride. Once filled up there is no problem. Its ready to take anything I throw in it!
 
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Joined
Jul 25, 2019
Messages
144
Location
Yorktown, VA
Update: I ordered the replacement passenger side height sensor just in case. Installed it earlier today and I am at 19.8" on the drivers side and 20.0" on the passenger side. Hopefully that is the end of my AHC problems for a while. Thanks to everyone for the help.

I disassembled the old sensor out of curiosity and was surprised at how clean it looked compared to others I have seen on the site. Upon closer inspection the middle spring looks like it is bent/shorter than the others and has some dirt/corrosion on the base of it. I am surprised it was enough of a problem to cause an issue though.

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2019-08-12 15.50.40.jpg
 
Joined
Jan 26, 2018
Messages
116
Location
Seattle
Yep. Are all of your AHC components stock?
I have a lil thread on this fyi PLEASE HELP AHC pogo stick

My globes are palides with about 2k miles on em and my rear springs have about 4k miles, my fluid is a wonderful clear red coming from all 5 bleeders and before this problem started everything was working perfectly with good heights level pressures ect graduation test is 14 and in H mode it works flawlessly

@BEG
 
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Joined
Nov 25, 2017
Messages
101
Location
Northern VA
I have a lil thread on this fyi PLEASE HELP AHC pogo stick

My globes are palides with about 2k miles on em and my rear springs have about 4k miles, my fluid is a wonderful clear red coming from all 5 bleeders and before this problem started everything was working perfectly with good heights level pressures ect graduation test is 14 and in H mode it works flawlessly

@BEG
I replied to that thread
 

uHu

Shamowang
 
Joined
Nov 27, 2005
Messages
1,900
Location
Oslo, Norway
....I disassembled the old sensor out of curiosity and was surprised at how clean it looked compared to others I have seen on the site. Upon closer inspection the middle spring looks like it is bent/shorter than the others and has some dirt/corrosion on the base of it. I am surprised it was enough of a problem to cause an issue though.
The problem with these sensors is the seal, or rather how the flat lid can't stand the pressure of the seal. The lid bends a bit between the screws, so that the seal gets too little pressure to keep humidity out. One way of sealing it better is to put a 5-6 mm aluminium plate on the outside of the lid, with 5 mm longer screws. The seal then makes a perfect fit all the way.
 
Joined
Jul 16, 2019
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Location
NOLA
  • How do I get the two sensors closer to agreeing with each other?
    • Shorten the passenger side sensor until it reads closer to the driver side and then remove preload on the passenger side torsion bar?
    • Extend both sensors further and then increase the preload on the driver side torsion bar?
I came looking for answers to a similar question, so maybe the answer to mine can help both of us. I had everything balanced L-R via TBs before I started adjusting height sensors. I had trouble getting the sensor to move within the adjustment slot, so I turned this nut thinking it would help:

2019-08-09 18.36.24.jpg


Not only did it not help, but my AHC quit and Techstream threw sensor malfunction DTCs for both front sensors. I noticed in the live data that the sensor values were way out of whack (-6" FL, +7" FR) and determined that I had screwed these settings up by twisting this nut. I adjusted these slowly while watching the live data to get them back into agreement. This resolved the DTCs and got the AHC working again. However while driving it around to try to get it into Low mode in preparation for a flush, I believe they got knocked back out of balance and the vehicle went into 'pogo' mode. So to my question: everything else being equal, is this an appropriate method to balance these height sensors? My next step unless told otherwise is to double check the linkage lengths and then further adjust these such that they are back to their original readings which were within 0.3" of one another. Thanks in advance for any input.
 
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