Factory AHC Sensor Position

Joined
Jul 31, 2006
Messages
263
Location
Denver, CO.
Had one of my Volvo techs put new upper control arms in my 05 LX, he didn’t note the position of the front sensor heim in the slotted boss on the old arm prior to removal. He placed the sensor all the way at the bottom of the slot on the new arms, which locked out the high setting and rode like garbage.
My question is, is the sensor supposed to be all the way at the top of the slotted section per factory settings? I moved both up about 3/4 of the way, now the high setting works and it rides better, but it still seems a bit higher than before in “N.”

Thanks for your help,

Brad
 

GTV

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Jan 31, 2019
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Where Crosstreks aren’t
It’s supposed to be roughly in the middle. Putting it towards the top will raise the front, the bottom will lower it.

Read your pressures and adjust the torsion bars accordingly and the ride quality will improve regardless of suspension height.
 
Joined
Aug 5, 2019
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Acampo, CA
I just ordered a new set and yes, they seem to be right in the middle.

5A568598-0B69-4454-8055-2115F1295819.jpeg
 
Joined
Jul 31, 2006
Messages
263
Location
Denver, CO.
Thank you, I am actually only referring to the heim that fastens to the upper arm. No adjustments were made to the stud portion of the adjuster, which does appear to be set roughly in the middle as in the picture above. Moving the stud up and tightening definitely improved the ride and seemed to lower the front a bit. I’m just not sure if there is a default setting or factory guidance as to where it should be.
We are replacing all of the AHC ram bushings and accumulators next week, I’ll have my Toyota guys monitor and adjust pressures once that and the associated flush are complete. I just had to get the control arms in for my wife asap and my Toyota stores were too far away!
Thanks as always for any help and insight, I appreciate it so much!
C8F1B985-4816-4D76-B081-52921670874F.jpeg
 
Joined
Jul 31, 2006
Messages
263
Location
Denver, CO.
Also, that’s just a picture I stole from the web, not my LX as the positions are different from mine.
 

GTV

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Messages
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Location
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If you’re just trying to get to factory ride height the positions of the sensors are irrelevant as long as the height and the pressures are correct.

 
Joined
Dec 6, 2016
Messages
705
Location
Brisbane, Australia
Had one of my Volvo techs put new upper control arms in my 05 LX, he didn’t note the position of the front sensor heim in the slotted boss on the old arm prior to removal. He placed the sensor all the way at the bottom of the slot on the new arms, which locked out the high setting and rode like garbage.
My question is, is the sensor supposed to be all the way at the top of the slotted section per factory settings? I moved both up about 3/4 of the way, now the high setting works and it rides better, but it still seems a bit higher than before in “N.”

Thanks for your help,

Brad

There are no "factory settings" nor 'right' or 'wrong' positions for the slotted adjusters for the Height Control Sensors .... because they are meant to be 'adjustable'.

It is an 'inside story' -- all about getting the brushes to the right position on the carbon track inside a healthy Height Control Sensor to send the correct signal to the Suspension Electronic Control Unit (ECU), matching the desired "N" height setting on the centre console.

Taking the story from the top ....

The pic below shows what the Right Hand Side Front Height Control Sensor should look like "out of the box". There is a temporary plastic post which holds the Sensor in the factory-set mid-swing position at which it sends the correct signal (2.25 volts) to the Suspension Electronic Control Unit corresponding to "N" height setting.

Techstream (or other scanner) does not report this voltage but instead translates it into a reading in inches (or millimetres). At "N" height this reading should be zero +/- 0.2 inches or zero +/- 5 millimetres which appears on the Techstream or scanner screen..

At the factory, the Sensor is attached to the vehicle with the temporary plastic post intact, and with the vehicle sitting at the FSM-specified physical height.

The attaching bolt then will land in the slider wherever it does -- some variability in the position of the bolt in the slider is expected between different vehicles because there always will be some manufacturing tolerances in the manufacture of the chassis and body and in the fitting of suspension components.

After installation, this plastic post is meant to break on the first movement of the Upper Control Arm and thereafter becomes irrelevant.

The vehicle is now factory-set to self-level automatically to "N" height. The Suspension Electronic Control Unit (ECU) causes the vehicle to raise or lower until the Sensor returns to this position and sends the correct signal for "N" height to the ECU. This is exactly the designed purpose of Active Height Control (AHC) -- this is what it is meant to do continuously when the vehicle is driven, unless there is a fault or an overload condition.

The ability to choose "LO" or "HI" heights at the centre console (subject to load and speed limits) is an added feature. No separate adjustments are available for "LO" and "HI" settings -- that is set by the firmware inside the ECU and which seems to be a tightly held Toyota/Lexus secret!!

After the pictures, fast-forward to what happens when original Sensors must be adjusted or replaced.

AHC - RHS Front Height Control Sensor with N pin.jpg


AHC - Height Control Sensor Explanation.jpg



When adjusting or replacing Height Control Sensors .....

The first thing to do is ensure that the Sensor is healthy -- this means removing the Sensor, dismantling and inspecting, and performing the FSM-prescribed test, or at least checking that the Sensor resistance varies in a smooth linear manner as suggested by @PADDO in the link far below.

Beware -- absence of DTC's C1711, C1712, C1713 does not provide assurance that a Sensor is healthy! It simply means that the signal is within the FSM-specified range (0.3 volts to 4.7 volts) but does not indicate whether the actual signal is correct for the set height position.

A fault with brushes or the carbon track or effects of moisture ingress, corrosion or whatever may still allow an acceptable voltage signal from the Sensor within the the required range (so no DTC) but cause an incorrect signal for the height of the vehicle and result in aberrant effects.

There are multiple stories on IH8MUD about AHC difficulties and strange vehicle behaviour which come down to faulty Height Control Sensor(s) even though no DTC is given. These Sensors are simple, robust, longlife items -- but they are 'wear items'. Original Sensors have been operating in the tough underbody environment for at least 15 years (2007 vehicles) or maybe up to 24 years (1998 vehicles) and eventually need replacement.

Assuming healthy Height Control Sensors ....

The next thing to do is to cross-level the tape-measured front physical heights of the vehicle using only the torsion bar adjusters as described in the first attachment. If this step is omitted, confusion will follow. It does not matter what the heights are in this preliminary step -- they just need to be equalised, Front Left and Front Right. The Rear will set itself -- if it does not, it indicates other problems in vehicle geometry which need to be explored, leave it for now.

With cross-levelling done, the next step is to set the vehicle height. Few people use the very finnicky, hard-to-measure FSM height specifications. Instead the approximations of hub-to-fender tape-measurements of 19.75 inches (or 500millimetres) at Front both sides, and, 20.50 inches (or 520 millimetres) at the Rear both sides, have been found to be good enough for most purposes for a stock vehicle. This approximation assumes no chassis or body damage nor unusual wear-and-tear of suspension components, control arms, axles, ball-joints etc.

However, these nominated heights are not essential -- it is up to the Owner to decide on the chosen operating heights (or ride heights) of his/her vehicle, within the allowable limits of the suspension geometry and drivelines.

More height means increased AHC pressures (and vice versa) and that would have to be compensated later.

Note that different to a conventional suspension, the vehicle front operating height (also called the ride height) is not set using the torsion bar adjusters.

Perhaps the simplest way to set to the tape-measured physical operating heights of the vehicle is to use the "Active Test" via Techstream, or, use the "Active Test" method at Section 5 at page 6 in the second attachment (using an unbent paperclip in place of SST 09843-18020 connector), and in that way set the vehicle at the desired Front and Rear tape-measured heights.

Then with physical Front and Rear heights now set to where you want them to be when returning to "N" height setting at any time, turn the engine "OFF", and leave the vehicle at the desired heights. Turn ignition "ON" (but not the engine) with Techstream (or other scanner) connected so that the Height Control Sensor readings are visible on the Techstream screen.

Adjust the Sensor position per FSM recommendation in the extract below, preferably using the slider bolt (the double-ended heim bolt can be used but this is very fiddly) until the Sensor reading on Techstream (or other scanner) is zero +/- 0.2 inches or zero +/- 5 millimetres.

Job done -- almost!

With vehicle operating height (or ride height) set, it is now important to check both Front and Rear AHC pressures -- and adjust them to be within (and preferably at the lower end of) the FSM-specified ranges. At the Front, this requires turning both torsion bar adjusters in the same direction to transfer weight from (or sometimes to) the AHC system to achieve the required pressures -- adjust with engine "OFF" to avoid activating the AHC system while doing this work, then start engine with AHC "ON" to take actual AHC pressure readings after making "N">"LO">"N" height movements in the usual way. Some height change might be noticed while actually turning the torsion bar adjusters -- this will be overridden by the AHC system when it operates, so allow a little time after starting engine, and check all measurements and fine-tune all adjustments after driving the vehicle.

See further insights provided by longtime AHC guru @PADDO ) at Post #2 at this link:



AHC Sensor Adjustment.jpg
 

Attachments

  • AHC - Cross level per FSM LoRes.pdf
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  • AHC suspension precheck and damper check.pdf
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