Hydractive3+ any leeway to change reference height settings?

nickyg · Unread post by **nickyg** » 11 May 2010, 21:13

Hello all,

Just in follow up to a post I made in another thread, may I just ask any experts and those with greater knowledge than I (that's everyone here, then!) about the resetting of height values following a depressurisation, bleed, new LDS and repressurisation of the system on my C6 which I am now almost certain I require.

I see that the height values can be inputted ( to 6mm either way of a certain threshold?? not sure about this, but think that's right) through measuring at a certain point and performing a calculation against the wheel radius.

As I wish to ft my 20" wheels with summer tyres (8mm bigger diameter than standards ) when I finally get the chance to do the necessary with my hydraulics and LDS, my query is this:

Is there any leeway when inputting the reference heights?

I mean can I deliberately lower the front value in order to close the slighty odd front wheel arch gap, as on the C6 it is inexplicably larger than the rear arch gap, somewhat spoiling the aesthetics of a beautiful car...well it does when you are the owner and spend time being picky about your pride and joy!

Or would that value be critical in terms of ruining any suspension related calculations being performed by the ECU?

Thank you in advance for any insight, Nick

viorelovidiu · Unread post by **viorelovidiu** » 12 May 2010, 10:30

i`m interested too how we can adjust heigt references with lexia but on C5

i`ve replaced front height sensor and now my car stays a bit lower than before....

KariM1 · Unread post by **KariM1** » 12 May 2010, 19:41

Funny, I just today got angry on setting the reference heights on C5 H3+, and now came to see here for any hints.

I too installed larger rims, and now need to lower the car, being unorthodox or not. Lexia is not easy on this. It shows the set reference heights in steps (mine was 124/116 steps f/r), and gives you instructions how to measure the heights and formulas for calculating new reference heights. Then you input the calculated values in millimeters. If all goes well, new values are accepted, and now reference heights (in steps) on screen are somewhat different.

The difficulty is, that the calculated (by operator) heights h1m and h2m have to match to those what the suspension ecu has measured within some tolerance, and lexia does not tell you the accepted limits nor what suspension ecu thinks h1m/h2m are (in millimeters)! If you exceed the tolerance, the references are reseted to default (128/120 on my C5). Getting the car on the instructed height is relatively easy if the height sensors are mechanically pre-adjusted correctly (read the instructions in Service). But when you try to lie to the car about the measured height, you have to make several minor changes toward your goal, while the car is constantly changing the height and making guessing the wanted input even harder... With many moments of iterarion I ended at 119/112, so it's a bit lower than before, but not what I had thought.

I found Lexia quite difficult on this. Is there any easier method for setting the car parametrically on desired height? I'd not like to go for mechanical adjustment.

nickyg · Unread post by **nickyg** » 12 May 2010, 23:52

From what I have gathered I believed there was a max adjustment of 6mm plus or minus from a predefined rigid value. On my C6 I think It's something similar to your figures of just above 120 front/ just below 120 rear. Interesting that someone else is looking at this solution!

Though what you have said has given me pause for thought in that I assumed that these figures simply represented millimetres, and the measurements manually taken would correspond somewhat with these figures.

Are you saying that these values are simply some sort of arbitrary ratio? This seems a mad way of doing things by Citroen, as millemetres and centimetres acts as perfectly serviceable and simple increments in all other aspects of our lives!!

On the flip side, a value of plus or minus 6 (from what I have read) would seem more useful if it was a stepped interval larger than a millemetre, as adjustment by 6mm seems almost pointless.

Mate, are you entirely sure that what we are proposing, ie: "lying" to the car regarding our true height measurements taken as per the the guidelines, has no bearing on the subsequent damping related calculations that are performed by the ECU?

I'm hoping that it is indeed irrelevant and could simply act as a workaround solution to alter the aesthetic look of the wheels in their arches and with all calculations simply performed the same only occuring 1-6mm lower/ higher than before (or whatever the min/max window for adjustments are).

Cheers!

Nick

KariM1 · Unread post by **KariM1** » 13 May 2010, 11:27

nickyg wrote: Are you saying that these values are simply some sort of arbitrary ratio?

Well, not arbitrary. To me the shown "step"-values seem as decimal presentation of 8-bit analog-to-digital conversion raw values. 8-bit conversion would give scale 0 to 255 in discrete steps. I assume the height sensor is a pontentiometer (in old C5 H3+, not sure about "wheel travel sensor" in C6), and ecu reads it via AD conversion. The default values at around 128 would nicely be at around the center of the available scale.

One sure thing is that the values, which are input to lexia by the operator, are definitely not the same as what it displays as results of reference height step-values. After measurements and calculations (in millimeters), the accepted input values were around 140/060 in my case, and these resulted in somewhere close to 120/120 step values.

Ability to set the preference height parametrically seems to be a way of fine tuning. As said in Service document B3BE0CP0 (for C5 X3 break H3+), the mechanical pre-adjustment needs to be performed when the heights measured are not within the tolerance of the heights calculated (± 10 mm) .

And now to the part when we are trying to alter the reference height against the instructions given by the manufacturer:

After my previous message I remembered that current height (in steps) is shown in suspension parameter page in lexia. Now I can make a linear table of measured->calculated heights versus the step-values shown in lexia. Then, when trying to give new values inside the allowed tolerance, I can check current height in parameter page (in steps), crossreference a new mm-value in my table, and alter it a bit (± 10 mm) prior inputing.

Changing the reference height from original brings the car lower (or higher) than it thinks it is. Being reasonable with the changes, I think the suspension geometry is not destroyed, but fact is that is closer to the bumb stops, and may bottom out more easily. In normal situation H3+ may switch to firmer mode before bottoming, but if we "lie" the reference height, it may switch to firm mode too late on big road undulations.

Please note: I don't know how my findings apply on C6, as it's H3+ seems much more refined than the ancient system in old C5 inheriting mechanically from XM. For example, there seems to be no need for mechanical pre-adjustment of the height sensors in C6. They should have renamed the newer version to H4+ or something... And you are correct, the tolerance is ±6mm in C6.

nickyg · Unread post by **nickyg** » 13 May 2010, 23:25

Yes, there does seem to be some differences, though there are many similarities too.

I haven't invested in a Lexia as of yet, so am none the wiser as to what step values appear when the metric calculations are input.

What are your base figures in millimetres? I see you have posted some figures you have input in your C5: 140/060 (140mm, and is this 60mm or just a typo?). You have +/- 10mm, I note the C6 is indeed +/- 6mm only.

There is just under 20mm difference between the front wheel arch gaps and the rear wheel arch gaps on my C6, which has been exacerbated by a further 8-9mm on the front passenger side as I believe that the wheel travel sensor/height sensor must have been disturbed as there was a driveshaft put in that side.

Surely this must be the cause of the extra 8-9mm, I'm thinking.

As regards the standard, and slightly odd looking, 20mm wheel arch difference front to back, I'm really hoping I can get this brought down a little via this unorthodox Lexia method.

I have documentation seeming to stating that the base figures and tolerances of input are:
Front- 160mm +/-6mm
Rear- 111mm +/-6mm

In a best case scenario, I could close the gap 12mm, I suppose.

Clogzz · Unread post by **Clogzz** » 14 May 2010, 12:11

For in case it might be relevant, I’ve read a story like that if an LDS drainage causes air to get into the high pressure pipes, the system can only be re-pressurised by pumping 0.5 Bar of air into the top of the LDS tank after refilling.
It would have to do with the C5 and C6 pipes being very thin and causing air lock.

Picture of a pressurisation contraption to fit the spare tyre:
http://img76.imageshack.us/img76/4759/t ... iongv8.jpg

fred1 · Unread post by **fred1** » 14 May 2010, 17:52

Hi,

Not sure why you would need to adjust the height setting after changing the fluid.

On C5 the height corrector is a potentiometer linked the antiroll bar (front or back). There is a small ball joint mounted on a rotatable bracket/clamp on the AR and a similar one on the pot and a link arm.

The suspension ECU has a resistance value set point that corresponds to the centre position of the pot. When the height changes the pot resistabce changes and the ECU compares its set point with the pot reading and makes an adjustment to move the suspension to return the pot to its centre point and thus its reading to be tha same as the ECU set poiny.

You can change the set height in two ways:-

i) change the ECU set point value

ii) move the clamp/ball joint position on the AR bar.

If you don't mess with either the height should return to the same point after draining/refilling the fluid.

John

dnsey · Unread post by **dnsey** » 14 May 2010, 19:20

I can't see any reason why the height couldn't be altered simply by 'padding' the hieght sensor potentiometers - i.e. adding a little more resistance to the appropriate side of the circuit. This could, of course, itself take the form of a pot, so that the height could be trimmed from within the cabin if desired.
This says nothing about the implications for overall geometry, of course.

nickyg · Unread post by **nickyg** » 14 May 2010, 19:57

fred1 wrote:Hi,

Not sure why you would need to adjust the height setting after changing the fluid.

On C5 the height corrector is a potentiometer linked the antiroll bar (front or back). There is a small ball joint mounted on a rotatable bracket/clamp on the AR and a similar one on the pot and a link arm.

The suspension ECU has a resistance value set point that corresponds to the centre position of the pot. When the height changes the pot resistabce changes and the ECU compares its set point with the pot reading and makes an adjustment to move the suspension to return the pot to its centre point and thus its reading to be tha same as the ECU set poiny.

You can change the set height in two ways:-

i) change the ECU set point value

ii) move the clamp/ball joint position on the AR bar.

If you don't mess with either the height should return to the same point after draining/refilling the fluid.

John

It's not really linked to the draining procedure per say, more that a garage has raised and lowered the car several times without following the proper, important prerequisites (eg: removing LDS cap), and has also probably disturbed my passenger "wheel travel sensor"/height sensor (referred to as the former on my C6) as there is now a further height discrepancy on that wheel where a new driveshaft went in.

I'm not 100% sure but my best guess is that air has thus been introduced and I have also wept/lost a little LDS during those many forced and incorrectly performed raising and lowerings.

I was a tad unhappy with the slightly odd looking 15-20mm difference in the front wheel arch gaps as opposed to the rear even before this saga, so am trying to get the whole package cleared up together, I suppose!

DickieG · Unread post by **DickieG** » 14 May 2010, 20:27

Not entirely sure if this applies to a C6 (should work on a C5) surely the easiest way is to undo/adjust the clamp on the anti-roll bar, no need for a computer, just ramps and a spanner.

nickyg · Unread post by **nickyg** » 14 May 2010, 21:17

Well, for a C6 it may not be as easy as that, as there are sensors on each corner, rather than centrally located on the antiroll bar. I'm by no means an expert, but am trying to learn as much as I can here.. and I think that the C6 potentiometers/height sensors might be a slightly different beast (though I hope not) as there doesn't seem to be scope for a physical, mechanical adjustment.

I say this as the service manual states that even an identified deviation in the mounting bracket of the sensor will necessitate replacement of said bracket.

I'm assuming this to mean that the sensor must be held in quite a specific position, thus negating the contingency for mechanical adjustment.

KariM1 · Unread post by **KariM1** » 15 May 2010, 15:02

nickyg wrote: What are your base figures in millimetres? I see you have posted some figures you have input in your C5: 140/060 (140mm, and is this 60mm or just a typo?). You have +/- 10mm, I note the C6 is indeed +/- 6mm only.

I can't now recall the formulas. They were given by lexia upon configuring the reference height. It included measuring wheel radius and height from ground on specific reference points on front and rear subframes. Yes, those values 140mm and 60mm (when inputing, it was neccessary to give three digits, thus 060) were results of one measurement/calculation run. They are not universal for C5, as the car changes the height and new measurements have to be made every time the reference height is to be configured.

nickyg · Unread post by **nickyg** » 15 May 2010, 19:12

I have went back and re-read, for the C6 the scope is:

K1 and K2 (Fronts): 160mm (+/-6mm)
K3 and K4 (Rears): 111mm (+/-6mm)

Yes it does, say mm after the 160 and 111, as these values may get confused with the step values mentioned by Kari earlier. He explains it well as being the value representing a marraige of the measured value in mm and the analogue output of the potentiometer.

When inputting reference heights the instructions are to take a measurement from the points Citroen define. Four points that are obviously always constant and unmoving in relation to one another... unless one was to have a badly warped chassis!

This value is then subtracted from the radius of the wheel resulting in the final value, this is called K1M, K2M etc according to the wheel. (though the values above are annotated without the M, I'm assuming they are the same thing).

If I'm reading this correctly it means that the measurements taken, when subtracted from the wheel radius can never be less than 154mm and 105mm or greater than 166mm and 117mm.

I've actually had a wee look around my front potentiometers, as they are very easy to see to the fore of the wheels, beside the driveshaft. Close enough to easily become disturbed when removing and refitting a shaft, infact!!

I now see the possibility of performing a variation on the suggestion a few posts back by DickieG.

Were the sensor mounting bracket to become slightly deformed (by accident or design!) or shimmed by a hair up in a way that would trick the suspension into believing it was slightly higher than it is, that may work, though I wouldn't want to play with this by any more than a few mil. The end result would be a closing of wheel arch gap slightly.

In effect, the reverse of what has probably happened to me, my sensor on passenger front wheel likely thinks it is a few millimetres lower than what it truly is because of being disturbed, resulting in higher wheel arch gap on that wheel.

Most sensible course of action is probably get two new mounting brackets and/or potentiometers, for the fronts, fit and forget (I'll know those elements are as true as can be then) and perform the reference adjustment and steal as many millemetres as possible in Lexia.

Cheers, Nick