XM Hydractive 2 stuck in sport mode.

[howzat]

My problem is that my XM (1998 vintage) is in sport suspension mode all the time. As it has comfort spheres the ride is acceptable but I would like to get it working properly. Following advice from various sources I opened up the computer to see if the mosfets were burnt out. They looked fine however and when I did the door opening check they gave the correct output to the output socket of the computer.

When I checked the plug on the electrovalve however I did not get correct output. I did however get a brief pulse after the door was closed indicating that the wiring was intact.

What I need is a circuit diag. with wire colour codes or advice from those who have similar problems. Its all a bit beyond the haynes manual.
Any suggestions gratefully accepted!

Howzat

[Peter.N.]

I would have said look at 'club XM', its a mine of information, but unfortunatly its down at the moment. If your centre spheres are u/s it will give you those symptoms, but I assume you have changed those as well.

I have comfort spheres on mine, feels almost like a CX except for a roughish ride over broken surfaces at low speed, but I think that's down to the tyres.

[NiSk]

I assume you know that the electrovalve is activated by a short 12 V pulse and then maintained in (open) state by a square wave. So if you are measuring with anything other than an oscilliscope or spectrum analyser you probably won't see anything.

//NiSk

[AndersDK]

And to conclude the electrovalve issue : the coil has a built-in snubber diode. This is known to shortcircuit.
mandrake will be happy to dig up his thread on that issue.

However I tend to agree with NiSk : have a go on the centre spheres.

[Mandrake]

My problem is that my XM (1998 vintage) is in sport suspension mode all the time. As it has comfort spheres the ride is acceptable but I would like to get it working properly. Following advice from various sources I opened up the computer to see if the mosfets were burnt out. They looked fine however and when I did the door opening check they gave the correct output to the output socket of the computer.

When I checked the plug on the electrovalve however I did not get correct output. I did however get a brief pulse after the door was closed indicating that the wiring was intact.

Did you unplug the plug to the electrovalve when you did this test ? If so you'll only see a short pulse because the computer measures the load drawn by the electrovalve, and it will detect a fault condition and turn off the power to both electrovalves for one minute. (Then pulse it on again briefly to see if the fault has gone)

Therefore you MUST measure the voltage while the electrovalves are still both connected. (Easy enough if you stab the active wire with a sharp pin)

As others have mentioned it supplies 12v for half a second, and then switches to a pulse waveform with an RMS of about 3v thereafter. The pulse rate is only 1Khz so any decent digital meter should be able to measure it. (Failing that connect an LED with a 100 ohm resistor)

What I need is a circuit diag. with wire colour codes or advice from those who have similar problems. Its all a bit beyond the haynes manual.
Any suggestions gratefully accepted!

Howzat

Well theres really only 3 things that can cause the car to seem to be in hard mode all the time - centre spheres dead flat/punctured, faulty electrovalves, or missing voltage to the electrovalves.

Pinouts of the Hydractive 2 computer are available, although I don't have a link handy at the moment...

Theres LOTS of information about the Hydractive 2 system on this forum already if you manage to find it as the search function isn't that good...(I often can't find some of my own posts which I KNOW are on here somewhere )

Regards,
Simon

[deian]

Hi,

A malfuntioning Hydractive ECU will make it ride in hard mode too, as will lack of voltage to the Hydractive ECU... check that it gets a healthy feed of at least 12v (preferably about 14V with the engine running).

Hope it helps.

[howzat]

Thank you all for your suggestions which are very helpful. It did dawn on me that I should not check it with the plug disconnected. I will connect my storage scope so that I can see what is happening. Can anyone tell me what sort of difference one should expect between sport and normal. This is one of the later cars regd early 1999. Perhaps the fact that I have fitted comfort spheres makes the difference less noticeable.

Thanks

Howzat

[deian]

sport and normal ridewise?... or when u press the switch, well the button just makes the system more sensitive, as for soft and hard i can't say as i don't think my car ride correctly at the moment

[Mandrake]

Thank you all for your suggestions which are very helpful. It did dawn on me that I should not check it with the plug disconnected. I will connect my storage scope so that I can see what is happening. Can anyone tell me what sort of difference one should expect between sport and normal. This is one of the later cars regd early 1999. Perhaps the fact that I have fitted comfort spheres makes the difference less noticeable.

Thanks

Howzat

Do you mean what the difference is in the electrical signal or in the ride characteristics ?

If the former, then first we need to clear up the difference between hard/soft modes, and normal/sport.

Hard and soft modes are the actual physical modes of the suspension -

In hard mode the electrovalves are both OFF, which causes the centre spheres to be isolated, and also isolates left and right sides from each other.

With only the strut spheres in operation with very stiff damper valves you get a firm ride, and the blocking of left/right oil flow further reduces roll. If you have comfort spheres fitted hard mode wont be as hard as it otherwise might be....

Soft mode is when the electrovalves are both energized - they get pulsed with 12v for half a second when switching state which is necessary to kick them into action, then get held on with a 3v RMS PWM waveform to reduce power dissipation. (With 12v they would overheat and burn out in a few minutes)

Soft mode connects the middle sphere to both sides through two damper valves in the block the sphere is attached to. This also connects left and right via the two damper valves... the result is much softer ride but more roll flexibility. (Good for ride on uneven roads, not so good for cornering...)

Then we have the normal/sport modes on the console switch -

All this does is influence the decision making of the computer, it does NOT directly switch the hard and soft modes. In either switch setting the suspension will ALWAYS be in soft mode if you are cruising along in a straight line with no cornerning or accelerating/braking on a smooth piece of road.

And it will ALWAYS be in hard mode if you are cornering/braking/accelerating vigorously. What the switch changes is the thresholds that trigger a change from soft to hard. (And also the time delays before returning to soft)

Just as one example sport mode requires less steering wheel angle at a given speed than normal mode to trigger the hard mode, and will stay in hard mode a bit longer after you straighten up. (There are literally dozens of other decisions it affects)

So the switch is basically a driving style choice - do you want a comfortable ride as much as possible, or do you want flatter cornering and tighter handling ?

I find the normal mode fine for 90% of driving, you get a good ride most of the time but if you start pushing it around the corners it firms it up just at the right time to keep the car under control...

I find the sport mode can be fun to use on smooth windy country roads, but in normal around town driving it just switches to hard too often, as the throttle sensor becomes hyperactive in sport mode, with the slightest movement sending it into hard mode...

A really good read on the Hydractive 2 system (which is what your late model XM will have - same as the Xantia) can be found here:

http://www.tramontana.co.hu/citroen/guide/guide.php

It should explain everything you want to know about how it works.

Regards,
Simon