Citroen XM Hydractive Speed Sensor Location

[AlperAkbilgi]

Hello,

Does anyone know the location of the hydractive speed sensor? It always shows zero on my car and hydractive doesn't switch to hard mode.

[Mandrake]

Not sure if its the same on the XM but on the Xantia the same road speed sensor mounted on the gearbox drives the speedo and also supplies the cruise control ECU and the hydractive ECU - they're all wired in parallel to the same sensor.

So if your speedo works and cruise control (if fitted) works that would narrow it down to the Hydractive ECU or the wiring to it.

[AlperAkbilgi]

Not sure if its the same on the XM but on the Xantia the same road speed sensor mounted on the gearbox drives the speedo and also supplies the cruise control ECU and the hydractive ECU - they're all wired in parallel to the same sensor.

So if your speedo works and cruise control (if fitted) works that would narrow it down to the Hydractive ECU or the wiring to it.

My speedo works fine and I don't have cruise control. I guess, Ihave to check the wirings. Thanks a lot.

[CitroJim]

Depends on the XM. An S1 or S1.5 with a cable driven speedo has the speed sensor located half-way up the speedo cable by the bulkhead...

Here's a picture to show where it is..



S2 XMs with an electronic speedo are where Mandrake says... Same as the Xantia...

Hydractive faults can be caused by all sorts of problems but are easily solved usually. In the case of the XM though two very distinct breeds were fitted (Hydractive I or Hydractive II) and many details differences therein. To diagnose further we need the RP number of the XM in question...

Just as an aside, I've seen several older XMs now where the electrovalves have been permanently wired to 12v to keep them in soft mode permanently. This may be the problem with yours. Can you see any butchery around the Hydractive ECU to suggest this?

[AlperAkbilgi]

Depends on the XM. An S1 or S1.5 with a cable driven speedo has the speed sensor located half-way up the speedo cable by the bulkhead...

Here's a picture to show where it is..



S2 XMs with an electronic speedo are where Mandrake says... Same as the Xantia...

Hydractive faults can be caused by all sorts of problems but are easily solved usually. In the case of the XM though two very distinct breeds were fitted (Hydractive I or Hydractive II) and many details differences therein. To diagnose further we need the RP number of the XM in question...

Just as an aside, I've seen several older XMs now where the electrovalves have been permanently wired to 12v to keep them in soft mode permanently. This may be the problem with yours. Can you see any butchery around the Hydractive ECU to suggest this?

I have connected the car to lexia and saw that the hydractive control unit can't read the speed. it always shows zero. all other sensors are working just fine. there is no butchery around the Hydractive ECU. I have also checked the electrovalves and there is no modification to keep them in soft mode.

RPO: 6881
Last 8 of VIN: 00tt5623

[CitroJim]

OK, perfect that's an S2 with the later Hydractive II.

Is the speedo working?

[AlperAkbilgi]

OK, perfect that's an S2 with the later Hydractive II.

Is the speedo working?

Yes it works.

[CitroJim]

OK, perfect that's an S2 with the later Hydractive II.

Is the speedo working?

Yes it works.

OK, lovely. If you still have the Lexia then pop it on the engine ECU and see if that can see road speed. If it does and the speedo works then the sensor is OK. it's likely there will be a wiring fault up to the Hydractive ECU. You may need to break out the speed signal and pop an oscilloscope onto it to see what's going on.

Does the Hydractive properly switch to hard at rest with the ignition off 30s after closing the last door? You should hear the electrovalves hum whilst soft mode is in force and then the hum abruptly stop with a click 30s after closing the last door with ignition off as the ECU goes into hibernation. Opening any door even with the ignition off should wake the ECU and invoke soft mode (electrovalves humming). This confirms basic ECU operation.

Just after ignition off and before the ECU sleeps bounce each corner and things should be soft. keep bouncing with doors close and the ECU switches to hard before sleeping. You should feel the suspension harden up considerably. This tests electrovalves and the hydraulic aspects.

There is more to switching hard when on the move than just road speed. The ECU takes in speed, rate of change of acceleration/braking, steering wheel angle and rate of change of same and body roll. If a sensor input is missing a default will be used but the basic operation will continue although blunted a little in its response.

You don't feel the soft/hard switch - it is very fast and subtle but you really know it's working when you drive round corners with a bit of verve. For a comfy old barge the XM handles and corners remarkably well and all thanks to Hydractive.

If it really rolls and wallows into corners then the Hydractive is not working. If it's composed and nearly free of roll it is..

Hope that helps get to the bottom of this

Have you joined Club-XM yet? It's a good place

[AlperAkbilgi]

OK, perfect that's an S2 with the later Hydractive II.

Is the speedo working?

Yes it works.

OK, lovely. If you still have the Lexia then pop it on the engine ECU and see if that can see road speed. If it does and the speedo works then the sensor is OK. it's likely there will be a wiring fault up to the Hydractive ECU. You may need to break out the speed signal and pop an oscilloscope onto it to see what's going on.

Does the Hydractive properly switch to hard at rest with the ignition off 30s after closing the last door? You should hear the electrovalves hum whilst soft mode is in force and then the hum abruptly stop with a click 30s after closing the last door with ignition off as the ECU goes into hibernation. Opening any door even with the ignition off should wake the ECU and invoke soft mode (electrovalves humming). This confirms basic ECU operation.

Just after ignition off and before the ECU sleeps bounce each corner and things should be soft. keep bouncing with doors close and the ECU switches to hard before sleeping. You should feel the suspension harden up considerably. This tests electrovalves and the hydraulic aspects.

There is more to switching hard when on the move than just road speed. The ECU takes in speed, rate of change of acceleration/braking, steering wheel angle and rate of change of same and body roll. If a sensor input is missing a default will be used but the basic operation will continue although blunted a little in its response.

You don't feel the soft/hard switch - it is very fast and subtle but you really know it's working when you drive round corners with a bit of verve. For a comfy old barge the XM handles and corners remarkably well and all thanks to Hydractive.

If it really rolls and wallows into corners then the Hydractive is not working. If it's composed and nearly free of roll it is..

Hope that helps get to the bottom of this

Have you joined Club-XM yet? It's a good place

As an Activa owner I feel too much roll on my Xm, that is why I wanted to check the hydractive system to see if it is normal or not. I connected the lexia unit to the XM and gave the computer to my brother to tell me if the eloctrovalves operating or not. I push the car to the limits but it never switched to hard mode. I have switched on the spor mode button which is next to gear stick and got the same result.

Electrovalves closes after I lock the car. I can hear that. And the car stiffens.

I will check the wirings and inform you. I can't check it right now because I am at the work. I will inform you when I do.

I checked my mails and found out that I have already registered to Club-XM. I don't know when I did it.

By the way, thank you for your help.

[CitroJim]

As an Activa owner I feel too much roll on my Xm

As a fellow Activa owner Alper, I understand The XM should roll a little more than an Activa but not too much.

By the way, thank you for your help.

It is a pleasure Alper

Now, if you still have the Lexia, use it on a drive with a passenger watching the Hydractive live data and you will see the hydractive electrovalves switching as you drive around corners, brake, accelerate and go over large speed humps. You will be surprised at how quickly the system switches to hard, especially in sport mode.

Good to see you on Club-XM Yes, I am the same CitroJim over there

[AlperAkbilgi]

Now, if you still have the Lexia, use it on a drive with a passenger watching the Hydractive live data and you will see the hydractive electrovalves switching as you drive around corners, brake, accelerate and go over large speed humps. You will be surprised at how quickly the system switches to hard, especially in sport mode.

I have already done that. I watched my Activa switches hard mode or only opens/closes sc-car valve. But on my Xm it doesn't switch to hard mode. on the top of the lexia screen there is a box which shows the current state of suspension. it never switches to the hard mode. I can see body roll, brake position, gas pedal voltage, sport mode switch state and steering whell angle changing in the Hdractive parameter page but speed always shows 0 km.

[addo]

There's only one wire needed for continuity testing, from pin 3 of the sensor plug to pin 11 of the white Hydractive ECU plug.

[CitroJim]

OK, so the ECU very firmly believes you are not moving then If you are never moving, or so it believes, then it won't switch as the car has to be moving at greater than 30 km/h I think before it all starts working..

Do check to see if the engine ECU correctly registers speed as that will prove the sensor is good...

If I can help by providing wiring diagrams Alper then please let me know...

When the car is stopped you will see eiter 12v or 0v at the speed sensor input to the ECU and it takes only a small movement backward or forward to change this.

Does your cruise control work? I ask as the cruise ECU also uses the same sped sensor signal.

[AlperAkbilgi]

OK, so the ECU very firmly believes you are not moving then If you are never moving, or so it believes, then it won't switch as the car has to be moving at greater than 30 km/h I think before it all starts working..

Do check to see if the engine ECU correctly registers speed as that will prove the sensor is good...

If I can help by providing wiring diagrams Alper then please let me know...

When the car is stopped you will see eiter 12v or 0v at the speed sensor input to the ECU and it takes only a small movement backward or forward to change this.

Does your cruise control work? I ask as the cruise ECU also uses the same sped sensor signal.

I don't have cruise control

There's only one wire needed for continuity testing, from pin 3 of the sensor plug to pin 11 of the white Hydractive ECU plug.

How do I count it? Should I start counting form left or right?

[AlperAkbilgi]

I failed to locate the speed sensor. Where I should exactly look at?