Hi all, reading through the cit hydractive training manual, i came across an interesting point.This states that the ECU'S installed in both xm and xantia are the same unit.It seems that the control laws for both models are embedded, and that the unit is designated it's model usage on the prodution line by serial link sending the correct activation code.This opens up another avenue for experimenting with ride/road holding and spare procurement.All the repair manual references categorically state that you should not use the incorrect application of ECU.Is this just cit speak or will the cars become unstable i wonder?I also noted that the ECU for the DK5 engine has modified control laws and again should not be used in the wrong application.I find all this very curious.Does anyone have further info?

As long as mine works - I don't care

Peter.N.

When PR.net was still free I spent some time looking at this. From what I remember there was no commonality of part numbers for Hydractive ECU's between Xant & XM.

Apart from the superb Activa , I would guess that as long as the ECU is from the same family (H1, H2, H3, H4, etc) the differences between ECU's for xantia and XM would be subtle if not unnoticeable,

Are the plugs & wiring the same?

Hi Robert

I too have been looking at suspension ECU's and have come to somewhat similar conclusions about them. The earlier Mk2 XM ECU's were hard coded on manufacture hence the different part numbers. The later ones are coded for a particular car on an ELIT and the dealer is required to mark the case of the ECU with the car type. The coding tables are not available from Citroen. I have not got as far as finding the devices inside these ECU's that store the tables to work out whether they are electronically reprogrammable. Still busy trying to sus out this information for the 2.5 TD engine ECU as I get time. In this ECU an EPROM is used so I doubt the XM suspension ECU is any further advanced electronically.
On the question of suspension parameter changes this is an area to enter only from a position of knowlege not for experimenting and putting other road users at risk. Previously I have led work outside the car field with analysing the inputs that cause suspension instability. We had a case of 3 major accidents in less than 24 hours after a fitter started lubricating the friction dampers on some vehicles. It was not the primary part of the suspension but the dampers became cyclic amplifiers increasing the bounce until the vehicles became unstable and left the track.

Regards

XMexc

My S1 24v has got a H4 or is it a 3, I cant remember off hand now, ECU on it, I know its not a H1 or 2 anyway. Dont know if all other hydraulic related items were swapped over from the donar car, but it DOES make the suspension work, switching between hard and soft with door opening, and with switch change on centre console..

Ask GordonJCP when he shows up again, he, and David Hallworth, saw it last year when I was in Glasgow...

Theres no ECU faults on it..

Rgds

C

Hi citroenxm, I appreciate your thoughts, with regard to the DK5 engine hyd ECU, i'm curious to know if the control laws differ from those embedded in other engine variants, and why? The basic vehicle weight and it's distribution throughout the model range does not vary greatly-that is hatch to hatch and estate to estate-nor wheel or tyre sizes, whereas the xantia does differ in all respects and i would expect the control laws to be modified accordingly(but not to the level of instability,the sphere pressures and volume are the primary suspension factors).I've only driven a 2.5 once and then only 10 miles or so ,it was that drive that convinced me the difference between the 2.1 was not as great as i thought it would be,(power application,smoothness) and the added complexity of home maintenance ruled it out.Never driven a V6 either come to that.However i digress.Many thanks for your reply and i look forward to any more thoughts you or anyone else that contribute to this site may have.