Hi All

Currently on a mini holiday in Scotland (Glasgow area), but travelled up in my V6 24v machine, pictures else where..

But, I have noticed after a bit of comparison, that the Hyroactive SPORT mode still worked. The car a 1991 S1 24v - normally the ECU's have stopped working.. Anyway, upon investigating I have found that the car has a H3 computer fitted and it works fantasitcly!! Of course this is a good thing, and makes the car handle VERY well.

My point to all this is, should the H3 be on this car?? Would the previous owner, also an XM fanatic, needed to have changed all Hydroactive items from the 1993 K reg 24v in which the engine came from??

It makes the car ride brilliantly, and for a S! car, has NO electrical vices what so ever. All ABS, brake failure warnings, bulb warnings are non existant! Which makes driving this machine an absolut JOY!!

The only thing to need repair is the Air Con condenser which I have and will replace sometime soon..

Are there many other XMs in a PERFECT electrical state?? I wonder...


HAPPY XM'ing....

Regards
citroenxm

Hi citroenxm

Your car was after the initial ones where the suspension anti-jolt relays were external to the ECU. The use of the H3 ecu is perfectly valid; the only difference is that most of the switching parameters were eased which made for a better ride ie hard switching on a roundabout came in later and went soft earlier so you were not on the straight and accelerating whilst hard mode was still switched in. I had done this on my 1991 V6 12v, and had a small lamp to indicate when it was switching the centre speheres in or out - there was a marked difference from the H2 box to the H3..

JohnM

PS - nothing else needs to be changed at all

Hi,

I might be totally off the mark, but if the 1993 car you refer to had the later suspension with two separately controlled electrovalves, then this would be driven by an H4 ecu would it not?

I believe that the 1993 model had both electrovalves switched from a single source, it didn't change until later in the production run

Hydractive 1: ecus were labelled H1, H2 and H3 (h1 had external jolt relays H2 and H3 were very similar but with the softer parameters I mentioned)
Hydractive 2 started with the H4 ecu


I think.........

JohnM

Hi All

Just to add a little more information on H4 suspension ECUs. I think it was during the 1996 model year that Citroen changed the version of the H4 to a programmable (once only) universal one. They all have the same part number marked on the case but are then programmed in car with the suspension charecteristics to suit the particular XM model or Xantia. So secondhand H4 units may be a bit of a lottery unless someone has marked on them the original model type.

Regards

XMexc

I have circuit diagrams for all (probably) the variations. I'll try to do som detective work this weekend. It would be very nice if I could use my spare H4 unit in my 24V. It's way to quick to harden... hmmm out of context that could be quite funny

I thought the programmable ecu had only two possible settings, Xantia or XM?

Derek

Hi Derek

I came across the programmable H4 when it was stated that the 2.5TD has its own set of suspension tables. It tended to suggest that they used the programmability to give each model its own finely tuned table of suspension values. I must start jotting down a note each time I come across an interesting reference then I could easily check back.

Regards

XMexc

Thank you XMexc.

Regards, Derek

I have an H5 ECU on my desk waiting to be opened.
I've been told that it is useless without the associated immobiliser code that you put in the keypad. Is this correct?
Thanks
Steve

Hi Archman1

I do not know about H5 ECU's but H3 & H4 ECU's are suspension ECU's and have nothing relating to the XM immobiliser in them.
It is the Main XM (engine) ECU that stores the Immobiliser code and if it is set then you need the code to start the car with that ECU. These main ECU's need to be the correct type for the particular model and age of XM. There is a chance that your ECU has been set to the Garage code (see Owners Manual). There are specialists that will read/reset codes in ECU's but at considerable cost.

Regards

XMexc