Citroen XM Forum

Hi all,

Short intro: My name is Jan, I live in the Netherlands.

I owned a ´99 turbo diesel before, it was the best and most comfortable car I ever had.
Then bought a C5 X7 tourer, but I never really liked it.
Now with the diesel prices and the fact that I am working from home, I bought a ´92 2.0i comfort in Blanc Meije.

Currently I am learning about Hydractive I and reading fault codes from ECU's.
I always maintained my cars myself (except for the C5), so I know a bit about wrenching and hope to share that here.

Hydractive 1 is normally very reliable and is simple to diagnose.
If you don't have one build a blink code reader and start a thread on the forum, as we can help you more there.

A Hydractive 1 system can't normally switch to hard at one end without switching at the other also, as they are hydraulically connected, not electrically, as Hydractive 2.
Hard at the front is probably the centre sphere, but don't forget the corner spheres are smaller and stiffer on Hyd 1 than Hyd 2, the centre sphere is larger, but overall volume across the axle is less, at 1,300cc, as opposed to 1,350cc.
In essence: Hyd 2 systems are softer and more compliant than Hyd 1 systems, which are tuned for a slightly more sporty ride.

Wire a tell-tale LED/low wattage bulb into the electrovalve feed to see when the system is in hard/soft mode.

Is there two versions of h1, or is the front and rear electric centre blocks, from around 1994 H2?

Wasnt there two ecu versions for H1? Or is this getting complex. Does h1 suffer diode issues or is that just systems from 1994 onwards?

There are three versions of Hydractive1 Ecu
H1 is the very original Ecu with external timer relay and white and green connectors, which was updated in early 1990
H2 version with internal timer relay and black and white connectors. This is for 1990-1991 Xm with multiple earth type looms.
H3 version is for Hydractive 1 fitted to Xm with ring earth type looms. 1991-1993.

Hydractive 2 was introduced in February 1993 and used H4 Ecu, very late sytems using H5 Ecu.

Hydractive 1 systems don't suffer with diode failure that Hydractive 2 systems do, as the diodes are built into the Ecu, whereas on Hydractive 2 systems the diodes are inside the elctro-valves and suffer heat damage.

Being a '92 car, this will have bolt down Gnd connectors and an H3 Ecu.

I would need to look up the Rp numbers for all the change points of Ecu versions, but the above date references should be accurate enough.

I have a h5 ecu in the shed came across it Monday.. by very late systems do you mean late cars ..

citroenxm wrote: ↑

Thu Nov 17, 2022 8:27 am

I have a h5 ecu in the shed came across it Monday.. by very late systems do you mean late cars ..

Yes.
I believe H5 fitted both Xm and Xantia and is soft programmed for the specific model on demand, whereas previous versions were hard programmed for the specific model they were made for.

I’ve fitted a H5 ECU to my PRV that had a H3 originally and it works perfectly.

I'm surprised at that, as H3 Ecu is for Hydractive 1 system and H5 Ecu is for H2 system, which have different wiring configurations.

What year is your V6 that you fitted the H5 Ecu to?

Dieselman wrote: ↑

Sun Nov 27, 2022 11:24 am

What year is your V6 that you fitted the H5 Ecu to?

Ha I note the year is missing from his prv xm on the end of his signature..