Citroen XM Forum

Diodes are one way electrical valves, which allow electrons to flow in one direction, but not the reverse direction.

Place them in the wiring loom near the suspension Ecu.
One end of each diode connects to the +ve feed wire to each electrovalve, the other end is connected to the Gnd wire.

Download Gabor's circuit diagrams for Series 2, Xm, which shows the diode mod.
Your car has Hydractive 2, so the wiring is the same, possibly with wire colour and fuse number differences.

If really necessary, we might be able to supply diagrams for S1, but might not have them for Xm with H2 system.

Gabor's circuit diagrams.

download/file.php?id=9711

This is how to fit the diodes - important to get them the right way round!!** The sheet also gives details for adding tell-tale LEDs, so you can monitor when the suspension switches between Firm and Soft.
You can ignore that part, and just fit the two Protection Diodes, if you want to keep the job simple.

** For this job, the diodes are 'reverse connected', to protect the suspension ECU from the voltage 'spike' when the electrovalves switch off; they also to allow the EVs to hold-in properly. In this case, the band/stripe on the diode goes to +, other end to Gnd. (A diode spec of 400v is recommended, as the switch-off spike can be many times the voltage they're normally fed with.)

I wasn't aware we had that "How To" reference.
It's very useful and well put together.

Thanks for creating that, white_exec.

Ditto. I didn't know either..

It NEEDS moving to the suspension section and made sticky too...

Good idea. It's been posted many times over the years, in response to susp.mode issues.

It is in the Self Help Files, I had forgotten about it, having never needed it.

viewtopic.php?f=13&t=9749

I've stuck it to the top of hydraulics now too.. Prehaps the wrong area..

That seems fairly easy to do without the leds anyway. Another question boys. I did have a leak from the front accumulator, not the sphere but right at the bottom of the unit. Seems lhm shouldn’t be down that far, I sort of sealed it though but the pressure has driven it through again. It really needs a new unit but the one in my donor car is surely different. I could have another go at a seal or get another unit if anyone knows of one? but I also have a leak to the right of the accumulator, another contraption which is dripping green, that’s to the right if you re facing forward, more to the drivers side. I need to look at that too. Does anyone know what it is and where the leak is likely to be on it? High pressure union? Is there a return there? Direction appreciated.

Have never had a leak problem from the Accumulator/Pressure Regulator on the 2.5, but have had dripping from the same unit on the BX. There, it was both the return (it returns to the reservoir) and a couple of the main pressure unions not being tight. Tightening lessened the leaks, but did not stop them completely; fitting new union seals (small sleeves) cured it.

Worth buying a set of single-hex flare nut spanners (eg from Amazon) for any work on hydraulic unions or bleed screws, as this avoids damaging the screws. Smallest you'll need is 8mm. (Flare nut spanners are like ring spanners, but have a cut-out to enable them to be slipped over the pipe.)

To pinpoint the leak, clean and dry the area, and run up to find the source.
Also check/renew the Acc sphere seal.

On the regulator there are three metal pipe unions, the rubber/plastic return pipe, which could be leaking, fixed by tightening, or new seals.
On the side of the body is a plastic cap, which holds the cut out spring and the base cap with the cut in spring.
The spring caps are sealed with O rings, but if it I the base, ensure the base mounting bolt is tight before going further.
A loose bolt allows the base to move up and down, which causes it to leak.

The unit next to the regulator is the Flow Distribution Valve (FDV).
The end caps are sealed with O rings.

If you don't feel confident in stripping and resealing these units, Pleaides will do it for you.
Neither unit is hard to strip down.