If your XM sinks fast after switching the engine off here's the most likely culprits (this list is by no means exhaustive but will do for most faults):

Logically there are three possibilities:

1)Not enough pressure produced by the pump in the first place
2)Not enough system storage (ie accumulator)
3)Significant leak but smaller than the pump capacity (hence car is able to rise because pump delivers more fluid than escapes through leak)

1) is possible but unlikely if the car reaches full height normally. If the car doesn't reach full height this may be the problem. However, there are other reasons why the car won't reach full height which has nothing to do with the pump.

2) The accumulator sphere on the pressure regulator may be low on pressure or flat. Because there is no storage capacity, the sphere pressure rises and falls very rapidly. The regulator makes a characteristic 'click-click-click-click' noise (with the engine running) as the regulator switches on and off in response to the pressure changes.

3) The suspension may fall quickly because there's a leak in the hydraulic system. If it is an external leak then there will be a puddle of LHM fluid on the ground under the car. Identifying the leak from there is usually not difficult. If no leak appears externally then it must be internal leak ie returning to the reservoir via a return pipe.

To determine if 3) and where, remove each of the return pipes from the top of the reservoir one by one with the engine stopped, doors closed and the car generally 'at rest'. If the fluid is returning to the reservoir it must be through one of the plastic/rubber return pipes. With the car still, the return pipe which has fluid coming out of it must be from the circuit with the leak.

Once the offending return pipe has been identified, use the Hydraulic diagram (Haynes or Citroen) to identify the components connected. By tracing the line from the reservoir back to the component(s) the culprit can be identified. This can be further identified by disconnecting the return pipe from the component in question to confirm the source of the fluid.

Caution: this must be carried out over a pit and with someone else in attendance. A citroen with a leak is not the kind of thing you want to get underneath.

To find out which is the correct hydraulic diagram for your car, phone Citroen, Slough and ask for 'Technical'. Having tried recently they try to put you off because you are not a dealer. Just persist and they'll eventually give in especially with some well worded emotional blackmail. They'll fax you the appropriate diagram. If not, at least ask them for the page reference number and post here. I may have the diagram from the manual and will post here if I have.

The repair required depends on the result from the investigation above which number too highly to list here. However, repair of a faulty component can sometimes be achieved by cleaning and flushing or ultimately by replacement. Other non-component faults may be solved by bleeding (in the case of airlocks) or by de-rusting and exercising (in the case of seized actuator rods/pins).

best of luck

norrie 8)