C5 2006 2.0 HDI Exclusive - rear suspension sinking when parked

[estateFan]

Hi,
came out one morning recently and found the rear of the car had sunk while parked.
Pressed the key fob to unlock the car and the pump kicked in, rising the car to normal height.

I raised the car using the usual suspension button, disconnected the car battery and put axle stands under the car before giving each piston/ram rubber gaiter a squeeze to
see if any fluid had accumulated from a possible seal failure. All looked good. Took the stands away and reconnected the battery.

If a single piston or both pistons were compressing, then the fluid must be getting past the pump valve. A reasonable assumption.
Everything I read here and speaking to the local Citroen parts dept. suggested these pumps hardly ever fail ( although the electric motors can fail particularly due to corrosion ).

So next step was to take the car computer out of the equation to check if the pump valve was mechanically good.
When I got to work I disconnected the car battery . 9 hours later the car had not sunk. So reconnected the car battery to drive home.

The suspension did not sink all day and has been working fine ever since.

It looks like disconnecting the car battery for 20 minutes did not help but 9 hours did. It may turn out that the rear height sender unit is having intermittent problems
and the car battery fix was just a coincidence but I have come to the conclusion over the last few years that the car management software leaves a bit to be desired and
can't be trusted. In any event, disconnecting the battery every six months or so is probably worth doing with these cars.

Hope this information is helpful to someone.

Thanks.

[GiveMeABreak]

Could be a sticking rear height corrector or the linkage - raising and lowering a few times may have resolved it - but I would get some grease on it. Nothing really to do with the software - the BSI doesn't control the suspension and the suspension ECU uses the data from the height correctors. There is the possibility of the return LDS return valve sticking in the rear hydraulic block though.