my back suspension in a citroen c5 is not raising up when the car is started

sinclair C5 dont have suspension.

l had this on my Citroen-It was due to a stuck valve under the middle of the car not allowing fluid to the rear suspension.

Sounds like the hydro-pneumatic suspension (hydraulic) has failed.

It could be electronic (relatively simple), or it could be mechanical (total part replacement).

I'd take it to a Citroen dealer first and get a diagnosis. Then find out the part number, then try and find the part cheaper on the Internet or from a breakers yard.

Failing that, there is always Ebay.
(Link enclosed).

The suspension should not have sunk in the first place! It could be the potentiometer attached to the rear anti roll bar. This sets the height on a C5. You could have a faulty connection on the BH l (Built in Hydractive Interface), this basically is the electronic pump that controls the suspension, it is behind the driver is headlamp in the engine bay. It has the LDS (suspension/steering fluid) reservoir on top of it. The LDS level may be too low. There could be a wiring fault somewhere. There r many possibilities for this, l would take it to a dealer, they will do a diagnostic check on it & advise u best.

Change the pneumatic valve