The following is really just some comments to the comments raised by DKAnders.
Motor fuse value, normally fuses are fitted to protect the wires that feed a device not to protect the device itself, however in this case the burn point of the wires and motor are probably very close
There was thread on this subject in another forum where a contributer claimed that:-
a: fuse failure was a very common problem on earlier Mk1's and that
b; Citroen garages routinely replaced the 50A fuse with a 60A and that the Mk2 actually had an 80A fuse, although I believe it may be a different pump motor on the Mk2 so probably doesn't count. I don't know if what was quoted was really as widespread as stated but IMHO increasing the fuse to 60A FOR THE PURPOSES OF TEST at least initially should be o.k will give few more seconds of run time which may usefull when troubleshooting.
For the motor to take enough current it must be doing work this implies either a very high pressure and low flow or hi flow and lower pressure. Now my instinct is that the pump could probably supply it's "short circuit" (hydraulic) max flow without exceeding it's max current rating, the hydraulic circuit load would be low resulting in increasing motor speed, motor current will fall for increasing speed.
The converse is true for supply into a dead end, the pump motor will operate close to stall with a corresponding increase in current draw.
So in this case my gut feel is that the motor runs for as long as it takes to raise the rear suspension after which both outlets are shut and it is driving into a dead end, the only hydraulic flow is any leakage around the electrovalves and pump elements.
For this to happen it has to be that one or both the height sensors are telling the controller that the suspension is not at the correct height, that the front or back or both are too low.
Of course it could be that the pump unit really does have a problem access to a Lexia would make troubleshooting this so much easier
However for the moment assuming that the pump unit is good then the evidence is that the front height sensor is either shot or not set up correctly and is providing information to the pump that the suspension is too high, or there is a leak in front cylinder producing a total pump pressure high enough to get the tail up but not high enough to lift the heavier front. This seems the most likely scenario as if it was the height sensor then the moment the rear got to level the pump should shut off, it seeing the front as already being too high.
On this analysis I would suggest that Anders suggestion of checking return leak rate should be done on the front struts.