citroen xantia rear wont come up?

i am trying to check my lhm fluid level,i have started the car up set the ride hight to high,the front flys up no bother but the rear does nothing,so cant check the levels had a look under the car every thing seems to be attached and the rod that runs from the lever works fine,any ideas
when i first start the car the rear does go up to normal ride height,just wont go to full
citroen xantia 1.8 16v estate cheers phill