C5 2006 suspension height control issues.

[gingernut]

My C5 (mark 2) rear suspension is not dropping to normal operating height

I got a tyre and brake caliper changed on the front end by a local garage. When I got home I noticed the back end was too high. I tried dropping and raising the suspension a few times but the problem persisted.
I then put the rear end on ramps for safety and checked the height correction sensor. The linkage was fine and when disconnected the sensor seemed be working as the car could be made to drop right down to lowest and right up to the highest setting. I cleaned every thing including the electrical connection. Once the linkage was reconnected the back end was still too high although the height correction seemed to be at least part working. When I sat in the boot the car would lower with my weight and then get pumped back to the starting point. It hadn't been doing that before the clean up.
My first thought was that the clamp on the anti roll bar might have moved and was thinking of undoing the clamp and adjusting it. However before I could do anything the car started raising and lowering ( rear only) on its own after I had just raised and lowered the suspension a couple of times using the control switch Inbetween the seats.
Now I am confused. I wonder if the sensor is faulty or if the problem lies elsewhere in the system. I still suspect the sensor because the problem only happens at the rear. The front operates normally.
Any help / suggestions would be very welcome.

[Gibbo2286]

Not sure if this will help.
viewtopic.php?t=64189&hilit=Height+sensor

[GiveMeABreak]

If you are sure the Height sensors are functioning correctly, you may have a faulty hydraulic block if you have H3+.

[gingernut]

After a lot of faffing about and with the assistance of a more knowledgeable Citroenhead mate we took apart the sensor and cleaned the contacts. We didn't solder them.
We also repositioned the clamp on the anti roll bar as it looked a little misaligned, possibly from when the suspension arm bearings were done recently.
It now seems to function fine.
I might order up a spare sensor but I'm not sure if it is a straight swap or if it needs to be calibrated by lexia.
AFAIK it's a standard system not the H3+.

[GiveMeABreak]

Glad that is sorted for you. They can suffer from water ingress and start to corrode, not surprising given their location. They do not need coding, but normally if replaced you may need to have the heights checked and programmed - unless you are lucky and mark exactly the location of the clamp on the axle. The height corrector sensor units are simple potentiometers - so are not multiplexed - so no programming.

[gingernut]

Thanks Givemeabreak! Glad to hear no callibrating is required. Yesterday we perfected the art of making small adjustments to the position of the clamp on the ARB and ,with a bit of trial and error, got the back end to a roughly the right height. That said I reckon getting a new sensor makes sense as it's highly likely one will play up again.

[GiveMeABreak]

Ok, just for info - The main general height adjustment is made at the factory with the clamp positioning.

After this, if the sensor is ever removed or replaced, the height sensor position with the clamp should be marked and refitted as close as possible. Then the measurement checking and adjustment procedure is used, which results in a load of measurements and calculations. From these, the ultimate values are compared with the reference values in Diagbox / Lexia and where needed if out of range, the results of the calculations are then entered into Diagbox.

The system then performs its own calculations and makes the minute adjustments to ensure the vehicle heights are within reference parameters - the fine tuning if you like.