So my 2003 xjr is sitting 15mm lower, front and back on the left hand side.
As my car is an early one it has 4 level sensors.
Ant ideas on what is happening? Do the front and back sensors on one side work in unison or are they independent of each other?

 

If your XJR is sitting lower on the left side, it’s usually a height sensor issue. The four sensors (one at each wheel) that work separately, but the system balances the whole car based on what they read.

Check that the little sensor arms on the left front and rear are still attached and not bent. If they look fine, you’ll likely just need to recalibrate the suspension with SDD or Forscan. If one sensor gives jumpy readings, replace it.

 

Sdd ? You would find codes for a electricly worn height sensor but mechanic problem.so inspect them .
with sdd on a leveled ground and a t leat a 10 amp charger hooked to the battery you coul try to calibrate heights.
4 sensors on early models
height front 386mm mid center wheel to arch straight up is the original value
373mm on the rear .
+- 15mm up or down is fine and in tolerance
All of them but the daimler or maybe vanden plas would go down 15mm at 160km/h or 100mph after some minutes traveling.
I had right side very high stiff and undrivable, 2 right heightsensors were shot.
the fixing screws to the bracket corroded , swollen up they wrecked the plastic box then probably water ingress and frozen during the night .
changed all 4 .... comfort 10 to 15% better than before