Air Suspension Will Not Level Out - 6'' different side to side.

Rear air suspension will not level out correctly on the left hand side - if you manipulate the right hand level sensor up or down the suspension reacts straight away, you can hear the valve's click in and out and either the relief valve open and suspension lower or compressor cut in and suspension raises. This does not happen on the left hand side. The voltages on the 3x wires to the left sensor are the same as to the right hand sensor and the left hand level sensor has been repalced. The suspension does raise and lower on both sides if you use the extended rear clearance switch in the dash - but when returning to normal level the vehicle always sits between 2 and 6 inch's different wheel arch height side to side. Thanks