First, loosen the rear wheel lug nuts for 1999 Deville models, block the front wheels and then lift the back of the vehicle, securing it tightly on jackstands placed under the unibody frame. Remove coil spring, toe link and knuckle to lower control arm nut and bolt to disconnect control arm from knuckle. Reinstall in reverse order of removal making sure that all suspension fasteners are torqued accordingly. Raise outer end of lower control arm with a floor jack before tightening knuckle-to-control arm bolts, control arm inner pivot bolts and toe link bolts to simulate normal ride height. Turn ignition key to On position; Electronic Level Control system needs about 45 seconds to pressurize before lowering vehicle and tightening lug nuts according to torque specs.For removal of upper control arm on 1999 Deville models, remove the wheel after loosening rear wheel lug nuts then block front wheels raising back part of vehicle ensuring it is safe on jackstands placed beneath unibody frame members (not under suspension support). Disconnect ELC height sensor link and road sensing suspension position sensor bracket by removing wheel first. Then, take off knuckle-to-upper control arm nut & bolt as well as upper control arm nut & bolt which will enable you remove control arms from vehicle completely. Tighten all suspension fasteners using torque specifications; reassemble in reverse order of removal process including this step.Remembering also that before lowering car turn ignition key on while Electronic Level Control System pressurizes itself for about 45 seconds.It remains only to tighten lug nuts according to torque specs.For 2000 and later models DTS/Deville as well as all Seville vehicles you should begin by loosening rear wheel lug nuts blocking front wheels raising back part of vehicle safely onto jacks stands located right below it's a body subframe members (not under supports). Remove brake rotors calipers exhaust systems springs electrical connectors from wheel speed sensors. Disconnect all wiring harnesses and airlines from the suspension support including the ELC link(s) from the control arm(s). If necessary, remove hub and bearing assembly then take off toe link and stabilizer bar link from suspension arm being removed. Put floor jack under front and rear sections of suspension support, remove bolts from front section of suspension support as well as remove two bolts from rear part of suspension support lowering jacks slowly. Finally, undo control arm pivot bolts and detach control arm from suspension support.For installation follow reverse order of removal but make sure that all suspension fasteners are tightened to proper torque. Raise end of lower control arm with a floor jack before tightening control arm pivot bolts to simulate normal ride height. The torque specifications must be followed when tightening brake caliper bolts. Before lowering vehicle turn ignition key on while Electronic Level Control System pressurizes itself for about 45 seconds.In conclusion tighten lug nuts by means of torque wrench indicator according to specs.