2002 Chevy Impala ignition switch removal

Disconnect the negative battery cable.
Disable the SIR (air bag) system.
Locate the bolts that secure the steering column jacket assembly to the instrument panel subframe. The column will tend to drop towards the seat as the bolts are loosened. Use care handling the column. In many cases, simply lowering the column allows enough room for service work.
If it is necessary to remove the column from the vehicle, at the bottom of the column, remove the pinch bolt from the intermediate steering shaft assembly universal joint. The intermediate steering shaft is the shaft that goes through the floor/cowl, connecting the steering column to the rack and pinion steering gear assembly. Carefully work the column free of the intermediate steering shaft joint and remove the column from the vehicle.

WARNING
Once the steering column is removed from the vehicle, the column is extremely susceptible to damage. Handle the column carefully.

If it was necessary to remove the column from the vehicle, secure the steering column so it won't be damaged. Never place the column directly in a vise. GM recommends their holding fixture which is basically just a piece of steel angle. One end of the angle is clamped in the vise. The column then bolts to the other angle, using the column's original mounting bracket. A similar holding tool could be shop-made.
If the column is still in the vehicle, and if necessary, the tilt lever can be removed. The tilt lever simply snaps in place. Carefully rock the lever back and forth while pulling it from the steering column
Remove the two screws from the lower shroud and remove the lower shroud. It may be helpful to tilt the shroud down and slide it back to disengage the locking tabs.
Locate and remove the two screws retaining the upper shroud. If the column is still in the vehicle, the upper shroud likely won't remove all the way since the plastic shroud surrounds the lock cylinder. Just lift the upper shroud enough to gain access to the lock cylinder release hole.
Remove the lock cylinder using the following procedure:
If the column is still in the vehicle, verify that the negative battery cable has been disconnected.
Hold the key in the START position.
Using a 1 / 16 inch Allen wrench push down on the lock cylinder retaining pin.
Release the key to the RUN position and pull the steering column lock cylinder set from the lock module assembly.

To install:

Position the upper shroud and steering column lock cylinder set observing the following:
Place the key in the lock cylinder and in the RUN position.
Make sure the sector gear in the lock module assembly is in the RUN position.
Position the lock cylinder to the upper steering column shroud.
Line up the locking tabs and positioning tab with the slots in the lock module assembly and push the cylinder into position.

Position the upper shroud and install the two retaining screws.
Install the lower shroud taking care to align the slots on the lower shroud with the tabs on the upper shroud. Tilt the lower shroud up and snap the two shrouds together. Secure with the retaining screws.
Position the shift lever seal and multifunction lever seal into position.
Install the tilt lever to the steering column by snapping into place.
Install the steering column (or raise back into place, if there was enough room to perform this procedure by simply lowering the column). Install the retaining bolts. Carefully torque to 35 ft. Lbs. (47 Nm).
If all other service procedures have been performed, enable the SIR system.

I wouldn't bother dropping the column as the cylinder as you know is in the dash. Cleaning the sensor will not do you much good. Replacement is the only fix but if you really want to try, pull the radio, hvac and you should be able to push the detent on the cylinder to release it. Make sure you take the bezel off at the cylinder first. ANd have the key in the on position.