When I drive the car, come to the parking area, switch to the parking/any gear and try to switch off the car, the key does not turn completely to "off" state. It get stuck to ACC. But when I remove the "Body Function Control Module/Instrument Panel Cluster" fuse from "Instrument Panel Fuse Block - Driver's side", then the key turn to "off" state and then all lights are off(when the key is in ACC, speedometer light continuously glow on).

Again when I start the car and switch off the car, it goes to "off" state but when I change the gear or drive the car, again the key stuck to ACC. Every time I have to do this activity(removing fuse and switching off the car and then reinserting the fuse) for the battery to not get drained.

FYI... my mechanic has already replaced the key ignition switch.

Request all of your help in fixing this problem.

"FYI...my mechanic has already replaced the key ignition switch."

How about the key interlock solenoid?

State make and model. This will help us help you.

It's a Chevrolet malibu 2002 model...

Kitch is on the right track. Shops are reporting numerous problems with the wiring to the park interlock switch in the gear shifter. Have your tech check for a broken wire.