Everytime I cut off my 2001 Impala the security light starts flashing as soon as I cut the car off and open the door.I've tried to stop it with the clicker but the flashing light will not go away unless the car is running or after so long of flashing the battery goes dead.Oh yeah,before this started I would be driving and could hear the bell that reminds u the key is in the ignition.I'm clueless,hope someone can point me in the right direction

SOURCE: 2001 impala security pass lock

I had the ignition problem in my Impala LS '01 and I solved it, my solution was to clean the 'IGN RLY' module with a little bit of WD-40 both terminals and socket, then, i put a silica gel bag near the module (in case the humidity may form tartar again) it was an instant solution, specially in rainy weather.

SOURCE: car won't start after change battery

Your vehicle has 2 ignition wires that you can put back to factory, and start the vehicle.
The wires you are looking to put back together are PINK and DARK GREEN - and found under the D/S dash. (ignition harness - right side of steering column) They will be larger in Diameter than the others.
They were cut to install the security system. They go into the "brain" and out the other side. A relay inside the BRAIN is most likely failing.
If you no longer want the alarm installed, simply match up all of the factory colors. Use crimp-on but t-connectors for secure connection.
Let me know if you need more help.

SOURCE: wont start security light stays on

Body Control Module (BCM) on both counts. Find a shop in your town that specializes in electrical systems to test it. Beware, these can be intermittent problems, so make sure they keep it until the car does what you have observed. Expect to spend about $450 for the replacment. Dealers quoted me between $700 and $1,100 for the same repair. By the way, a new BCM will probably only last you about 12 months.

SOURCE: 2001 Chevy impala had ignition switch replaced,

Turn the key to "on" and let the light flash. It should stop flashing after about ten to twenty minutes. Once the light is on steady, turn it off, then start the car. I usually put another battery on jumper cables attached to the cars battery so it does not run down and die before the system re-arms.

SOURCE: Replaced ignition switch 2003 chevy impala and car will not start

After you replace the ignition switch turn the key to start the car and release leave the key were it stops after trying to start wait 10 minutes until security light goes out turn key to full off position then repeat the above procedure two more times for a total of three on the 3rd attempt to start car wait for light to go out then turn key to full off positoion wait 10 seconds then try to start car body control module should learn new pass code and the car should start.
Big john, J@J Automotive