Gear shift locked in Park position in my 1994 Jeep Grand Cherokee also unable to remove key. Replaced ignition switch and key cylinder. When started car the security system went off and shut the car down, disconnected security now gear shift is locked in park.

Does the vehicle start an run ?Can you turn the key to the off position ? And the key won't come out ? Did you try some key graphite ( lube ) ? New lock cylinder need maybe . Or is it a problem with
Steering Column Electric Park Lock
If the vehicle is equipped with a floor-mounted console gear shifter, an added safety feature is an steering column electric park lock system in the steering column. The steering column electric park lock system prevents the steering wheel from being locked when the transmission is in gear and the vehicle may be moving. The column ignition lock system consists of a steering column electric park lock and a park position switch, that is located in the A/T shift lock control switch. The steering column electric park lock contains a spring-loaded pin that mechanically prevents the ignition key cylinder from being turned to the Lock position when the transmission is not in the Park position. If vehicle power is lost or the transmission is not in the Park position, the operator will not be able to turn the ignition key to the Lock position and will not be able to remove the ignition key from the column.

Is it shifter on the floor ?
Ignition Lock Cylinder Control Actuator
If the vehicle is equipped with a floor mounted console gear shifter, it has a ignition lock cylinder control actuator system in the steering column. The ignition lock cylinder control actuator's purpose is to prevent the ignition key from being turned to the OFF position when the transmission is in gear and the vehicle may still be moving. The column ignition lock system consists of a ignition lock cylinder control actuator , and a park position switch that is located in the A/T shift lock control switch. The ignition lock cylinder control actuator contains a pin that is spring loaded out to mechanically prevent the ignition key cylinder from being turned to the lock position when vehicle transmission is not in the Park position. If vehicle power is lost, and/or the transmission is not in the Park position the operator will not be able to turn the ignition key to the lock position and will not be able to remove the ignition key from the column.

GM had problems with these ! Has a TSB - technical service bulletin !
Automatic Transmission Shift Lock Control Description and Operation
The automatic transmission shift lock control system is a safety device that prevents an inadvertent shift out of PARK when the engine is running. The driver must press the brake pedal before moving the shift lever out of the PARK position. The system consists of the following components:
• The automatic transmission shift lock solenoid (serviced as the automatic transmission shift lock actuator), as well as the body control module (BCM) and the engine control module (ECM). The shift lock solenoid is located within the floor shift control assembly with vehicles equipped with floor shift.
• The BCM controls the voltage to the shift lock control solenoid through the shift lock control solenoid controlled voltage circuit. The following conditions must be met before the BCM will remove voltage from the shift lock solenoid:
- The ignition is in the ON position.
- The engine control module (ECM) sends an input via GMLAN serial data to the BCM indicating the transmission is in the PARK position.
- The BCM determines the brake pedal is applied according the brake pedal position.
Since the shift lock control solenoid is permanently grounded, the BCM supplies voltage to the automatic transmission shift lock control solenoid, mechanically locking the shift lever in the PARK position as the solenoid energizes. When the brake pedal is applied, the BCM turns the control voltage output of the shift lock control solenoid OFF, de-energizing the shift lock control solenoid. The de-energized solenoid releases the mechanical lock allowing the driver to move the shift lever out of the PARK position. When the transmission is out of the PARK position, the shift lock control solenoid remains de-energized.
During remote start operation, the BCM will energize the shift lock control circuit, locking the shift lever in the PARK position.
Replaced shifter on a cobalt , broken plastic part inside , wouldn't press on micro switch to disengage ! Found replacement shifter at auto slavage yard .$20.00 US

replaced my ignition cylinder Anon, Check your fuses, also after changing ignition, google search if you have to do a relearn procedure.

What make vehicle ? Most all vehicles have a safety system .Don't try an force anything you'll break it !
Electronic Park Lock (EPL)/Ignition Lock Cylinder Control Actuator: If the vehicle is equipped with automatic transmission and a floor mounted console gear shift, it has an ignition lock cylinder control actuator system in the steering column. The ignition lock cylinder control actuator purpose is to prevent the ignition key from being turned to the OFF position when the transmission is in any position other than PARK and the vehicle may still be moving. The column ignition lock system consists of an ignition lock cylinder control actuator, and a park position switch that is located in the automatic transmission shift lock control switch. The ignition lock cylinder control actuator contains a pin that is spring loaded to mechanically prevent the ignition key cylinder from being turned to the lock position when the vehicle transmission is not in the PARK position. If vehicle power is lost, and/or the transmission is not in the PARK position the operator will not be able to turn the ignition key to the lock position and will not be able to remove the ignition key from the column. They also have this on column mounted shifters !

Here's something to consider..... Sometimes, when one parks against a curb, there is a tendency for the ignition switch and the gear shift to kind of get in a bind. Sometimes, forcing the steering wheel to turn a bit, one way or the other, will relieve the pressure of things so that the gear shift or the ignition switch will function properly... OR, you might try putting the gear shift in Neutral... and then returning it to Park... Just some thoughts...

Electronic Park Lock (EPL)/Ignition Lock Cylinder Control Actuator: If the vehicle is equipped with automatic transmission and a floor mounted console gear shift, it has an ignition lock cylinder control actuator system in the steering column. The ignition lock cylinder control actuator purpose is to prevent the ignition key from being turned to the OFF position when the transmission is in any position other than PARK and the vehicle may still be moving. The column ignition lock system consists of an ignition lock cylinder control actuator, and a park position switch that is located in the automatic transmission shift lock control switch. The ignition lock cylinder control actuator contains a pin that is spring loaded to mechanically prevent the ignition key cylinder from being turned to the lock position when the vehicle transmission is not in the PARK position. If vehicle power is lost, and/or the transmission is not in the PARK position the operator will not be able to turn the ignition key to the lock position and will not be able to remove the ignition key from the column.

Does your impala have floor shifter ?

Test/Service/Replace

The circuit on newer cars with automatic transmissions has a neutral safety, or neutral start switch installed between the ignition switch and the starter. The ignition switch cannot operate the starter motor unless the transmission is in park or neutral.
Late model vehicles with manual transmissions have a starter/clutch interlock switch that requires the clutch to be depressed to the floor.
Neutral Safety Switch
Normal operations of a neutral safety switch provides a quick check for the adjustment of the gear selector linkage.

• To do this, move the selector slowly until it clicks into the PARK position.
• Turn the ignition key to the START position.
• If the starter operates, the PARK position is correct.
• After checking the PARK position, move the lever slowly toward the NEUTRAL position until the lever drops at the end of the NEUTRAL stop in the selector gate.
• If the starter also operates at this point, the gearshift linkage is properly adjusted.
• This quick test also tests the adjustment of the neutral safety switch.
• If the engine does not start in either or both of these positions, the neutral safety switch or the gear selector linkage needs adjustment or repair.

CAUTION
Since you must work under the vehicle to adjust most shift linkages make sure you properly raise and support the vehicle before working under it. Also, wear safety glasses or goggles while working under the vehicle.
A voltmeter can be used to check the switch for voltage when the ignition key is turned to the START position with the shift lever in PARK or NEUTRAL. If there is no voltage, the switch should be adjusted or replaced.

Most newer models have a safety feature called
shift interlock. This prevents the key from being turned back
to the lock position if you forget to place the gear selector in park.
Depending on the model,
If it uses a cable, it may be sticking or needs adjusting.
If it uses an electrical solenoid. may be blown fuse or park switch.
Tap, shake, and pull up on the shifter and make sure it's in park.

Ignition Lock Cylinder Control Actuator
If the vehicle is equipped with a floor mounted console gear shifter, it has a ignition lock cylinder control actuator system in the steering column as an added safety feature. The ignition lock cylinder control actuators purpose is to prevent the steering wheel from being locked when the transmission is in gear and the vehicle may still be moving. The column ignition lock system consists of a ignition lock cylinder control acutator, and a park position switch that is located in the A/T shift lock control switch. The ignition lock cylinder control acutator contains a pin that is spring loaded out to mechanically prevent the ignition key cylinder from being turned to the lock position when vehicle transmission is not in the Park position. If vehicle power is lost, and/or the transmission is not in the Park position the operator will not be able to turn the ignition key to the lock position and will not be able to remove the ignition key from the column.

take a small hammer and tap the lock cylinder where the key goes in then retry. if this does work you should have the lock cylinder replaced soon as it has internal problems