When the shifter will not release from Park, first, check the rear brake lights and see if they are working when you step on the brake pedal.
If the brakes lights are NOT working, check the fuse in teh under-dash fuse box labeled "STOP". If the fuse is good, then the problem will be the Brake Light Switch located at the top of the brake pedal arm under the driver's side dash. This switch controls the rear brake lights and also sends a signal to the shift interlock telling it to release when the brake pedal is depressed. Inspect the electrical connector and wire harness for any loose, broken or damaged wires. Inspect the switch mount and contact points for any broken or misaligned parts. If the visual inspection checks ok, replacing the brake light switch will solve the problem.
If the brake lights ARE working and still no shifter release, then the problem will lie in the Shift Interlock system. The shift interlock module, interlock solenoid and the shifter assembly itself will need to be inspected for bro***** *****nkages or spring and tested for proper operation.
In the meantime, however... there is a shifter release over-ride button on the face of the shifter. Remove the release hole cap and stick a key inside the hole. You should now be able to move the shifter. If not, the shifter assembly is the root of the problem. If you can move the shifter, shift to Neutral and start the vehicle. You can now continue on with normal operation.
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For an image view of the over-ride location on the shifter, click here: https://www.dropbox.com/s/y0a4trhfpbcikx6/shift-rel.jpg?dl=0