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If the vehicle will not shift from Park, check the rear brake lights and see if they are working when you step on the brake pedal.
If the lights do NOT work, first check your fuses. If the fuse are ok, and still no brake lights, the problem is going to be the Brake Light Switch located at the top of the brake pedal arm. This switch controls the brake lights and also send a signal to the Shift Interlock telling it to release when the pedal is depressed.
If the brake lights ARE working, the problem is going to be in the Shift Interlock System. The shift interlock solenoid, module and cable will need to be inspected for proper operation.
In the meantime, there is an over-ride you can use to shift into Nuetral, then start the vehicle and change gears. Insert a flat tool into the over-ride hole.