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When the shifter will not shift from Park, first- Check your rear brake lights to see if they are working when you step on the brake pedal.
If the brake lights are NOT working, check your fuses. If the fuses are good, and still no brake lights, then the problem will be the Stop Lamp Switch located at the top of the brake pedal arm. 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. Carefully inspect the electrical connector for any loose, broken or damaged wires. If the visual inspection checks ok, replacing the switch will solve the problem.
If the brake lights ARE working, then the problem is going to be in the Shift Interlock system. Most commonly, the Interlock Solenoid. The interlock solenois is located on the steering column, behind the steering wheel and clockspring assembly. Again, inspect the electrical connector for any damaged or loose wires. If the visual inspection checks ok, suspect a faulty Interlock SOlenoid.