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 brake lights are NOT working- the problem will lie in the brake light switch, located under the driver's side dash, at the top of the brake pedal arm (if pressing the brake pedal hard solved the problem once before, this is more than likely the root of the problem). 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 (again, if pressing the pedal hard before worked, make absolutely sure there are no misaligned parts). If the visual inspection checks ok, replace the brake light switch.
If the brake lights ARE working and still no shifter release, then the problem will lie in the shift interlock system. Common fail item here is the shift interlock solenoid. It's located at the base of the shifter assembly. Inspect the shifter assembly mechanical items for any broken spring or links and check for any misaligned parts. If the visual inspection of the shifter checks ok, suspect a faulty solenoid.
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