Here are the most likely culprits:
* Shift Interlock Cable/Solenoid: This is the most common cause. The cable or solenoid that releases the park pawl (the mechanism holding the transmission in park) might be worn, broken, sticking, or electrically faulty. It could be failing to receive the correct signal to unlock, especially when the engine is running and additional electrical load is present.
* Brake Pedal Switch: If the brake pedal switch isn't properly signaling that the brake is depressed, the shift interlock system won't allow you to shift. A worn switch, loose connection, or even debris preventing proper contact can cause this.
* Transmission Range Sensor (TRS): This sensor informs the car's computer about the current gear position. A faulty TRS can lead to communication errors that prevent the release from park.
* Low Voltage/Electrical Problems: In some instances, low battery voltage or a faulty connection in the car's electrical system, especially if it is more pronounced when the engine is running and the electrical load is higher, could prevent the proper functioning of the shift interlock components.
* Steering Column Lock: While less likely to be directly related to the *park* issue itself, a problem with the steering column lock could indirectly prevent shifting, as the system might detect a problem.
What to do:
1. Check the brake lights: Do your brake lights work? If not, the brake light switch is a prime suspect.
2. Inspect the shift interlock cable (if accessible): Look for any obvious damage, fraying, or binding in the cable. This might require some disassembly depending on the car's design. *Warning:* Don't force anything.
3. Have it professionally diagnosed: This is the most reliable method. A mechanic can properly test the shift interlock system, the brake pedal switch, and the TRS using a scan tool to identify the specific malfunction. They can also rule out other potential causes.
Ignoring the problem could lead to difficulties shifting gears, even if you can currently get it into gear when the engine is off. Repairing the shift interlock issue is crucial for safe operation of your vehicle.
