The Brake Transaxle Shift Interlock (BTSI) System is designed to keep the driver from moving the gear selector out of PARK without the brake pedal being depressed. The battery voltage is applied to the BTSI solenoid with the ignition switch in either of the following positions:

With you release the brake pedal, the solenoid energizes and the solenoid prevents the gear selector from being moved away from the PARK position.

When you depress the brake pedal, the battery voltage is no longer applied to the BTSI solenoid and the solenoid de-energizes. This allows the gear selector to move freely from the PARK position.