The brake transmission shift interlock (BTSI) system prevents the automatic transmission from being shifted out of PARK unless the brake pedal is depressed. When the brake pedal is depressed, the BTSI solenoid releases a lock pawl. This enables the shift linkage to move and the shift lever to operate.
When service operations are required, the BTSI system can be overridden.
For vehicles equipped with floor-mounted shift levers, an override lever is mounted on the right side of the assembly. The override lever can be accessed by removing the shift lever boot. Push the lever to the left in order to override the BTSI.
Check for the basics first. Check the BTSI fuse in the under hood fuse box.
Do the brake lights work?