The brake transmission shift interlock (BTSI) system prevents the automatic transmission from being shifted out of the PARK position unless the following conditions are present:

When the ignition switch is in the RUN or the START position, the current flows from the B/U Lamp fuse located in the underhood bussed electrical center (UBEC) through CKT 839 (PNK) to the park/neutral position switch. The park/neutral position switch also feeds the backup lamps portion of the switch. With the transmission in the PARK position, the current flows to the BTSI fuse located in the underhood bussed electrical center (UBEC) through CKT 275 (LT GRN). The current then flows to the TCC/stoplamp switch through CKT 584 (LT GRN/BLK). The current continues to the BTSI solenoid through CKT 1135 (DK GRN/WHT). The ground path is provided through CKT 1850 (BLK) to G207. When the brake pedal is depressed, the normally closed contacts in the TCC/stoplamp switch open and the current flow is interrupted. When the current flow is interrupted, the BTSI solenoid de-energizes. The transmission may then shift to another gear. When the transmission shifts to another gear (except PARK), the contacts in the park/neutral position switch open. This condition stops the current flow to energize the solenoid when the brake pedal releases.

The brake transmission shift interlock (BTSI) system prevents the automatic transmission from being shifted out of the PARK position unless the following conditions are present:

The park lock solenoid prevents the transmission from being shifted out of the PARK position with the ignition OFF. When the ignition switch is in the RUN or the START position, the current flows from the B/U Lamp fuse located in the underhood bussed electrical center (UBEC) through CKT 839 (PNK) to the park/neutral position switch. The park/ neutral position switch also feeds the backup lamps portion of the switch. With the transmission in the PARK position, the current flows to the BTSI fuse located in the underhood bussed electrical center (UBEC) through CKT 275 (LT GRN). The BTSI fuse supplies current through CKT 584 (LT GRN/BLK) to splice pack SP204. The TCC/stop lamp switch and the park lock solenoid receive current from SP204 through CKT 584 (LT GRN/BLK). The current then flows to the BTSI solenoid via the closed contacts of the TCC/stoplamp switch through CKT 1135 (DK GRN/WHT). The park lock solenoid and the BTSI solenoid ground path is provided through CKT 1850 (BLK) to G200. When the park lock solenoid is activated, the solenoid releases the shifter so the vehicle may be moved out of the PARK position. When the BTSI solenoid is energized, the solenoid locks the shifter in the PARK position. When the brake is depressed the solenoid opens the contacts in the TCC/stop lamp switch. This action de-energizes the BTSI solenoid, which allows the shifter to be moved out of the PARK position. When the transmission shifts to another gear (except PARK), the contacts in the park/neutral position switch open. This condition stops the current flow to de-energize the solenoids.

The BTSI system also includes the park lock solenoid (located in the steering column) with floor shift transmission only. The park lock solenoid prevents the ignition key from being removed from the cylinder unless the transmission is in the PARK position. When the ignition switch is in the RUN or the START position, the current flows from the CLSTR fuse (located in the IP fuse block) through CKT 1020 (PNK) to the automatic transmission controller park switch. With the automatic transmission in the PARK position, the current flows to the park lock solenoid through CKT 1996 (YEL). The ground path is provided through CKT 1850 (BLK) to G207. The park lock solenoid energizes and unlocks the ignition cylinder. The ignition cylinder may then be turned to the LOCK position and the key may be removed. When the transmission is out of the PARK position, the park switch opens. This condition de-energizes the park lock solenoid which prevents the ignition cylinder from turning to the locked position. This prevents key removal.