The brake transaxle shift interlock (BTSI) is comprised of the following components:

The brake transaxle shift interlock (BTSI) is a safety circuit that prevents the vehicle from accidently shifting out of PARK when the ignition is ON. The steering column is equipped with a shift interlock solenoid. This solenoid, when energized, physically blocks the gear shift lever from moving out of PARK when the ignition is ON. The shift solenoid de-energizes, allowing the gear shifter to move, by pressing the brake pedal.

When the ignition switch is turned to ON, ignition positive voltage is supplied from the ignition switch on CKT 300 (ORN) to the coil of the park relay in the rear junction block. The opposite side of the coil is wired to the rear integration module (RIM) by CKT 1615(PNK/BLK). The park/neutral position switch determines the position of the gear shifter and provides this information to the powertrain control module (PCM) via four circuits CKT 771 (BLK/WHT), CKT 772 (YEL), CKT 773 (GRY) and CKT 776 (WHT). When the gear shifter is in PARK, the PCM sends a Class 2 message informing the RIM of the position of the shifter. The RIM in turn energizes the park relay control output, which provides a ground on CKT 1615 (PNK/BLK), energizing the park relay. With the park relay energized, battery positive voltage is provided from the NSBU fuse in the rear junction block through the contacts of the park relay, CKT 275 (LT GRN), the normally-closed brake-pedal mounted stoplamp/BTSI switch connector C2, and CKT 1135 (DK GRN/WHT) to terminal A of the shift interlock solenoid. The shift interlock solenoid, which is always grounded on terminal B by CKT 350 (BLK), energizes, locking the gear shifter in the PARK position. Depressing the brake pedal opens the contacts of the stoplamp/BTSI switch connector C2, removing power from shift interlock solenoid terminal A. The solenoid de-energizes, allowing the driver to move the gear shifter out of PARK.

When the gear shifter moves out of PARK, the park/neutral position switch signals the PCM of the change via its four input circuits, and the PCM provides this information to the RIM via Class 2 message. The RIM in turn opens the park relay control, de-energizing the park relay and disabling the shift interlock solenoid. Once the vehicle is out of PARK, the shift interlock solenoid remains de-energized when the brake pedal is released and the BTSI/stoplamp switch connector C2 contacts return to the normally-closed state.