What Is the Function of the Brake Transmission Shift Interlock (BTSI) System and Neutral Safety Switch and How Do You Diagnose or Replace It on Lexus RX350?

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The Brake Transmission Shift Interlock (BTSI) system consists of two solenoid-operated devices, one located near the ignition key lock cylinder and the other on the shift lever assembly beneath the center console. The solenoid on the shift lever assembly includes a Shift Lock Module that receives signals from the brake pedal switch and the transaxle range sensor to activate the key lock solenoid and the shift lock module. In 2015 and later models, the shift lock solenoid and module are replaced by a steering lock ECU and actuator mounted on the steering column. The shift lock module secures the shift lever in the PARK position when the ignition key is in the LOCK position, and the only way to unlock the shift lever is by pressing the brake pedal when the ignition key is in the RUN position. The system also prevents the ignition key from being turned to LOCK unless the shift lever is in PARK. To verify proper operation, ensure the ignition key can only be removed in PARK, that it can rotate from OFF to LOCK only when in PARK, and that the shift lever cannot be moved out of PARK with the ignition key in OFF, RUN, START, ACC, or LOCK positions without pressing the brake pedal. Once in gear with the ignition key in RUN, the shift lever can be moved between gears without pressing the brake pedal. If the BTSI system malfunctions, adjustments may be necessary. For replacement, disconnect the cable from the negative battery terminal, remove the steering column trim covers, access and disconnect the ignition key lock solenoid, and remove its mounting screws. For Highlander models and 1999-2003 RX 300 models, remove the shift lever assembly, console bulb connector, and shift lock module mounting screws to separate the module from the assembly, with installation being the reverse of removal. For 2004 and later RX 330 models, similar steps apply, including removing the position indicator slide cover and lower housing. The transmission range sensor provides Park/Neutral function and prevents engine start in any gear other than Park or Neutral; adjustments may be needed if the engine starts in the wrong position. In case of BTSI failure, an override feature allows manual operation with the parking brake ON and the engine OFF by locating and pressing the override button next to the shift lever, with specific instructions for accessing the button on 2015 and later models.

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