An automotive powertrain total control system using estimated output shaft torque has been investigated in order to enhance drivability and improve fuel economy. The system provides efficient control for both the engine and transmission which leads to an enhancement in drivability by reducing shocks during gear shifts.This paper describes a new smooth gear shift control method using the total control system. By use of the estimated output shaft torque, it is possible to detect accurately the fluctuation condition and the start time of the inertia phase, which are important factors affecting shock occurrence. Torque feedback, got from estimated torque, was applied to the control of engine output shaft torque during shifts. The optimum hydraulic pressure, also got from estimated torque, was applied to the clutch of the transmission during shifts. The estimated output shaft torque of a hydraulic torque converter was calculated using the input/output shaft speed signal of the hydraulic torque converter and the hydraulic torque converter characteristics.A test vehicle utilizing an electronically controlled throttle valve was developed to verify the new smooth gear shift control method. The total control system reduced shock during 1-2 upshift by nearly 35%.