A control for a hydrokinetic torque converter lockup clutch having a clutch plate that cooperates with a torque converter impeller shell to define a control pressure cavity wherein the clutch plate is subjected to the pressure in the torus circuit of the torque converter and wherein an electronically controlled valve system is used to modulate the pressure in the control pressure cavity thereby varying the clutch capacity to establish a controlled degree of slip of the clutch so that the actual slip of the clutch may be maintained at a target slip value which is adjusted depending upon the value of input shaft speed data and throttle position data stored in the memory of a microprocessor, the microprocessor being designed to calibrate a desired slip value for each engine torque and turbine speed condition whereby a closed-loop electronic control may be achieved to provide a partial converter bypass during the major portion of the vehicle operating time.