Abstract: A hydraulic control system for a 4 drive speed automatic transmission, comprising:(a) a hydraulic control system for a 3 drive speed automatic transmission, including two shift valves and two solenoid valves associated with said two shift valves, respectively; and(b) an additional shift valve actuated in response to a hydraulic relay signal or signals generated by said two shift valves.Further, to reduce an unpleasant shock generated when the transmission is kicked down from the 4th to the 2nd speed range, a passage is provided for connecting between a port of the 3-4 shift valve and a port of the 1-2 shift valve, to drain fluid supplied to the B.sub.1 brake via the 1-2 shift valve in communication with an oil supply passage connected to the C.sub.3 clutch via the 3-4 shift valve.

Abstract: An automatic transmission control apparatus detects an abrupt loss of signal from the speed sensor due to failure of the speed sensor and shifts the automatic transmission to a higher gear ratio. The control apparatus detects the engine rotation and the position of the shift lever so that when the engine rotation is under a predetermined level the control apparatus allows the automatic transmission to be shifted by the position of the shift lever.