Patent ID: 7935016

Claim:
An automatic transmission comprising: a planetary gear mechanism; an engagement element group including a plurality of friction engagement elements to achieve a plurality of gear positions in the planetary gear mechanism, at least one of the friction engagement elements being a particular engagement element including first and second pressure chambers to which a hydraulic fluid pressure is to be supplied to actuate the friction engagement element; a pressure control valve to regulate the hydraulic fluid pressure to be supplied to the particular engagement element; a selector valve arranged to connect the second pressure chamber of the particular engagement element with the pressure control valve when the selector valve is at a first valve position, and to disconnect the second pressure chamber from the pressure control valve when the selector valve is at a second valve position; and a shift control section configured, to command a shift operation from a first gear position in which the particular engagement element is disengaged, to a second gear position in which the particular engagement element is engaged, by controlling the selector valve to the second valve position to disconnect the second pressure chamber from the pressure control valve and by supplying the hydraulic fluid pressure from the pressure control valve to the first pressure chamber of the particular engagement element, and to judge the selector valve to be in an abnormal state in which the selector valve is unable to disconnect the second pressure chamber from the pressure control valve, in accordance with a parameter in the shift operation from the first gear position to the second gear position.