A diagnostic system of a vehicle for diagnosing a drive belt of a continuously variable transmission. A diagnostic circuit detects or predicts a fault of the drive belt based on an operating parameter received from a sensor associated with the vehicle during a predetermined diagnostic period.

There are provided a continuously variable transmission (CVT) in which a belt (7) is wound around a primary pulley (5) and a secondary pulley (6) to transmit power; a primary pulley rotational speed sensor (13) for detecting a rotational speed of the primary pulley (5); a vehicle stopped state determination means for determining whether a vehicle is in a stopped state; a belt slippage detection means for detecting belt slippage on the basis of a signal of the primary pulley rotational speed sensor (13); and a prohibition means for prohibiting detection of the belt slippage by the belt slippage detection means when a parking range or a neutral range is selected by a shift lever operation by a driver. In the vehicle stopped state during selection of the parking range or the neutral range, the rotational speed of the primary pulley (5) is not basically output, and the belt slippage does not occur. Thus, erroneous detection of the belt slippage can be avoided by prohibiting the detection of the belt slippage in this case.

A diagnostic system of a vehicle for diagnosing a drive belt of a continuously variable transmission. A diagnostic circuit detects or predicts a fault of the drive belt based on an operating parameter received from a sensor associated with the vehicle during a predetermined diagnostic period.