The shift control system controls each gear position using a map stored in the powertrain control module (PCM) memory. The shift control system controls the CVT drive pulley pressure control solenoid valve and the CVT driven pulley pressure control solenoid valve based on vehicle speed and the throttle position to keep the drive pulley speed close to the target rpm. It does this by varying the hydraulic pressure applied to the drive and driven pulley and providing feedback on the difference between the target drive pulley speed and the actual drive pulley speed when driving. It supplies high hydraulic pressure to the driven pulley and enlarges the driven pulley belt diameter when shifting to a lower ratio. It supplies high hydraulic pressure to the drive pulley and enlarges the drive pulley belt diameter when shifting to a higher ratio. If the difference between the target drive pulley speed and the actual drive pulley speed falls within a certain range when in D, S, L, or R, the PCM detects a malfunction in the CVT shift function and stores a DTC.