The powertrain control module (PCM) adjusts the boost pressure by controlling the turbocharger wastegate control actuator of the turbocharger. Boost pressure becomes higher by fully closing the turbocharger wastegate control valve driven by the turbocharger wastegate control actuator. The turbocharger wastegate control valve position is detected by the turbocharger wastegate control actuator position sensor and the signal is input to the PCM for target position feedback control. The turbocharger wastegate control actuator position sensor value when the turbocharger wastegate control valve is fully closed is stored as fully closed learning value. Target and actual positions are represented by the relative value from the fully closed position. The PCM sets a target position, and outputs a drive signal to the driver IC and drives the turbocharger wastegate control actuator to be equal to the target position. If the turbocharger wastegate control actuator position sensor output voltage is out of normal range for a specified time, the PCM detects a malfunction and stores a DTC.