VGT(Variable Geometric Turbocharger) is the device which increases the efficiency of turbocharger at low rpm and lasts optimum turbo efficiency at high rpm as varying the cross sectional area through which exhaust gas passes turbocharger impeller. It relieves turbo lag at low speed and increase engine power generation.

The electronic VGT adapted on S engine is activated by VGT actuator control unit and electronic actuator integrated with DC motor. Engine speed, APS signal, MAFS and Boost pressure sensor data are inputted to ECM. ECM controls VGT actuator control unit to control exhaust gas line as controlling VGT actuator duty to maintain optimum state of air compression. VGT actuator control unit controls DC motor with those signal so that exhaust gas can pass through the vane more or less cross sectional with operating spear gear→outter crank→ inner crank→main link→ unison ring→inner vane in order.

VGT actuator control unit judges that actuator is faulty by feed back signal of actuator position from turbo charger position sensor. If it is detected, VGT actuator control unit notifies faulty to ECM. The electronic actuator is much faster in operating response and stable in control than vacuum type.

P0238 is set when BPS output voltage is higher than maximum value (4900mV) for more than 2 sec.. This code is due to 1) short to battery / open in signal circuit or 2) open in ground circuit.

Fig.1) The waveform of BPS signal and APS signal as accelerating from idle state. Signal voltage rises as accelerating.