The P0509 code on your 2019 Hyundai Tucson indicates a high voltage condition in the idle air control system circuit. With electronic throttle control, this relates to throttle body or related sensor circuits showing elevated voltage.
High Voltage Analysis
High voltage in control circuits typically indicates an open condition. When a sensor or actuator circuit is broken or disconnected, the ECM sees the reference voltage without normal signal loading, resulting in a high reading.
Tucson Throttle Control
The 2019 Tucson uses electronic throttle control where the throttle body manages all engine airflow. The throttle position sensors and motor control circuits must maintain proper voltage levels for accurate idle control.
Causes of High Circuit Readings
Disconnected or damaged connector creates open circuit. Broken wiring prevents signal return. Failed sensor or actuator has high internal resistance. Corroded terminals cause poor electrical contact. An improperly installed throttle body may have connection issues.
Diagnostic Process
Use Hyundai GDS to identify the specific high-reading circuit. Check throttle body connector—ensure fully seated. Test circuit continuity from throttle body to ECM. Look for broken wires or damaged terminals. If circuits test good, the throttle body internal electronics may have failed.