DTC P0509: Idle Control System Circuit High: Description

The Idle Air Control (IAC) valve consists of a 2-coil stepper motor controlling a pintle. PCM pulses a signal to the IAC valve by switching the high and low side circuits, depending on which direction the pintle needs to move. The amount of movement being commanded is displayed in counts on scan tool. With engine off, IAC pintle is retracted (80-100 counts) allowing maximum air during a restart. After start-up, the motor position commanded is based on coolant temperature and TP sensor values. PCM monitors IAC circuit for low and high voltage faults. DTC will set when either coil "A" or "B" is commanded on or off and voltage on one side of coil circuit is high when it should be grounded.