DTC P0508: Idle Control System Circuit Low: Description
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2001 Saturn SW2, 2001 Saturn SL2, 2001 Saturn SL1, 2001 Saturn SL, and 2001 Saturn SC2. However, it is still accessible from the selected car via links, so may be relevant.
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 low when ignition voltage should be present.