Circuit Description

The DTC P0505 Idle Control System diagnostic monitors the voltage on the Idle Air Control (IAC) coil circuits. The Powertrain Control Module (PCM) controls the IAC valve in order to regulate the air flow through the idle air bypass passage. The amount of air flowing through the idle air bypass passage determines the idle speed. The PCM directs the IAC valve according to changes in the engine load. The IAC valve is a stepper motor design using four coils to control the pintle position. A DTC P0505 will set if the PCM detects an unexpected voltage on any of the coil control circuits.