DTC P0506: Idle Speed Low: Description

WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.

Idle speed is controlled by PCM via an Idle Air Control (IAC) valve. IAC valve consists of a 2-coil stepper motor that moves a pintle valve in and out from the seat controlling amount of by-pass air entering intake manifold. PCM controls IAC valve by supplying ignition voltage or ground to any of 4 circuits of coil "A" or "B". When one circuit of a coil is supplied ignition voltage, the other is supplied ground. Coil "A" and coil "B" are independent or each other, however both must be functional in order for valve to move in and out correctly. IAC position is measured in counts, which can be read on a scan tool. When engine is turned off, IAC valve is retracted as high as 145 counts allowing for maximum air during a restart. After engine is started, motor position command is based on ECT and TP sensor values. DTC sets when actual engine speed is less than desired idle speed for a certain length of time.