DTC P0506: Idle Control System - Low Rpm: Description
WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2003 Hummer H2, 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, and 2003 GMC Cab & Chassis Sierra. However, it is still accessible from the selected car via links, so may be relevant.
The Throttle Actuator Control (TAC) system uses various inputs from the Powertrain Control Module (PCM). This system uses the inputs in order to control the idle speed through serial data circuits to the TAC module. The DC motor, which is located in the throttle body, activates the throttle plate. In order to decrease idle speed, the TAC module commands the throttle closed reducing air flow into the engine and the idle speed decreases. In order to increase the idle speed, the TAC module commands the throttle plate open allowing more air flow. If the actual idle RPM does not match the desired idle RPM within a calibrated time, this DTC sets.