Abstract: A control system is provided for controlling a turbocharger in a turbocharged engine in response to engine power setting when the engine is operated at a power level above a selected minimum or relatively low power level and in response to altitude when the engine is operated at the low power level. A primary controller controls the position of a waste gate valve to control turbocharger compressor discharge pressure in response to engine throttle setting when the engine is operated above the low power level, and a pair of secondary controllers control the position of the valve in response to altitude when the engine is operated at the low power level to control the compressor discharge pressure in a selected manner up to a predetermined altitude and to vary the discharge pressure as a selected function of altitude above the predetermined altitude.