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Home >> Chevrolet >> 2003 >> Chevy Express H2500 >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 4 (Engine Controls - Theory & Operation) >> Fuel Systems >> Fuel Control >> Open Loop Mode
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Open Loop Mode

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When engine is cold and engine speed is greater than 400 RPM, PCM operates in open loop mode. In open loop mode, PCM calculates air/fuel ratio based upon coolant temperature and MAP sensor readings. Engine remains in open loop mode until oxygen sensor reaches operating temperature, coolant temperature reaches a preset temperature and a specific period of time has elapsed after engine starts.