Open Loop

When engine is cold and engine speed is greater than 400 RPM, ECM operates in "open loop" mode. In "open loop", ECM calculates air/fuel ratio based upon coolant temperature and Manifold Absolute Pressure (MAP) or Mass Airflow (MAF) sensor readings. Engine will remain in "open loop" operation until oxygen sensor reaches operating temperature, coolant temperature reaches preset temperature and a specific period of time has elapsed after engine start-up.