Open Loop Mode
WARNING: This page is about a different car, the 2003 Saturn LW300 and 2003 Saturn L300. However, it is still accessible from the selected car via links, so may be relevant.
When engine is cold and engine speed is greater than 400 RPM, ECM operates in open loop mode. In open loop mode, ECM calculates air/fuel ratio based upon coolant temperature and MAP or MAF sensor readings. Engine remains in open loop mode until O2S reaches operating temperature, coolant temperature reaches a preset temperature and a specific period of time has elapsed after engine starts.