Open Loop

When the engine is first started and it is above 400 RPM, the system goes into Open Loop operation. In Open Loop, the engine control module (ECM) ignores the signal from the heated oxygen sensor (HO2S) and calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT) sensor and the manifold absolute pressure (MAP) sensor. The sensor stays in Open Loop until the following conditions are met:

• The HO2S sensor has a varying voltage output, showing that it is hot enough to operate properly.
• The ECT sensor is above a specified temperature.
• A specific amount of time has elapsed after starting the engine.