Run Mode

The run mode has two conditions called Open Loop and Closed Loop.

When the engine is first started and the engine speed is above a predetermined RPM, the system goes into Open Loop operation. In Open Loop, the control module ignores the signal from the HO2S. The control module calculates the air to fuel ratio based on the inputs from the Engine Coolant Temperature (ECT) sensor and Manifold Absolute Pressure (MAP) sensor. The system stays in Open Loop until the following conditions are met:
1. Both HO2S have varying voltage output, showing that they are hot enough to operate properly. This depends on engine temperature.
2. The Engine Coolant Temperature (ECT) sensor is above a specified temperature.
3. A specific amount of time has elapsed after starting the engine.

The specific values for the above conditions vary with different engines. When these conditions are met, the system enters Closed Loop operation. In Closed Loop, the control module calculates the air to fuel ratio (injector on-time) based on the signal from the HO2S. This allows the air to fuel ratio to stay very close to 14.7:1.

A normal functioning system may go into Open Loop at idle if the Heated Oxygen Sensor (HO2S) temperature drops below the minimum requirement to produce the voltage fluctuation.