Run Mode

The run mode is the mode under which the engine operates most of the time. In this mode, the engine operates in either Open Loop or Closed Loop.

Open Loop
When the engine is first started and it is above 400 RPM, the system goes into the Open Loop operation. In the Open Loop, the control module ignores the signal from the HO2S, and 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. The HO2S has varying voltage output, showing that it is 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.

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

Closed Loop
The specific values for the above conditions vary with different engines. When these conditions are met, the systems goes into a Closed Loop operation. In a 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.