Run Mode

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

Open Loop
When the engine is first started and engine speed is above 637 RPM, the system goes into Open Loop operation. Also, when the engine is first started and the throttle position has not changed, the system remains in Open Loop, until the throttle is moved. When the system is in Open Loop operation, the PCM ignores the signal from the O2S and calculates the air/fuel ratio based on inputs from the Engine Coolant Temperature (ECT) and Manifold Absolute Pressure (MAP) sensors. The system stays in Open Loop until the following conditions are met:
- The O2S has varying voltage output, showing that it is hot enough to operate properly. This depends on temperature.
- The ECT sensor is above a specified temperature.

Closed Loop
Specific values for the above conditions exist for each different engine, and are stored in the Electronically Erasable Programmable Read Only Memory (EEPROM). When these values are met, the system goes into Closed Loop operation. The PCM calculates the air/fuel ratio (injector on-time) based on the signal from the O2S.This allows the air/fuel ratio to stay very close to 14.6:1.