Run Mode

The run mode has 2 conditions called Open Loop and Closed Loop.

When the engine is first started and engine speed is above predetermined RPM, the system begins in Open Loop operation. In Open Loop the PCM ignores the signal from the Heated Oxygen Sensor (HO2S), and calculates the air/fuel ratio based on inputs from the ECT, MAF, MAP and TP sensors.

The system remains in Open Loop until the following conditions are met:
^ Both HO2S has a varying voltage output, showing that they are hot enough to operate properly (this depends on temperature)
^ The ECT is above a specified temperature
^ A specific amount of time has elapsed since starting the engine

The specific values for the above conditions vary with different engines, and is stored in the Electrically Erasable Programmable Read Only Memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the PCM calculates the air/fuel ratio based on the signal from various sensors, but mainly the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1 mixture.