Run Mode

The run mode has 2 conditions called Open Loop and Closed Loop (CL). When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The engine control module (ECM) ignores the signal from the heated oxygen sensor (HO2S). The ECM calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in Open Loop until meeting the following conditions:

• The HO2S has 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.

Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins CL operation after reaching these values. In CL, the ECM calculates the air/fuel ratio, injector ON time, based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.