Run Mode

The run mode has 2 conditions referred to as open loop and closed loop. When the engine is first started and the engine speed is above a predetermined rounds per minute, the system begins open loop operation. The ECM ignores the signal from the heated oxygen sensor (HO2S). The engine ECM calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), the manifold absolute pressure (MAP), and accelerator pedal position (APP) sensor. The system stays in open loop until meeting the following conditions:

• The heated oxygen sensor (HO2S) has varying voltage output, showing that the heated oxygen sensor (HO2S) 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 programmable read-only memory (EEPROM), which may be erased electrically. The system begins closed loop operation after reaching these values. In closed loop, the ECM calculates the air/fuel ratio, injector ON time, based upon the signal from various sensors, but mainly from the heated oxygen sensor (HO2S). This allows the air/fuel ratio to stay very close to 14.7:1.