Open and Closed Loop Operation

The PCM operates in two different fuel control modes: Open Loop and Closed Loop. Whenever the vehicle is first started the PCM operates in Open Loop fuel control. When the PCM determines that the engine coolant temperature (ECT) sensor has reached at least 20°C (68°F), and the oxygen sensor has reached operating temperature of 318°C (600°F), it will go into Closed Loop fuel control operation. Closed Loop fuel control operation will be maintained as long as certain parameters are met.

In Closed Loop fuel control, the PCM varies the fuel to the engine according to signals received from the oxygen sensor, located in the exhaust manifold. The oxygen sensor varies a voltage signal to the PCM indicating the oxygen content of exhaust gases. If the oxygen sensor signals that the air/fuel mixture is lean, the PCM will increase the amount of fuel to the engine. If the oxygen sensor signals that the air/fuel mixture is rich, the PCM will decrease the amount of fuel to the engine. During Closed Loop fuel control operation, the PCM is constantly adjusting the amount of fuel to the engine, according to signals received from the oxygen sensor, to try and obtain a 14.7:1 air fuel ratio.

If there are any oxygen sensor related PCM/Engine Controller (EC) diagnostic trouble codes or if the oxygen sensor does not switch between rich and lean, or if the ECT does not obtain 20°C (68°F), the PCM will not go into Closed Loop fuel control operation.