Open and Closed Loop Operation

The ECM operates in two different fuel control modes: Open Loop and Closed Loop. Whenever the vehicle is first started, the ECM operates in open loop fuel control. When the ECM determines that the pre-catalyst oxygen sensor for a specific bank is a certain amount above or below the bias voltage range, it will go into closed loop fuel control operation for that specific bank. Closed loop fuel control operation will be maintained as long as certain parameters are met.

In closed loop fuel control, the ECM varies the fuel to the engine according to signals received from the oxygen sensor located in the exhaust manifold. The oxygen sensor sends a voltage signal to the ECM indicating the oxygen content of exhaust gases. If the oxygen sensor voltage is below 450 mV signaling the air/fuel mixture is lean, the ECM will increase the amount of fuel to the engine. If the oxygen sensor voltage is above 450 mV signaling the air/fuel mixture is rich, the ECM will decrease the amount of fuel to the engine. During closed loop fuel control operation, the ECM is constantly adjusting the amount of fuel to the engine according to signals received from the oxygen sensor, in order to obtain a 14.7:1 air/fuel ratio.

If there are any oxygen sensor related diagnostic trouble codes, the ECM will not go into closed loop fuel control operation.