Closed Loop Operation

When the ECM has determined conditions suitable for entering closed loop operation (based on many sensor values), it uses the oxygen sensor signal to determine the exact concentration of oxygen in the exhaust stream. From this signal, the ECM determines whether the mixture is richer (low 02) or leaner (high 02) than the ideal 14.7 to I air/fuel ratio:

• If the oxygen sensor signal is above 0.45 volt, the ECM determines that the air/fuel mixture is richer than ideal and decreases the injection duration.

• If the oxygen sensor signal is below 0.45 volt, the ECM determines that the air/fuel mixture is leaner than ideal and increases the injection duration.

During normal closed loop operation, the oxygen sensor signal switches rapidly between these two conditions, at a rate of more than 8 cycles in 10 seconds at 2500 rpm. Small injection corrections take place each time the signal switches above and below the 0.45 threshold voltage.

Closed loop control works on the premise of the command changing the condition and can be summarized as follows:

• 02S indicates rich = ECM commands leaner injection duration

• 02S indicates lean = ECM commands richer injection duration

In short, the oxygen sensor informs the ECM of needed adjustments to injector duration based on exhaust conditions. After adjustments are made, the oxygen sensor monitors the correction accuracy and informs the ECM of additional adjustments. This monitor/command cycle occurs continuously during closed loop operation in an effort to keep the air/fuel mixture modulated around the ideal ratio.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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