Air/Fuel Ratio Feedback Compensation (Closed Loop Operation)

In order to obtain efficient performance of the Three-Way Catalytic Converter (TWC) and a high clarification rate of CO, HC and NOx in the exhaust gas stream, the air/fuel mixture must be kept as close to the theoretical air/fuel ratio (14.7:1) as possible. In order to accomplish this, the Powertrain Control Module (PCM) first compares the input voltage from fuel control Heated Oxygen Sensors (HO2S) with a specified reference voltage. If the fuel control HO2S input voltage is higher than the specified reference voltage, the PCM determines that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces the fuel (lean command). If the input voltage from the fuel control HO2S is lower than the specified reference voltage, the PCM determines that the air/fuel ratio is leaner and increases the fuel (rich command). By repeating these operations, the PCM can adjust the air/fuel ratio in order to be closer to the theoretical air/fuel ratio. Control of the fuel delivery system as just described is known as closed loop operation.