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 the Heated Oxygen Sensor 1 (HO2S 1) with a specified reference voltage. If the HO2S 1 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 HO2S 1 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.

Closed Loop Fuel Control Operation:

The closed loop fuel control operation will not take place under any of the following conditions:
^ At engine start up.
^ When the fuel injection is increased just after engine start up.
^ When the Engine Coolant Temperature (ECT) sensor is indicating a low coolant temperature.
^ When the engine is operating under a high demand, such as Wide Open Throttle (WOT).
^ At fuel cutoff.
^ When the HO2S 1 is cold, open loop operation.