Circuit Description

A closed loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy and emission control. When engine is first started, the PCM controls fuel delivery in open loop, ignoring HO2S signal and calculating air/fuel ratio based on inputs from engine coolant temperature, TP sensor position and mass airflow sensors. PCM will begin using HO2S signal for controlling fuel delivery (closed loop) when HO2S signal is varying, ECT is greater than 50°F (10°C), and at least 50 seconds from cold engine start-up.

DTC will set when an excessive amount of time passes before ECT reaches the closed loop threshold. The amount of time ranges between 2-13 minutes depending on coolant temperature at start-up and amount of air cycled through the engine since start-up.