Circuit Description

To provide best possible combination of driveability, fuel economy and emission control, a closed loop air/fuel metering system is used. When the vehicle is first started, PCM controls fuel delivery in open loop, ignoring H02S signals and calculates air/fuel mixture ratio based on inputs from the ECT, TPS, and MAF sensors. PCM will begin using Bank 1 HO2S No. 1 and Bank 2 HO2S No. 1 signals to control fuel delivery under closed loop conditions when following have been met:

• HO2S output signals are varying, indicating that sensors are hot enough to operate properly.
• ECT sensor indicates coolant temperature above 122°F (50°C).
• Time since start-up is at least 16 seconds for a warm engine, or 23 seconds for a cold engine.