Circuit Description

To provide the best possible combination of driveability, fuel economy, and emission control, a "closed loop" air/fuel metering system is used. When vehicle is first started, Engine Control Module (ECM) controls fuel delivery in "open loop", ignoring Heated Oxygen Sensor (HO2S) signals and calculating air/fuel ratio based on inputs from Engine Coolant Temperature ECT, Throttle Position (TP), and Mass Air Flow (MAF) sensors. ECM will begin using Bank-1 HO2S-1 and Bank-2 HO2S-1 signals for controlling fuel delivery under "closed loop" conditions when the following conditions have been met:

• HO2S-1 and HO2S-2 output signals are varying, indicating that H2OSs are hot enough to operate properly.
• ECT sensor indicates coolant temperature above 50°C (122°F).
• Time since start-up is at least 16 seconds for a warm engine or 23 seconds for a cold engine.