Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
Engine operates in open loop when first started. In open loop operation, PCM ignores oxygen sensor input and calculates air/fuel mixture based on inputs from Engine Coolant Temperature (ECT) sensor, throttle position sensor and mass airflow sensor. PCM will begin closed-loop fuel control when oxygen sensor signal is active enough and ECT sensor reaches a predetermined value. PCM expect to begin closed-loop fuel control within a specified amount of time.