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.

DTC will set when engine is running for at least 10 minutes and not operating in closed-loop fuel control, ECT sufficient to allow closed-loop operation (68°F/20°C) but is not achieved within specified amount of time.