Circuit Description

The DTC P0125 Engine Coolant Temperature (ECT) Excessive Time to Closed Loop Fuel Control diagnostic monitors the time passed before closed loop fuel control occurs. The engine operates in open loop when first started. In open loop, the Powertrain Control Module (PCM) ignores the oxygen sensor signal and calculates the air/fuel ratio based on inputs from the engine coolant temperature sensor, the throttle position sensor, and the mass air flow sensor. The PCM will begin closed loop fuel control when the oxygen sensor signal is active enough and the ECT sensor reaches a predetermined coolant temperature. The PCM expects to begin closed loop fuel control within a specified amount of time.