Circuit Description

The DTC P0125 Excessive Time To Closed Loop Fuel Control diagnostic monitors the relationship between running time and heated oxygen sensor (HO2S) activity. The HO2S produces a voltage that varies between 0.1-0.9 volt under normal operating conditions. The powertrain control module (PCM) monitors this voltage and determines if the exhaust is lean or rich. If the voltage input at the PCM is about 0.1 volt the exhaust is lean, and if the voltage input is about 0.9 volt the exhaust is rich. The PCM constantly monitors the HO2S 1 signal during Closed Loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary.

In normal operation the HO2S 1 will become active and go into Closed Loop soon after the engine is running. If the PCM fails to receive a high voltage signal from the HO2S 1 after the engine cooling system has reached operating temperatures, DTC P0125 can set.