Circuit Description

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

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

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