Circuit Description

O2S1 produces a voltage that varies between 0.1-0.9 volt under normal operating conditions. PCM monitors this voltage and determines if exhaust is lean or rich. If voltage input at PCM is about 0.1 volt, exhaust is lean. If voltage input at PCM is about 0.9 volt, exhaust is rich. PCM constantly monitors O2S1 signal during closed loop operation and compensates for a lean or rich condition by adjusting injector pulse width as necessary. DTC P0125 will set when engine is at normal operating temperature, and O2S1 output does not indicate RICH within 7.5 minutes when following conditions are met:

• Engine speed at 1500 RPM or more.
• Vehicle speed at 25-62 MPH.
• Throttle valve position is open.
• Engine has been running for at least 140 seconds.