Code 25 (PRIZM) - Oxygen Sensor, Lean Exhaust Indicated: Notes

Oxygen (O2) sensor produces a varying voltage as engine reaches normal operating temperature. Voltage will vary from .1 (lean) to 1.0 (rich) volt. ECM monitors voltage and determines concentration of gases in exhaust and adjusts fuel to maintain air/fuel ratio. Code 25 will set if sensor input voltage at ECM is less than .45 volt for 90 seconds or more with sensor warm and engine speed greater than 1500 RPM, vehicle speed is less than 60 MPH, and engine coolant temperature is greater than 122°F (50°C). Code 25 will also set if engine speed varies more than 15 RPM over preceding crank angle period for 30 seconds while idling with engine coolant temperature greater than 122°F (50°C).

1. Checks for faulty sensor.
2. Checks for open in Black wire between ECM and sensor.
3. Checks for open in Brown wire between ECM and G106.
4. Checks for short to ground in Black wire between ECM and sensor, open in Brown wire to sensor (federal emissions only), and a faulty ECM.