Disconnect the battery
Locate the O2 sensor
Remove the sensor from the exhaust
Inspect the sensor tip for heavy damage or contamination
Spray the sensor tip with O2 sensor cleaner or non-chlorinated brake cleaner
Gently brush off carbon deposits with a soft brush
Soak the sensor tip in cleaner if needed
Let the sensor air dry completely
Reinstall the sensor
Reconnect the battery
Clear any stored trouble codes
Test the vehicle for proper operation