DTC P0139: 1/2 O2 Sensor Slow Response: Description

Oxygen sensor monitor will run with engine idling. If 1/2 HO2S voltage has not switched from less than .33 volt to more than .61 volt and back in 411 seconds, monitor will run again only under the following conditions: ambient/battery temperature more than 44°F (7°C), barometric pressure more than 22.13 in. Hg, battery voltage more than 10.5 volts, MAP 11.79-18.15 in. Hg, engine speed 1216-1984 RPM and vehicle speed 19-46 MPH. If 1/2 HO2S voltage still has not switched from less than .33 volt to more than .61 volt and back in 411 seconds, DTC will set in PCM memory. Possible causes are: exhaust leak, high resistance in signal circuit, high resistance in sensor ground circuit or defective 1/2 HO2S.