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

Monitor will run with engine idling. If 1/2 HO2S voltage switches from less than .39 volt to more than .58 volt and back fewer times than required within 60 seconds, monitor will run again only under the following conditions: ambient temperature more than 44°F (7°C), barometric pressure more than 22.13 in. Hg, battery voltage more than 10.5 volts, MAP sensor vacuum 11.79-18.15 in. Hg, engine speed 1350-2200 RPM and vehicle speed 50-65 MPH. If 1/2 HO2S voltage still switches from less than .39 volt to more than .58 volt and back fewer times than required, 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.