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

Circuit is monitored for about 7 minutes after engine is warmed to normal operating temperature, with vehicle speed at 20-60 MPH, engine speed at 1150-2500 RPM, and MAP vacuum at 8.2-15.7 in. Hg. DTC will set when 1/2 HO2S voltage switches from less than .35 volt to more than .53 volt and back fewer times than required. Possible causes are: exhaust leak, high resistance in signal circuit, high resistance in sensor ground circuit, heater ground circuit open, Automatic Shutdown (ASD) relay output circuit open or defective 1/2 HO2S.