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DTC P0139: 1/2 O2 Sensor Slow Response

NOTE: Test applies only to gasoline models. For connector terminal ID, see CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS article.
NOTE: The 1/2 oxygen sensor may also be referred to as downstream oxygen sensor or secondary oxygen sensor. 1/2 oxygen sensor slow response is monitored when the engine is idling. For the first part of the test, if limits are exceeded, the test passes. If limits are not exceeded, the second part of test is performed when battery temperature sensor reading is more than 44°F (6.7°C), baro is more than 22.13" H2 O of vacuum, battery voltage is more than 10.5 volts, MAP sensor is more than 11.79" H2 O of vacuum but less than 18.15" H2 O of vacuum, engine speed is more than 1350 RPM but less than 2200 RPM and vehicle speed is more than 50 MPH but less than 65 MPH. DTC may be stored in Powertrain Control Module (PCM) if 1/2 oxygen sensor signal voltage is switching from less than .39 volt to more than .58 volt and back fewer times than required. Possible causes are: exhaust leak, defective 1/2 oxygen sensor, or defective connectors or wiring.
  1. Turn ignition on with engine off. Using scan tool, check for DTCs. If DTC SPECIFIC GOOD TRIP counter is displayed and equal to zero, go to next step. If DTC SPECIFIC GOOD TRIP counter is not displayed and equal to zero, go to step  11.
  2. Ensure ignition is on with engine off. Using scan tool, actuate oxygen sensor heater test and then use scan tool to monitor 1/2 oxygen sensor voltage for 2-3 minutes. Oxygen sensor heater test may also be referred to as O2 heater test. If 1/2 oxygen sensor voltage becomes less than 1.5 volts within 2-3 minutes, go to next step. If 1/2 oxygen sensor voltage does not become less than 1.5 volts within 2-3 minutes, go to step  6.
  3. Start engine and allow engine to idle. Check for exhaust leaks between engine and 1/2 oxygen sensor. The 1/2 oxygen sensor is located on exhaust pipe behind catalytic converter. If no exhaust leaks exist, go to next step. If exhaust leaks exist, repair exhaust system as necessary. Perform TEST VER-5 .
  4. Shut engine off. Using voltmeter, backprobe terminal No. 3 (Black/Light Blue wire) on 1/2 oxygen sensor connector and terminal A4 (Black/Light Blue wire) on PCM connector C1. This is the ground circuit for 1/2 oxygen sensor. PCM is located on firewall, near brake booster. Start engine and allow engine to idle. Warm engine to normal operating temperature and note voltage reading with engine idling. If voltage is less than .1 volt, go to next step. If voltage is .1 volt or more, repair high resistance on Black/Light Blue wire between 1/2 oxygen sensor and PCM. Perform TEST VER-5 .
  5. Shut engine off. Using voltmeter, backprobe terminal No. 4 (Tan/White wire) on 1/2 oxygen sensor connector and terminal A25 (Tan/White wire) on PCM connector C1. This is the signal circuit for 1/2 oxygen sensor. Start engine and allow engine to idle. Warm engine to normal operating temperature and note voltage reading with engine idling. If voltage is less than .1 volt, shut engine off. Replace 1/2 oxygen sensor. Perform TEST VER-5 . If voltage is .1 volt or more, repair high resistance on Tan/White wire between 1/2 oxygen sensor and PCM. Perform TEST VER-5 .
  6. Stop actuation of oxygen sensor heater test. Turn ignition off. Disconnect 1/2 oxygen sensor connector. The 1/2 oxygen sensor is located on exhaust pipe behind catalytic converter. Turn ignition on with engine off. Using scan tool, actuate oxygen sensor heater test. Using voltmeter, check voltage at terminal No. 1 (Violet/Orange wire) on 1/2 oxygen sensor connector. If voltage is more than 11 volts, go to next step. If voltage is 11 volts or less, repair open on Violet/Orange wire between 1/2 oxygen sensor and fuse No. 19/20 (15-amp). Fuse No. 19/20 receives voltage from Auto Shutdown (ASD) relay. Fuse No. 19/20 and ASD relay are located in power distribution center at driver's side of engine compartment, near battery. Perform TEST VER-5 .
  7. Stop actuation of oxygen sensor heater test. Turn ignition off. Ensure 1/2 oxygen sensor connector is still disconnected. Using ohmmeter, check resistance between ground and terminal No. 2 (Black wire) on 1/2 oxygen sensor connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open on Black wire between 1/2 oxygen sensor and ground connection. Ground connection is located at firewall end of driver's side cylinder head. Perform TEST VER-5 .
  8. Start engine and allow engine to idle. Check for exhaust leaks between engine and 1/2 oxygen sensor. If no exhaust leaks exist, go to next step. If exhaust leaks exist, repair exhaust system as necessary. Perform TEST VER-5 .
  9. Shut engine off. Reinstall 1/2 oxygen sensor connector. Using voltmeter, backprobe terminal No. 4 (Tan/White wire) on 1/2 oxygen sensor connector and terminal A25 (Tan/White wire) on PCM connector C1. This is the signal circuit for 1/2 oxygen sensor. PCM is located on firewall, near brake booster. Start engine and allow engine to idle. Warm engine to normal operating temperature and note voltage reading with engine idling. If voltage is less than .1 volt, go to next step. If voltage is .1 volt or more, repair high resistance on Tan/White wire between 1/2 oxygen sensor and PCM. Perform TEST VER-5 .
  10. Shut engine off. Using voltmeter, backprobe terminal No. 3 (Black/Light Blue wire) on 1/2 oxygen sensor connector and terminal A4 (Black/Light Blue wire) on PCM connector C1. This is the ground circuit for 1/2 oxygen sensor. Start engine and allow engine to idle. Warm engine to normal operating temperature and note voltage reading with engine idling. If voltage is less than .1 volt, replace 1/2 oxygen sensor. Perform TEST VER-5 . If voltage is .1 volt or more, repair high resistance on Black/Light Blue wire between 1/2 oxygen sensor and PCM. Perform TEST VER-5 .
  11. Start engine and allow engine to idle. Check for exhaust leaks between engine and 1/2 oxygen sensor. The 1/2 oxygen sensor is located on exhaust pipe behind catalytic converter. If no exhaust leaks exist, go to next step. If exhaust leaks exist, repair exhaust system as necessary. Perform TEST VER-5 .
  12. Turn ignition off. Inspect wiring harness and connectors between 1/2 oxygen sensor and PCM. PCM is located on firewall, near brake booster. Inspect 1/2 oxygen sensor connector and PCM connectors for corroded, pushed out, miswired or damaged terminals. Also, check for related Technical Service Bulletins (TSBs). If no problems and no related TSBs exist, test is complete. If any problems exist, repair wiring or connectors as necessary. Perform TEST VER-5 .
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