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DTC P0139: 1/2 O2S Slow Response

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION  . For wiring diagram, see WIRING DIAGRAMS article.
NOTE: The 1/2 O2 sensor is referred to as downstream oxygen sensor in this test. Downstream oxygen sensor operation is monitored with engine running, engine at normal operating temperature and ambient air temperature is more than 20°F (-7°C). DTC may be stored in Powertrain Control Module (PCM) if downstream oxygen sensor signal voltage does not become more than .53 volt and less than .35 volt once during vehicle drive cycle. Possible causes are: engine mechanical problem, fuel contamination, exhaust leak, slow responding downstream oxygen sensor, defective oxygen sensor heater, or defective connectors or wiring.
  1. Using scan tool, check for DTCs. If GLOBAL GOOD TRIP counter is not displayed and equal to zero, go to next step. If GLOBAL GOOD TRIP counter is displayed and equal to zero, go to step  8 .
  2. Note location of downstream oxygen sensor. On 2.4L, downstream oxygen sensor is mounted near rear of catalytic converter. On 3.0L, 3.3L and 3.8L, downstream oxygen sensor is mounted on exhaust pipe, behind catalytic converter.
  3. On all models, turn ignition on with engine off. On 2.4L, 3.0L late build, 3.3L and 3.8L, using voltmeter, check voltage on downstream oxygen sensor ground circuit by backprobing between terminal No. 3 (Black/Light Blue wire) on wiring harness side of downstream oxygen sensor connector and terminal No. 27 (Black/Orange wire) on Black PCM connector C1. This wire comes from downstream oxygen sensor as Black/Light Blue wire and changes to Black/Orange wire at connectors B33 and E36. Connectors B33 and E36 are located near front of driver's side of frame rail. See Fig 1 . On 3.0L early build, using voltmeter, check voltage on downstream oxygen sensor ground circuit by backprobing between terminal No. 3 (Black/Light Blue wire) on wiring harness side of downstream oxygen sensor connector and terminal No. 43 (Black/Light Blue wire) on Gray PCM connector C2. On all models, PCM is located between driver's side front fender and power distribution center, near battery.
    Fig 1: Locating Connectors B33 & E36
    G00005719Courtesy of DAIMLERCHRYSLER CORPORATION
  4. On all models, check voltage drop while wiggling wiring harness and connectors between PCM and downstream oxygen sensor. If voltage drop is less than .1 volt while wiggling wiring harness and connectors, go to next step. If voltage drop is .1 volt or more while wiggling wiring harness and connectors, repair poor connection causing high resistance on downstream oxygen sensor ground circuit between downstream oxygen sensor and PCM. Perform TEST VER-5A3  .
  5. Ensure ignition is on with engine off. Using voltmeter, check voltage on downstream oxygen sensor signal circuit by backprobing between terminal No. 4 (Tan/White wire) on wiring harness side of downstream oxygen sensor connector and terminal No. 51 (Tan/White wire) on Gray PCM connector C2.
  6. Check voltage drop while wiggling wiring harness and connectors between PCM and downstream oxygen sensor. If voltage drop is less than .1 volt while wiggling wiring harness and connectors, go to next step. If voltage drop is .1 volt or more while wiggling wiring harness and connectors, repair poor connection causing high resistance on downstream oxygen sensor signal circuit (Tan/White wire) between downstream oxygen sensor and PCM. Perform TEST VER-5A3  .
  7. At this time, conditions for downstream oxygen sensor slow response does not exist or is an intermittent problem. Using scan tool, read FREEZE FRAME data while attempting to duplicate the condition that caused DTC to be set by paying special attention to the conditions that downstream oxygen sensor is monitored. Downstream oxygen sensor operation is monitored with engine running, engine at normal operating temperature and ambient air temperature is more than 20°F (-7°C). If downstream oxygen sensor slow response reoccurs, go to next step. If downstream oxygen sensor slow response does not reoccur, condition no longer exists. Perform TEST VER-5A3  .
  8. Start engine. Check exhaust for excessive smoke caused by coolant entering combustion chambers or high oil consumption. If excessive smoke caused by coolant entering combustion chambers or high oil consumption does not exist, go to next step. If excessive smoke caused by coolant entering combustion chambers or high oil consumption exists, repair engine as necessary and replace downstream oxygen sensor. Perform TEST VER-5A3  .
  9. Check for exhaust leaks between engine and catalytic converter. If no exhaust leaks exist, go to next step. If exhaust leaks exist, repair exhaust system as necessary. Perform TEST VER-5A3  .
  10. Turn ignition on with engine off. Using voltmeter, check voltage on downstream oxygen sensor signal circuit by backprobing between terminal No. 4 (Tan/White wire) on wiring harness side of downstream oxygen sensor connector and terminal No. 51 (Tan/White wire) on Gray PCM connector C2. On 2.4L, downstream oxygen sensor is mounted near rear of catalytic converter. On 3.0L, 3.3L and 3.8L, downstream oxygen sensor is mounted on exhaust pipe, behind catalytic converter. On all models, PCM is located between driver's side front fender and power distribution center, near battery. If voltage drop is less than .1 volt, go to next step. If voltage drop is .1 volt or more, repair poor connection causing high resistance on downstream oxygen sensor signal circuit (Tan/White wire) between downstream oxygen sensor and PCM. Perform TEST VER-5A3  .
  11. Turn ignition on with engine off. On 2.4L, 3.0L late build, 3.3L and 3.8L, using voltmeter, check voltage on downstream oxygen sensor ground circuit by backprobing between terminal No. 3 (Black/Light Blue wire) on wiring harness side of downstream oxygen sensor connector and terminal No. 27 (Black/Orange wire) on Black PCM connector C1. This wire comes from downstream oxygen sensor as Black/Light Blue wire and changes to Black/Orange wire at connectors B33 and E36. Connectors B33 and E36 are located near front of driver's side of frame rail. See Fig 1 . On 3.0L early build, using voltmeter, check voltage on downstream oxygen sensor ground circuit by backprobing between terminal No. 3 (Black/Light Blue wire) on wiring harness side of downstream oxygen sensor connector and terminal No. 43 (Black/Light Blue wire) on Gray PCM connector C2. On all models, PCM is located between driver's side front fender and power distribution center, near battery.
  12. On all models, if voltage drop is less than .1 volt, replace downstream oxygen sensor. Perform TEST VER-5A3  . If voltage drop is .1 volt or more, repair poor connection causing high resistance on downstream oxygen sensor ground circuit between downstream oxygen sensor and PCM. Perform TEST VER-5A3  .
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