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DTC P0140: 1/2 O2 Sensor Stays At Center

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 when engine is running for more than 2 minutes and engine coolant temperature is more than 170°F (76.7°C). DTC may be stored in Powertrain Control Module (PCM) if downstream oxygen sensor signal voltage is .35-.55 volt for 1.5 minutes. Possible causes are: defective downstream oxygen sensor, defective PCM, or defective connectors or wiring.
  1. Start engine and warm engine to normal operating temperature. With scan tool in ACTUATOR TESTS mode, set engine speed at 1500 RPM. With scan tool in SENSOR mode, read downstream oxygen sensor state. If downstream oxygen sensor state switches, go to next step. If downstream oxygen sensor state does not switch, go to step  4 .
  2. With engine at 1500 RPM, wiggle wiring harness and connectors at downstream oxygen sensor while monitoring downstream oxygen sensor state on scan tool. 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, if downstream oxygen sensor state does not become locked at center while wiggling wiring harness and connectors, go to next step. If downstream oxygen sensor state becomes locked at center while wiggling wiring harness and connector, repair open on wiring harness or connectors between downstream oxygen sensor and PCM as necessary. PCM is located between driver's side front fender and power distribution center, near battery. Perform TEST VER-5A  .
  3. Turn ignition off. Check for defective wiring or connections at downstream oxygen sensor and PCM. PCM is located between driver's side front fender and power distribution center, near battery. If no defective wiring or connections exist, test is complete. If defective wiring or connections exist, repair as necessary. Perform TEST VER-5A  .
  4. Turn ignition off. Disconnect downstream oxygen sensor connector. 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, using ohmmeter, check resistance between engine ground and terminal No. 3 (Black/Light Blue wire) on wiring harness side of downstream oxygen sensor connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open ground circuit on Black/Light Blue wire between downstream oxygen sensor and PCM. PCM is located between driver's side front fender and power distribution center, near battery. Perform TEST VER-5A  .
    NOTE: On 2.4L, 3.0L late build, 3.3L and 3.8L, Black/Light Blue wire on wiring harness side of downstream oxygen sensor connector comes from downstream oxygen sensor as Black/Light Blue wire and changes to Black/Orange wire at connectors B33 and E36, and goes to terminal No. 27 (Black/Orange wire) on Black PCM connector C1. Connectors B33 and E36 are located near front of driver's side of frame rail. See Figure .
  5. Connect jumper wire between terminal No. 4 (Tan/White wire) on wiring harness side of downstream oxygen sensor connector and positive battery terminal. Turn ignition on with engine off. Using scan tool, read downstream oxygen sensor voltage. If downstream oxygen sensor voltage is one volt or less, go to next step. If downstream oxygen sensor voltage is more than one volt, replace downstream oxygen sensor. Perform TEST VER-5A  .
  6. Turn ignition off. Disconnect jumper wire from wiring harness side of downstream oxygen sensor connector and positive battery terminal. Disconnect PCM connectors. PCM is located between driver's side front fender and power distribution center, near battery.
  7. Using ohmmeter, check resistance 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. If resistance is less than 5 ohms, replace PCM. Perform TEST VER-5A  . If resistance is 5 ohms or more, repair open on Tan/White wire between PCM and downstream oxygen sensor connector. Perform TEST VER-5A  .
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