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DTC P0140: O2 Sensor 1/2 Stays At Center

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION  . For wiring diagram, see WIRING DIAGRAMS article.
NOTE: Monitored with engine running for more than 2 minutes and coolant temperature more than 170°F (77°C) in closed loop. Set condition is when upstream O2S 1/2 signal voltage is between .29-.72 volts for 30 seconds. Possible causes are: intermittent wiring harness failure, O2S 1/2 signal circuit open, O2S 1/2 ground circuit open, defective O2S 1/2 or defective PCM.
  1. Turn ignition on with engine off. Using scan tool, observe O2S 1/2 voltage for a few minutes. Wait for voltage to stabilize between .4-.6 volts. Using scan tool, actuate O2S heater test. Using scan tool, observe O2S 1/2 voltage for up to 2 minutes. If voltage is still .4-.6 volts, go to next step. If voltage is not .4-.6 volts, go to step  8 .
  2. Turn ignition off. Disconnect O2S 1/2 connector. O2S 1/2 is located downstream of catalytic converter. Inspect electrical connectors and clean/repair as necessary. Inspect O2S 1/2 connector for corroded, damaged, pushed out or miswired terminals. If connector is okay, go to next step. If connector is not okay, repair or replace connector as necessary. Perform TEST VER-5A: ROAD TEST FOR OBD II VERIFICATION  .
  3. Using a DVOM, check resistance between O2S 1/2 connector (harness side) sensor ground circuit (Black/Light Blue wire) and chassis ground. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open O2S 1/2 ground circuit.
  4. Turn ignition on. Connect a jumper wire between sensor signal circuit (Tan/White wire) and sensor ground circuit (Black/Light Blue wire) at O2S 1/2 connector (harness side). Using scan tool, observe O2S 1/2 voltage. If voltage is .2 volts or more, go to next step. If voltage is less than .2 volts, replace O2S 1/2. Perform TEST VER-5A: ROAD TEST FOR OBD II VERIFICATION  .
  5. Turn ignition off. Disconnect Powertrain Control Module (PCM) connector C2 (located nearest to rear of vehicle). PCM is located to left of Power Distribution Center (PDC) in engine compartment. Inspect electrical connector and clean/repair as necessary. Using a DVOM, check resistance of O2S 1/2 signal circuit between O2S 1/2 connector (harness side) (Tan/White wire) and PCM connector C2 terminal No. 51 (Tan/White wire). If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open O2S 1/2 signal circuit. Perform TEST VER-5A: ROAD TEST FOR OBD II VERIFICATION  .
  6. Inspect PCM C2 connector for corroded, damaged, pushed out or miswired terminals. If connector is okay, go to next step. If connector is not okay, repair or replace connector as necessary. Perform TEST VER-5A: ROAD TEST FOR OBD II VERIFICATION  .
  7. If no other potential causes are remaining, PCM is assumed to be defective. Replace PCM. Perform TEST VER-5A: ROAD TEST FOR OBD II VERIFICATION  .
  8. Turn ignition off. Disconnect O2S 1/2 connector. O2S 1/2 is located downstream of catalytic converter. Inspect electrical connectors and clean/repair as necessary. Inspect O2S 1/2 connector for corroded, damaged, pushed out or miswired terminals. If connector is okay, go to next step. If connector is not okay, repair or replace connector as necessary. Perform TEST VER-5A: ROAD TEST FOR OBD II VERIFICATION  .
  9. Disconnect Powertrain Control Module (PCM) connector C2 (located nearest to rear of vehicle). PCM is located to left of Power Distribution Center (PDC) in engine compartment. Inspect electrical connector and clean/repair as necessary. Inspect PCM C2 connector for corroded, damaged, pushed out or miswired terminals. If connector is okay, go to next step. If connector is not okay, repair or replace connector as necessary. Perform TEST VER-5A: ROAD TEST FOR OBD II VERIFICATION  .
  10. If no other potential causes are remaining, PCM is assumed to be defective. Replace PCM. Perform TEST VER-5A: ROAD TEST FOR OBD II VERIFICATION  .
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