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DTC P0140: 1/2 O2 Sensor Stays At Center: Testing

NOTE: 1/2 HO2S may also be referred to as an downstream oxygen sensor. 1/2 HO2S is mounted on catalytic converter.
  1. Turn ignition on. Using scan tool, read DTCs. If Good Trip counter is displayed for DTC P0140 and displayed count is "0", go to next step. If Good Trip counter is not displayed for DTC P0140 or displayed count is not "0", go to step  8.
  2. Turn ignition off. Disconnect 1/2 HO2S connector. Connect a jumper wire between positive battery terminal and Dark Blue/Yellow wire at 1/2 HO2S harness connector. Turn ignition on. Using scan tool, read 1/2 HO2S voltage. If voltage is one volt or less, go to next step. If voltage is more than one volt, replace 1/2 HO2S.
  3. Turn ignition off. Disconnect PCM connectors. PCM is located on left side of engine compartment, near front of battery. Measure resistance of Brown/Dark Green wire between 1/2 HO2S harness connector and terminal No. 27 at PCM C1 harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Brown/Dark Green wire.
  4. Measure resistance of Dark Blue/Yellow wire between 1/2 HO2S harness connector and terminal No. 51 at PCM C2 harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Dark Blue/Yellow wire.
  5. Ensure ignition is off. Reconnect all connectors. Using voltmeter, backprobe Brown/Dark Green wire between 1/2 HO2S harness connector and terminal No. 27 at PCM C1 harness connector. Start engine and allow it to idle. If voltage is less than .1 volt, go to next step. If voltage is .1 volt or more, repair poor connection causing high resistance on 1/2 HO2S signal circuit (Brown/Dark Green wire) between 1/2 HO2S and PCM.
  6. Turn ignition off. Using voltmeter, backprobe Dark Blue/Yellow wire between 1/2 HO2S harness connector and terminal No. 51 at PCM C2 harness connector. Start engine and allow it to idle. If voltage is less than .1 volt, go to next step. If voltage is .1 volt or more, repair poor connection causing high resistance on 1/2 HO2S signal circuit (Dark Blue/Yellow wire) between 1/2 HO2S and PCM.
  7. At this time, 1/2 HO2S is assumed to be defective. Replace 1/2 HO2S.
  8. At this time, conditions for DTC to set do not exist or fault is an intermittent problem. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Using scan tool, monitor parameters related to DTC while wiggling connectors and wiring harness. If value changes while wiggling connectors and wiring harness, repair connectors and wiring harness where wiggling caused value to change. If value does not change, review Freeze Frame data using scan tool. Attempt to duplicate condition that caused DTC to set. Check for any related technical service bulletins that may apply. Visually inspect related connectors and wiring harness. Repair connectors and wiring harness as necessary. See WIRING DIAGRAMS article. If no problems are indicated, test is complete.
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