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

NOTE: Before proceeding, check for contaminates that may have damaged HO2S such as contaminated fuel, unapproved silicone, oil and coolant.
  1. Turn ignition on. Using scan tool, read DTCs. If GOOD TRIP is displayed and equal to zero, go to next step. If GOOD TRIP is not displayed and equal to zero, go to step  6 .
  2. Turn ignition off. Disconnect 1/2 HO2S harness connector. Turn ignition on. Connect a test light between battery positive and signal circuit (Tan/White wire) at 1/2 HO2S harness connector. 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 HO2S.
  3. Turn ignition off. Wait at least 30 seconds. Measure resistance between engine ground and sensor ground circuit (Black/Orange wire) at 1/2 HO2S harness connector If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in sensor ground circuit.
  4. Disconnect PCM harness connectors. See Figure . Measure resistance of signal circuit (Tan/White wire) between 1/2 HO2S harness connector and terminal No. 51 at PCM C2 harness connector. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in signal circuit.
  5. If no other possible causes are remaining, replace PCM.
  6. Conditions that set DTC are not present at this time. Perform the following to help identify intermittent condition:
    • With engine running at normal operating temperature, wiggle related wiring harness while monitoring related parameters on scan tool. If voltage changes or DTC sets while wiggling wiring harness, repair connectors or wiring harness where wiggling caused voltage to change or DTC to set.
    • Review freeze frame information on scan tool. Duplicate conditions present when DTC was set.
    • Refer to any Technical Service Bulletins (TSBs) that may apply.
    • Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires.
    • Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals.

    If a problem is found, repair as necessary. If no problems are found, test is complete.

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