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DTC P0131: 1/1 O2 Sensor Shorted To Ground: Testing

NOTE: 1/1 HO2S may also be referred to as an upstream oxygen sensor. 1/1 HO2S is located in outlet flange of right exhaust manifold.
  1. Start engine and let it idle. Using scan tool, read 1/1 HO2S voltage. If voltage is less than .16 volt, go to next step. If voltage is .16 volt or more, go to step  7 .
  2. With engine running, Disconnect 1/1 HO2S harness connector. Using scan tool, read 1/1 HO2S voltage. If voltage is .16 volt or less, go to next step. If voltage is more than .16 volt, replace 1/1 HO2S.
  3. Turn ignition off. Disconnect PCM harness connectors. See Figure . Measure resistance between ground and signal circuit (Black/Dark Green wire) at 1/1 HO2S harness connector. If resistance is 100 ohms or more, go to next step. If resistance is less than 100 ohms, repair short to ground in Black/Dark Green wire.
  4. Measure resistance between signal circuit (Black/Dark Green wire) and sensor ground circuit (Black/Orange wire) at 1/1 HO2S harness connector. If resistance is 100 ohms or more, go to next step. If resistance is less than 100 ohms, repair short between signal circuit and sensor ground circuit.
  5. Measure resistance between signal circuit (Black/Dark Green wire) and heater ground circuit (Black wire) at 1/1 HO2S harness connector. If resistance is 100 ohms or more, go to next step. If resistance is less than 100 ohms, repair short between signal circuit and heater ground circuit.
  6. If no other possible causes are remaining, PCM is assumed to be defective. Replace PCM.
  7. 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 wiring harness between 1/1 HO2S and PCM while monitoring 1/1 HO2S voltage 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 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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