NOTE: Before proceeding, check for contaminates that may have damaged HO2S such as contaminated fuel, unapproved silicone, oil and coolant.

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 8 .
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.
Turn ignition off. Disconnect PCM harness connector. PCM is located in engine compartment, between air cleaner and radiator. Measure resistance of sensor ground circuit (Black/Orange wire) between 1/2 HO2S harness connector and terminal No. 27 at PCM C1 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 sensor ground circuit.
Measure resistance of signal circuit (Tan/White 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 signal circuit.
Reconnect all harness connectors. Start engine and let it idle. Measure voltage drop (backprobe connectors with voltmeter) of sensor ground circuit (Black/Orange wire) between 1/2 HO2S harness connector and terminal No. 27 at PCM C1 harness connector. If voltage drop is less than .1 volt, go to next step. If voltage drop is .1 volt or more, repair high resistance in sensor ground circuit.
With engine idling, measure voltage drop (backprobe connectors with voltmeter) of signal circuit (Tan/White wire) between 1/2 HO2S harness connector and terminal No. 51 at PCM C2 harness connector. If voltage drop is less than .1 volt, go to next step. If voltage drop is .1 volt or more, repair high resistance in signal circuit.
If no other possible causes are remaining, replace PCM.
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.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

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

Use the Manual With the Right Hardware

When to See a Mechanic

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