Code
P0142
GWM
P — Powertrain
- O2 sensor circuit fault (bank 1, sensor 3)
Views:
UK: 10
EN: 13
RU: 8
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal wiring or heater circuit
- Corroded, loose or damaged sensor connector
- Failed O2 sensor (internal fault or contamination)
- Exhaust leak upstream of the sensor
- Contaminated sensor from oil, coolant, silicone or fuel additives
- Failed PCM/ECM or poor ground at control module
Symptoms
- Check Engine/Malfunction Indicator Lamp (MIL) illuminated
- Failed emissions or readiness test
- Possible reduced fuel economy
- Possible roughness or loss of catalytic efficiency (usually minimal drivability change if sensor is downstream)
What to check
- Retrieve freeze-frame and pending data with a scan tool; confirm DTC and occurrence conditions
- Visually inspect sensor, wiring harness and connector for heat damage, corrosion, chafing or disconnection
- Backprobe the sensor signal with a scan tool or multimeter to observe voltage behaviour while engine is running
- Measure heater element resistance (with sensor disconnected) per vehicle specification
- Check for exhaust leaks upstream of the sensor
- Wiggle test wiring while observing live data to identify intermittent faults
Signal parameters
- Narrowband sensor signal voltage: ~0.1 V (lean) to ~0.9 V (rich); a properly functioning downstream sensor may show slower, low-amplitude changes compared to upstream
- Heater element resistance (typical heated O2 sensor): usually low ohms (commonly 2–40 Ω) — check vehicle spec
- Sensor should respond to rich/lean changes; long term inactivity or fixed voltage indicates a fault
- No continuity or short to battery/ground on heater or signal circuits is a fault condition
Diagnostic algorithm
- Verify code and conditions: read DTC, freeze-frame and live data. Clear code and road-test to confirm reappearance.
- Visual inspection: examine sensor body, connector and harness for heat, corrosion, breaks or soot/oil contamination.
- Connector check: disconnect connector and inspect pins/pins for corrosion or loose terminals; clean or repair as needed.
- Signal test: backprobe signal wire with engine running; observe voltage. Downstream sensors are typically steadier but should not be completely inactive (flatline).
- Heater test: with ignition off, measure heater circuit resistance between heater terminals. Compare to OEM spec. Check for open/heavy resistance or short to ground.
- Power/ground checks: verify sensor heater power supply and ground at the connector with a DVOM; check fuses and relay if applicable.
- Wiggle/pressure test: with live data visible, wiggle harness and apply light pressure to exhaust joint to detect intermittent faults or leaks.
- Repair wiring or connector faults found. Replace sensor if tests indicate internal failure or contamination.
- After repair, clear codes and verify repair by running the vehicle to ensure the code does not return and readiness monitors complete.
Likely causes
- Broken or chafed wiring between sensor and ECM
- Bad sensor connector (corrosion or bent pins)
- Sensor element failed from age or contamination
- Heater circuit open/short (if sensor is heated)
- Exhaust leak causing incorrect sensing downstream
Fault status
Status
P0142 - O2 sensor circuit fault (Bank 1, Sensor 3). Check sensor, wiring/connectors, heater circuit and ECM inputs.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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