P0142

Code

Generic P — Powertrain

O2 Sensor Circuit Bank 1 Sensor 3

Brand: Generic

Type: P — Powertrain

Views: UK: 20 EN: 33 RU: 25

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Scan for related codes and freeze frame data (confirm Bank 1 / Sensor 3 location)
Visual inspection of sensor and harness for damage, corrosion, soot, or exhaust leaks
Verify connector is fully seated and pins are clean and undamaged
Check for signs of contamination on the sensor tip (soot, oil, coolant)
Inspect nearby exhaust components and flange gaskets for leaks
Check vehicle service information for sensor location and expected pinout

Typical narrow‑band O2 sensor signal (upstream) ~0.1–0.9 V (switching rapidly); downstream sensors usually more stable near ~0.4–0.6 V — values vary by vehicle
P0142 often triggered when sensor signal is persistently very low (near 0.0–0.2 V) or circuit voltage is below expected threshold
Heater circuit resistance (if equipped) commonly in the low ohm range — consult OEM spec for exact resistance
Backprobe voltages: key on engine off — reference power ~5 V (if applicable) and heater supply ~12 V (if equipped) — check vehicle manual for correct values

Retrieve all DTCs and freeze frame, note conditions when code set; attempt to reproduce if safe
Visually inspect sensor, connector and wiring for damage, corrosion, melted insulation or contamination; repair as needed
Verify correct sensor identification (Bank 1 Sensor 3) using vehicle service data
With connector connected, backprobe the signal wire and observe live data with a scan tool during key ON and engine running; note voltage behavior
If circuit shows low voltage, check for short to ground: with ignition off measure continuity between signal wire and ground; no continuity expected
Check for short to 12V: measure continuity between signal wire and battery positive; none expected
Verify heater supply and ground (if sensor has heater): with key ON measure voltage at heater power pin and check heater resistance to ground against OEM spec
Wiggle wiring harness while monitoring signal to detect intermittent shorts/open circuits
Check for exhaust leaks upstream of the sensor and repair if present
If wiring and power/grounds are good and connector pins check out, replace the sensor with a known good or OEM-equivalent unit
After repair or replacement, clear codes and perform a drive cycle or readiness test to confirm the fault does not return
If problems persist, consider ECM/PCM testing or replacement only after all wiring and sensors are verified good