P0142 O2 Sensor Circuit Malfunction Bank 1 Sensor 3

P0142 indicates an oxygen sensor circuit malfunction on bank 1 sensor 3. The downstream sensor signal or circuit is not behaving normally.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not diagnose catalyst efficiency from this circuit code until the bank 1 sensor 3 circuit is repaired.

Symptoms of P0142

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0142

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Check bank 1 sensor 3 signal voltage, heater operation, ground, connector condition, wiring continuity, and exhaust-side harness damage.
Compare sensor activity with catalyst monitor operation, fuel changes, deceleration fuel cut, and nearby downstream sensor data.
Verify the vehicle actually uses bank 1 sensor 3 and confirm sensor position before replacing or testing parts.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.