P0143 O2 Sensor Circuit Low Voltage Bank 1 Sensor 3

P0143 points to low voltage on the bank 1 sensor 3 oxygen sensor circuit. The downstream signal is stuck low or below expected range.

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 replace the sensor until wiring and exhaust leaks are checked at the correct bank 1 sensor 3 location.

Symptoms of P0143

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 P0143

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

Measure bank 1 sensor 3 signal voltage, ground, heater function, connector condition, and wiring continuity near the exhaust.
Inspect for short-to-ground faults, exhaust leaks, sensor contamination, damaged harness clips, and incorrect sensor connector routing.
Compare low voltage behavior with fuel trim, catalyst monitor state, deceleration fuel cut, and freeze-frame conditions.

Related OBD-II codes

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