P0151 O2 Sensor Circuit Low Voltage Bank 2 Sensor 1

P0151 indicates low voltage on the bank 2 sensor 1 oxygen-sensor circuit. The upstream bank 2 signal is lower than expected.

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 assume low voltage proves a bad bank 2 sensor; a real lean condition or wiring problem can set the same code.

Symptoms of P0151

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 P0151

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 for exhaust leaks, lean bank 2 fuel trims, low fuel pressure, unmetered air, and oxygen-sensor signal wiring faults.
Compare bank 2 sensor 1 response with commanded enrichment and with bank 1 upstream sensor behavior.
Inspect connector pins, sensor ground, harness routing, and contamination that can bias the signal low.

Related OBD-II codes

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