P0157 O2 Sensor Circuit Low Voltage Bank 2 Sensor 2

P0157 indicates low voltage on the bank 2 sensor 2 oxygen-sensor circuit. The downstream 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 replace the catalyst because of this code alone; a downstream sensor circuit fault can mimic catalyst-monitor problems.

Symptoms of P0157

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 P0157

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 downstream sensor signal wiring, connector condition, exhaust leaks, and sensor ground path.
Compare bank 2 sensor 2 voltage with upstream sensor behavior, fuel trims, and catalyst-monitor readiness.
Inspect for a signal short-to-ground, damaged harness, or mixture condition that can keep the downstream signal low.

Related OBD-II codes

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