P0157: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

What does P0157 mean?

The oxygen signal from bank 2 sensor 2 stays below its allowed range. Exhaust leakage before that sensor can draw in oxygen and resemble lean exhaust, while a grounded signal can create a false low reading.

Generic OBD-II definition: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2). Confirm applicability in your vehicle service information.

Common causes

• Leak ahead of the downstream sensor
• Signal wire shorted to ground
• Contaminated or failed rear sensor
• An actual lean-running engine

Symptoms

• Check engine light
• Often little change in driving
• Possible poor idle if a wider mixture problem exists

Diagnostic focus

If both front and rear sensors on bank 2 read lean, investigate the bank's mixture and exhaust leaks. A lone fixed rear-sensor low signal makes its own circuit especially important.

Can I keep driving with P0157?

Severity: Low With a steady light and normal running, arrange diagnosis soon. Stop for a flashing light, severe misfire, overheating, or a glowing catalyst; do not assume those symptoms are only a sensor fault.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

• Repair verified upstream lean faults first
• Inspect exhaust joints ahead of the bank 2 rear sensor
• Test wiring and sensor response after leaks are excluded

Sources & review

• OBD-Codes.com: P0157
• TroubleCodes.net: generic code definitions

Definitions and diagnostic background checked 2026-11-06. Generic guidance, not a substitute for the service procedure for your exact year, engine, and transmission.