O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
The P0157 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2). This is a low severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $80 - $300 (O2 sensor $60-$200; labor $50-$150)
Test O2 sensor voltage (should fluctuate 0.1-0.9V). Do not replace a $150 sensor without confirming it is actually bad first.
Shows real-time O2 sensor readings on your phone. See if the sensor is lazy, stuck, or actually working before spending money.
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Common Symptoms
- Check Engine Light on
- No significant drivability symptoms
- Slightly increased emissions
- Catalyst monitor may not complete
- Possible emissions test failure
Probable Causes (Ranked by Likelihood)
- Failed downstream O2 sensor (bank 2) stuck reading low Very High
- Exhaust leak after the catalytic converter on bank 2 High
- Wiring short to ground in the signal circuit Moderate
- Corroded sensor connector Moderate
- Failing catalytic converter on bank 2 Low
Frequently Asked Questions
Can I drive with code P0157?
Yes, you can drive normally. The downstream sensor on bank 2 monitors catalytic converter efficiency only. Its failure does not affect fuel control or engine performance.
Could P0157 indicate a bad catalytic converter?
Possibly. If the catalytic converter on bank 2 has failed, it can produce exhaust conditions that cause a low sensor reading. However, a failed sensor is much more common. Replace the sensor first and see if the code returns.
Is P0157 the bank 2 version of P0137?
Yes. P0137 is O2 sensor low voltage for bank 1 sensor 2, and P0157 is the same fault on bank 2 sensor 2.
What actually makes the computer set an oxygen sensor code?
The OBD II regulation requires four separate detections for an oxygen sensor (Title 13 CCR 1968.2, section (e)(7.2)): deterioration in voltage, response rate or amplitude that would push emissions past 1.5 times the FTP standards; loss of circuit continuity; out-of-range values; and the case where the sensor has degraded enough that the fuel system stops using it and falls back to open loop. A sensor can therefore set a code while still producing a signal that looks plausible on a scan tool. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Monitor bank 2 sensor 2 voltage on a scan tool. The downstream sensor should show relatively stable voltage (0.5-0.7V). A fixed low reading (below 0.2V) suggests a lean condition or failed sensor.
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Check for exhaust leaks between the catalytic converter and the downstream sensor on bank 2.
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Disconnect the sensor and check signal wire for a short to ground (should be infinite resistance to ground).
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Inspect the connector for corrosion, water intrusion, or damaged pins.
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If the sensor is good, evaluate the catalytic converter on bank 2 for efficiency.
Sources 3
This page is built from documented references. Verify against your own service info before repair work.
- California Code of Regulations, Title 13 section 1968.2 (OBD II)malfunction criteria, section (e)
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- 2007-2016 Toyota Tundra (5.7L V8)
- 2005-2014 Nissan Murano (3.5L V6)
- 2008-2016 Honda Pilot (3.5L V6)
- 2009-2017 Ford F-150 (5.0L V8)
- 2010-2018 Chevrolet Tahoe (5.3L V8)
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