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.
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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
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.
-
Check for exhaust leaks between the catalytic converter and the downstream sensor on bank 2.
-
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.
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.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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