O2 Sensor Circuit Low Voltage Bank 2 Sensor 2
Diagnostic trouble code P0157 indicates that the powertrain control module (PCM) has detected a low voltage condition from the downstream oxygen sensor on Bank 2 (Sensor 2). This means the sensor's signal voltage remained below the acceptable threshold for a specified amount of time, suggesting a lean exhaust condition or a circuit issue.
While this code typically will not cause immediate drivability issues or strand you, it should be addressed soon to ensure proper emissions monitoring and prevent potential long-term catalytic converter damage.
Common symptoms
- Illuminated Check Engine Light
- Failed emissions test
- Slight decrease in fuel economy
- Possible rough idle
- No noticeable drivability symptoms in many cases
Likely causes
- Faulty Bank 2 Sensor 2 oxygen sensor
- Exhaust leak near the oxygen sensor
- Damaged, shorted, or corroded wiring or connectors in the O2 sensor circuit
- Lean running condition in the engine
- Faulty catalytic converter
- Powertrain Control Module (PCM) failure (rare)
What to check before replacing parts
Visually inspect the wiring and connector for the Bank 2 Sensor 2 oxygen sensor.
Look for: Look for melted, chafed, or broken wires, and check the connector for corrosion or loose pins that could cause a poor connection or short to ground.
Check for exhaust leaks near the Bank 2 Sensor 2 oxygen sensor and catalytic converter.
Look for: Listen for ticking sounds or feel for escaping exhaust gases around flanges and welds, as outside air entering the exhaust can cause a false lean (low voltage) reading.
Monitor the Bank 2 Sensor 2 voltage using a scan tool with live data.
Look for: The voltage should fluctuate slightly but generally remain steady around 0.45V to 0.8V when the engine is warm. If it stays stuck below 0.2V, the sensor or circuit is faulty.
Test the oxygen sensor heater circuit and signal circuit for proper voltage and ground.
Look for: Using a multimeter, verify that the sensor is receiving the correct reference voltage and has a solid ground. A lack of voltage or a short to ground indicates a wiring issue.
Induce a rich condition (e.g., by adding propane to the intake) while monitoring the O2 sensor voltage.
Look for: If the sensor voltage rises in response to the rich condition, the sensor is functioning and the issue may be a genuine lean condition or exhaust leak. If the voltage remains low, the sensor is likely defective.
This page explains the generic P0157 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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