P0157Powertrain
Powertrain · SAE
O2 Sensor Circuit Low Voltage — Bank 2, Sensor 2
Meaning
The downstream oxygen sensor on Bank 2 reports a voltage that is consistently below the normal operating range (below approximately 0.1 V). This may indicate a lean exhaust condition past the catalyst, an open circuit, or a short to ground.
Common causes
- Short circuit of the signal wire to ground in the sensor wiring
- Faulty O2 sensor (Bank 2, Sensor 2) with internal short
- Fuel lean condition or excessive air on Bank 2 downstream of the catalyst
- Oxidised connector with high contact resistance
- Failed heater circuit keeping the sensor below operating temperature
- Unmetered air entry into the exhaust system downstream of the catalyst
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Possible increase in fuel consumption
- Potentially elevated emissions if a lean condition is the root cause
- No noticeable driveability symptoms in case of simple sensor failure
Severity
Moderata: The vehicle is generally driveable, but the persistent low-voltage condition prevents correct catalyst monitoring and may mask mixture problems; prompt diagnosis is required.
What to do
- Inspect the wiring of O2 sensor Bank 2 Sensor 2 for shorts to ground or damaged conductors
- Measure signal voltage at the sensor connector with the engine warm and running
- Check the resistance of the sensor heater circuit to confirm it is functional
- Rule out exhaust leaks downstream of the catalyst on Bank 2
- Replace the O2 sensor if the wiring is intact and the voltage remains abnormally low