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P0151 OBD-II Trouble Code: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)

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P0151 code definition

O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)

What the P0151 code means

P0151 is the OBD-II generic code indicating the O2 sensor for bank 2 sensor 1 fails to increase the voltage output above .21 volts, indicating excessive oxygen in the exhaust.

What causes the P0151 code?

  • The Engine Control Module (ECM) sees the voltage of the O2 sensor for bank 2 sensor 1 below .21 volts when the ECM has commanded the fuel to a targeted rich condition on that bank of the engine.

  • Exhaust leaks before the sensor introduce excessive oxygen into the exhaust, causing the O2 sensor to read excessive oxygen, and the ECM to run rich.

What are the symptoms of the P0151 code?

  • The O2 sensor low voltage causes the ECM to enrichen the mixture into the engine.

  • The Check Engine Light will be illuminated.

  • You may have exhaust leaks before or near the O2 sensor in question. The exhaust leaks may be more when the engine is cold, and decrease as the engine warms up.

How does a mechanic diagnose the P0151 code?

  • Scans codes and documents freeze frame data then clear codes to verify failure

  • Monitors O2 sensor data to see if the voltage is switching back and forth between low and high at a fast rate compared to other sensors

  • Checks the O2 sensor wiring and the harness connections for any corrosion in the connections

  • Checks the O2 sensor for any physical damage or fluid contamination; repairs any leaks before replacing O2 sensor

  • Checks for exhaust leaks before the sensor, repairs leaks, and retests sensor

Common mistakes when diagnosing the P0151 code

Follow these simple guidelines to prevent misdiagnosis:

  • Repair any exhaust leaks before the sensor to prevent excess oxygen getting into the exhaust stream, causing the low voltage readings.

  • Repair oil or coolant leaks that can contaminate or can foul the sensors.

How serious is the P0151 code?

  • The voltage output from the O2 sensor may be due to exhaust leaks causing the O2 sensors to give low output voltages indicating excessive oxygen in the exhaust stream.

  • The ECM cannot control the fuel to air ratio of the engine if the O2 sensor is malfunctioning. This will cause poor fuel mileage, and the excessive fuel will foul spark plugs over time..

What repairs can fix the P0151 code?

  • Replacing the O2 sensor for bank 2 sensor 1 if all tests indicate a failed sensor

  • Repairing or replacing the wiring or connection to the O2 sensor for bank 2 sensor 1

  • Repairing exhaust leaks before the sensor that introduce excessive oxygen into the exhaust

Additional comments for consideration regarding the P0151 code

The O2 sensor circuit for bank 2 sensor 1 is used to give a voltage feedback to the ECM showing how much oxygen is in the exhaust stream to help the engine control the air to fuel ratio. The low voltage condition indicates excessive oxygen in the exhaust.

Need help with a P0151 code?

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