Error Code P0151: Oxygen O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)

Error Code P0151 is defined as Oxygen Sensor Circuit Low Voltage Bank 2 Sensor 1. This error code shows up when the PCM (powertrain control module, also known as ECM or engine control module in other makes) determines that the voltage given by the sensor is lower than the specified limit, or fails to improve the voltage output more than 0.21V, which indicates excessive oxygen in the exhaust.

It’s a generic trouble code, meaning, it applies to all vehicles equipped with OBD-II, from 1996 to present. Specifications on details and troubleshooting may vary depending on the make or model of the vehicle.

Definition

Error Code P0151 is triggered to track the time the Air Fuel Ratio sensor or O2 sensor takes to go from determining that the fuel control system is in open loop and rapidly switch above and below 450-millivolt set point, which indicates that the fuel control system is in closed loop. Thus, when there is a sustained low voltage signal from the O2 sensor for a specified amount of time, the Error Code P0151 is set.

Common Symptoms

As with other error codes, this one obviously triggers the Check Engine light, aside from that, the low voltage in the O2 sensor causes the PCM to enriched mixture in to the engine.

  • Exhaust leaks before or near the oxygen sensor in question. Additional leaks will be found in cold engines, and will decrease as the engine warms up.
  • Excessive fuel consumption
  • Excessive smoke coming out of the exhaust

Possible Causes

Error Code P0151 may be caused by one or more of the following:

  • Faulty oxygen sensor
  • Short to voltage on oxygen signal circuit
  • Open or high resistance on oxygen signal circuit
  • Exhaust leaks in the sensor which causes the oxygen sensor to read excessive O2 level, and the PCM to run rich

How to Check

Diagnose this error code by scanning the codes and documenting the freeze frame data and then clear the codes to verify the failure.

Then, check and monitor the oxygen sensor data to see whether the voltage switches back and forth between low and high and at a fast rate relevant to other sensors.

Check the wiring and harness connections of the O2 sensor for signs of corrosions in the connection.

Look for signs of physical damage or fluid contamination on the sensor, and repair any damages, especially leaks before replacing the O2 sensor.

Check for leaks in the exhaust and repair as necessary before retesting the sensor.

How to Fix

Repairs for this error code are pretty simple and straightforward. Obviously, faulty sensors must be replaced. Make sure you conduct a thorough diagnosis and tests to pin point a failed sensor.

  • Open, short or high resistance in the oxygen signal circuit must be repaired.
  • Damaged and faulty wirings in the bank 2 sensor 1 must be repaired, if not replaced.
  • Repair all exhaust leaks before the sensor, as they introduce excessive level of oxygen to the exhaust.

Exhaust leaks may result to voltage output from the O2 sensor, causing the O2 sensor to give low output voltage, indicating high O2 in the exhaust stream.

The PCM will not be able to control the engine’s fuel-to-air ratio if the O2 sensor is having problems, resulting in excessive fuel consumption, while excessive fuel will foul the spark plugs over time.

Check the oil and coolant leaks that may contaminate or foul the sensors.

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