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Diagnostic trouble codes (DTCs) are set when there’s a problem with your car. The codes fall under four categories: powertrain, body, chassis, and network connection. Those starting with “P” are classified under the powertrain category and are often set when there’s a mechanical or electrical failure with various systems involving the engine or transmission.

Fixing a code is not easy, as it requires a deep understanding of the issue. If your scan tool registered the P0151 code, this guide will provide you with the essential things you should know for troubleshooting.

What Does the P0151 Code Mean?

Diagnostic trouble code (DTC) P0151 stands for “O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1). It means that the oxygen sensor’s voltage has remained lower than factory specifications for a certain amount of time.

Man hold in hand faulty old oxygen sensor of exhaust system focused view
P0151 code warns about a fault with the upstream oxygen sensor on Bank 2.

The code P0151 is similar to P0136, P0137, and P0131. This code warns about a fault with the upstream oxygen sensor on Bank 2. Bank 2 Sensor 1 is tucked in front of the catalytic converter. It analyzes the amount of oxygen in the exhaust before it enters the catalytic converter. The PCM uses this information to adjust the vehicle’s air-fuel ratio.

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Since the upstream O2 sensor is the primary feedback for fuel control, there may be other codes stored along with P0151, and the engine may remain in open loop as a result.

To improve emissions, car manufacturers equip cars with three-way catalytic converters, which recombines toxic compounds into safer emissions through a chemical process.

The PCM constantly tests the catalytic converter by comparing the voltage signals of the upstream and downstream O2 sensors. If the system detects that the upstream sensor’s signal is lower than specifications, it recognizes it as “O2 Sensor Circuit Low Voltage.” The PCM will immediately illuminate the check engine light and set the P0151 code.

You can find more helpful technical information in our in-depth discussion about oxygen sensors and DTCs.

Note: The definition of code P0151 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Possible Causes of Code P0151?

There are multiple factors that could cause the activation of the engine code P0151. Below are its most likely causes:

  • A faulty front O2 sensor (bank 2)
  • An issue with the O2 sensor’s circuit
  • A lean running condition
  • An exhaust leak
See also  P0132: Oxygen Sensor Circuit High Voltage (Bank 1, Sensor 1)

What are the Common Symptoms of the P0151 Code?

If you’re reading the P0151 code on your OBD scanner, you have a high chance of experiencing these symptoms:

How to Diagnose the P0151 Code

There are different ways of diagnosing the OBD code P0151 as there different causes that could trigger it. There is no universal diagnosis as cars are not built to look and operate the same. It would be very helpful to consider consulting a certified mechanic for you to avoid committing expensive mistakes.

How to Fix the P0151 Code

Clearing the P0151 code can be challenging as there are various causes and symptoms. If you don’t have the proper DIY skills and knowledge about the code, it is recommended that you let licensed mechanics handle the job for you.

If you’re confident of your knowledge about this specific DTC code, you can address it by using online auto repair resources and guides like ALLDATA. An ALLDATA subscription will give you access to a huge database of information about various faults in your vehicle. Remember to verify key information about your vehicle before proceeding to diagnostics and troubleshooting using the repair manual.

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Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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