P2251 Code: O2 Sensor Negative Current Control Circuit / Open Bank 1 Sensor 1

The oxygen sensor measures the amount of oxygen in the exhaust gasses released by the engine after combustion. It sends its readings to the powertrain control module (PCM), which uses the information to adjust various processes.

If the oxygen sensor fails or stops sending its signals, the PCM might log a P2251 code.

What Does the P2251 Code Mean?

Diagnostic trouble code (DTC) P2251 stands for “Oxygen Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1.”

The PCM files this code when it detects a negative current error in the upstream oxygen sensor for engine bank one. The upstream sensor is located before the catalytic converter, while the engine bank one contains the number one cylinder.

Heated oxygen sensors are located at strategic points in the exhaust system. They have a heating element that runs on battery voltage. When the engine is cold, the heater raises the temperature of its sensor until the device can start measuring the oxygen content in the exhaust gasses.

These oxygen sensors send voltage signal outputs to the PCM. A high voltage indicates that there’s more oxygen in the exhaust, while a low voltage represents the opposite. These signals use less than one volt.

If the signal’s output does not fit within the expected range, the computer will log a P2251 code.

Note: The definition of code P2251 can differ according to the vehicle manufacturer. Check the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P2251 Code?

• Exhaust leak
• Bad oxygen sensor
• Faulty PCM
• Oxygen sensor wiring problems

What are the Common Symptoms of the P2251 Code?

• Illuminated check engine light
• Engine performance problems, such as rough running and poor acceleration
• Higher fuel consumption

How to Diagnose the P2251 Code

The P2251 code is a generic diagnostic code that various makes and models can log. However, this does not mean that there is a one-size-fits-all solution to determine the problem that’s causing it.

If you’re not confident about conducting diagnostic tests on your vehicle, it’s best to leave the job to a certified mechanic. Otherwise, you can go ahead and diagnose the issue yourself. To help you get started, here is a video that can give you an idea of what the process might involve:

How to Fix the P2251 Code

Attempting to fix a P2251 code can be difficult if you don’t have the right tools and know-how. When in doubt, take your vehicle to an auto repair shop and let the pros resolve the issue.

But if you’re an experienced automotive DIYer and you have the tools to get the job done, you can go ahead and address the P2251 code on your own. Make sure you consult a vehicle-specific repair manual or an online repair database before you get started.