Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. P2251 OBD-II Trouble Code: O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1

P2251 OBD-II Trouble Code: O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1

P2251 code definition

O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1

What the P2251 code means

P2251 is an OBD-II generic code. The engine control module (ECM) monitors the negative current control of the O2 sensor heater circuit. If the current cannot be controlled and the voltage does not change on the return wire, then the ECM detects this as an open circuit in the heater circuit for the O2 sensor heater circuit.

What causes the P2251 code?

  • The O2 sensor for bank 1 sensor 1 has an open circuit in the heater circuit.
  • A broken wire or connector for the O2 sensor
  • An open wire on the power supply circuit from the ECM to the O2 sensor heater circuit
  • An open or short on the return signal wire back to the ECM

What are the symptoms of the P2251 code?

  • The Check Engine Light will be illuminated and the code is set in ECM memory as a fault.
  • The ECM may lose control of the fuel control circuit for the O2 sensor for bank 1 sensor 1.
  • The ECM may go into failure management mode to control the fuel to the engine.
  • The engine fuel mileage will go down and the engine may have various fuel-related symptoms.

How does a mechanic diagnose the P2251 code?

  • Scans codes and documents the code in the ECM and looks at the freeze frame data for failure.

  • Measures the voltage to the O2 sensor on the heater circuit.

  • Measures the resistance of the O2 sensor heater circuit at the ECM and at the sensor and checks to see if it is at the correct specifications.

  • Checks the harness for short or broken wires.

Common mistakes when diagnosing the P2251 code?

  • Clearing ECM memory codes before checking the freeze frame data for the main failure problem, so the failure may be duplicated and repaired

  • Failing to clear the ECM codes after the codes are fixed

  • Replacing an O2 sensor without verifying the failure of the heater circuit. This could be an intermittently shorted wire in the harness

How serious is the P2251 code?

Code P2251 is major failure in the O2 sensor heater circuit and the O2 sensor may be rendered unable to respond to the exhaust O2 and cause the ECM to go into failure mode. This may cause the vehicle to fail emission testing and cause drive complaints depending on the manufacturer.

What repairs can fix the P2251 code?

Additional comments for consideration regarding the P2251 code

Code P2251 is for the O2 sensor heater circuit. This heater allows the O2 sensor to respond quicker than an O2 sensor that does not have one. This circuit is on most (if not all) model cars and light trucks since about 1990 and later.

Need help with a P2251 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
Auto Safety Tips
Driving is more than a way to get from point A to point B. Owning and driving a car can also be a highly enjoyable experience. Whether a person is driving...


Related questions

Q: I have a 1986 Chrysler Laser turbo with 13700 miles that failed emissions. Do oxygen sensors go bad from sitting around too long?

Wow, I almost bought one of these new back in 1986. It is possible that due to age, any number of sensors can be bad, even without a Check Engine Light being set. The best way to determine that is...

Q: Check engine light on, temperature goes to hot, noisy engine, car shuddring and turns off.

Fault codes need to be read out from the engine computer. There is a technical service bulletin (TSB) out by Lexus that points to a faulty thermostat causing a Check Engine Light, and that the thermostat should be replaced based...

Q: Car stalling at random, could be an electrical problem?

Generally, when the car is running consistently and on all cylinders, when stalling it is often times a fuel supply issue (or in some cases indirectly related to electrical - i.e. bad connection or pulse to the fuel injectors). I...