Skip the auto shop - Our mechanics make house calls

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

How to Buy Fuel Treatments
Adding a fuel additive to your gas tank when you fill up is one way to clean vital engine parts of deposits, improve the performance of your engine,...
Veteran and Military Driver Laws and Benefits in Idaho
The state of Idaho offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch in the...
P2159 OBD-II Trouble Code: Vehicle Speed Sensor B Range/Performance
Diagnostic Trouble Code (DTC): P2159 P2159 code definition Vehicle Speed Sensor B Range/Performance Related Trouble Codes: P2158: Vehicle Speed Sensor B P2160: Vehicle Speed Sensor B Circuit Low P2161:...


Related questions

Q: I have 05 audi a 6 Quattro 4.2. I sprayed the engine off one afternoon. Now I'm getting primary/ secondary circuit malfunction sho

This is a common problem with the Audi models. Generally one of the advantages to having coil packs instead of a distributor is that they are a little more water resistant, however this is a known issue with Audi in...

Q: What Is the Problem When the Check Engine Light Comes On?

The Check Engine Light is on most vehicles built in the last twenty years. The light is used to alert the operator of the vehicle that there is a problem that needs to be looked at as soon as possible....

Q: power shuts down,but will run and drive very slow

For issues like this you should have the system computer scanned and have any codes diagnosed by a mechanic. The cost to have the problem properly diagnosed far out weighs throwing parts at the problem hoping to fix it. The...