Code Definition

P2251 — O2 Sensor Negative Current Control Circuit / Open Bank 1 Sensor 1

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P2251

P2251 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P2251 is stored, the module has detected an open (broken or disconnected) electrical path in the monitored circuit; a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P2251 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

This code belongs to the wide band (air fuel ratio) oxygen sensor fitted upstream of the catalytic converter on the bank containing cylinder number one. Unlike a conventional narrow band sensor that simply outputs a switching voltage, a wide band sensor uses a pump cell and a reference (Nernst) cell, and the engine control module actively drives current through the pump cell to hold the measuring chamber at a stoichiometric reference point. The current required to do that is what the module converts into a lambda value. P2251 sets when the module cannot control the negative side of that pump c...

Join TaT to view the complete code information and diagnostic details.

Quick Facts