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

P2251: O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1 — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1. Basic catalogue definition; diagnostic details have not yet been reviewed.

Affected system: Powertrain

Symptoms

  • The engine warning lamp may illuminate when the oxygen-sensor control circuit at bank 1 sensor 1 is open.
  • Fuel consumption may rise while the sensor feedback is unreliable.
  • Hesitation or rough running is possible, although the warning light may be the only symptom.

Possible causes

  • A defective or degraded upstream oxygen sensor at bank 1 sensor 1.
  • A disconnected plug, damaged wires or corroded sensor contacts.
  • An exhaust leak near the sensor may affect the signal; this does not in itself confirm a circuit failure.

What to check

  • Confirm P2251 and any other stored faults; locate bank 1 sensor 1.
  • Examine the sensor connector and nearby wiring for loose pins, corrosion and heat damage.
  • Check the exhaust near the sensor for leaks.
  • Review live sensor data and test circuit continuity against vehicle-specific service information before considering a sensor or control-module replacement.

Also written as: P2251-00, P225100 (some scan tools add the fault-type byte, e.g. -00).