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EmissionsSeverity Medium: diagnose soon

P2251O2 Sensor Negative Current Control Circuit/Open (Bank 1 Sensor 1)

What it means

The ECU sees an open circuit on the negative (virtual ground) wire of the upstream wide-band oxygen sensor.

Symptoms

  • Check engine light
  • Rough running or higher fuel consumption
  • Engine may run in open loop

Common causes

  • Wiring fault on that circuit of the wide-band sensor
  • Corroded connector
  • Failed wide-band oxygen sensor
  • ECU sensor interface fault (rare)

What to check first

  1. Check each wire between the sensor and ECU for continuity and shorts
  2. Check the connector for corrosion
  3. Compare with a known-good sensor's behaviour (lambda reading at idle and on overrun)
Can I drive with P2251? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

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P2251: questions and answers

What does P2251 mean?

P2251: O2 Sensor Negative Current Control Circuit/Open (Bank 1 Sensor 1). The ECU sees an open circuit on the negative (virtual ground) wire of the upstream wide-band oxygen sensor.

What are the symptoms of P2251?

Check engine light. Rough running or higher fuel consumption. Engine may run in open loop.

What causes P2251?

Wiring fault on that circuit of the wide-band sensor. Corroded connector. Failed wide-band oxygen sensor. ECU sensor interface fault (rare).

How do you diagnose P2251?

1. Check each wire between the sensor and ECU for continuity and shorts 2. Check the connector for corrosion 3. Compare with a known-good sensor's behaviour (lambda reading at idle and on overrun)

Can I drive with P2251?

Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.