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P codepowertrainMedium severity

P2250O2 Sensor Reference Voltage Circuit High (Bank 2 Sensor 1)

The reference voltage circuit for the Bank 2 upstream wideband air-fuel ratio sensor is reading higher than its allowed range, so the PCM cannot trust that bank's mixture reading.

Definition

Wideband air-fuel ratio sensors use an internal reference (Nernst) cell voltage that the PCM monitors to interpret the pumping current as an air-fuel ratio. When the Bank 2 Sensor 1 reference voltage circuit exceeds its calibrated upper limit — from a short to voltage, an open circuit, or internal sensor failure — the PCM sets P2250 and typically drops that bank to open-loop or default fuel control. Symptoms include an illuminated MIL, degraded fuel economy, possible rough running or surging on Bank 2, and a failed emissions inspection.

Common causes

  • Failed wideband air-fuel ratio sensor at Bank 2 Sensor 1
  • Reference circuit wire shorted to battery or 5-volt supply voltage
  • Open circuit or high resistance in the reference wire or its connector
  • Corrosion or water intrusion in the sensor connector
  • PCM sensor interface fault (rare)

Common misdiagnoses

  • Bank 1 sensor replaced instead of the Bank 2 sensor
  • Catalytic converter blamed for Bank 2 fuel-trim symptoms
  • Fuel injectors replaced for a rich/lean condition that is only a sensor circuit fault
  • Generic narrowband O2 sensor installed in place of the required wideband part

Troubleshooting steps

  1. 1.Verify the fault with scan data

    Watch the B2S1 lambda/equivalence ratio PID — a value frozen at a default (often 1.0) while Bank 1 responds normally points to the Bank 2 sensor circuit.

  2. 2.Inspect the B2S1 connector and harness

    Bank 2 harness runs often cross the engine near heat sources; look for melted insulation, chafing, and corroded terminals.

  3. 3.Check the reference circuit for shorts to voltage

    With key on and the sensor unplugged, the reference wire should not carry battery or 5 V supply voltage per the wiring diagram values; unexpected voltage means a harness short.

  4. 4.Verify circuit continuity to the PCM

    With both ends disconnected, confirm the reference wire reads near zero ohms end to end and is isolated from adjacent circuits.

  5. 5.Replace the sensor with the correct calibration and confirm

    Install the OE-specified wideband sensor, clear codes, and verify Bank 2 returns to closed loop with active short-term fuel trim.

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