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DTC codes / P22xx · Fuel and air metering (injector circuits) / P2251
P2251 indicates that the engine control module (ECM) has detected an open or abnormal condition in the negative current control circuit for the upstream oxygen sensor on bank 1, sensor 1. The ECM monitors the sensor's heater or pump current and sets this code when the circuit does not behave as expected, often due to a wiring fault or a failed sensor.
Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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