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P codepowertrainMedium severity

P2203NOx Sensor Circuit High Input (Bank 1)

The Bank 1 NOx sensor signal circuit is reading above its expected voltage range, usually from a short to voltage or an internal sensor failure.

Definition

The control module continuously checks the plausibility of the Bank 1 NOx sensor signal, which is used to control SCR/DEF dosing and verify NOx reduction. P2203 sets when the signal circuit voltage exceeds the maximum expected threshold, indicating a short to battery voltage, connector damage, or a failed sensor element or integrated sensor module. The MIL will illuminate, NOx-based closed-loop dosing may be suspended, and on diesel applications a persistent fault can start the SCR inducement countdown toward torque or speed derate.

Common causes

  • Failed NOx sensor or its integrated control module
  • Signal wiring shorted to battery or reference voltage
  • Connector terminal damage or corrosion causing erratic high readings
  • Water intrusion into the sensor module or connector
  • Exhaust leak upstream skewing the sensor's oxygen reference
  • Aftermarket electrical work pinching the harness

Common misdiagnoses

  • SCR catalyst
  • DEF injector/doser
  • Oxygen sensor replaced instead of the NOx sensor
  • PCM/ECM replacement without circuit testing

Troubleshooting steps

  1. 1.Pull codes from all modules and review data

    Compare Bank 1 NOx ppm readings against Bank 2 or expected values at idle; a pegged-high or fixed reading confirms the circuit or sensor fault.

  2. 2.Inspect wiring for shorts to voltage

    Look for melted insulation where the harness crosses hot exhaust components or rubs against other powered circuits.

  3. 3.Load-test the sensor supply and ground

    Verify clean battery voltage and a solid ground at the sensor module connector with the circuit loaded, not just with a voltmeter on an open circuit.

  4. 4.Check for exhaust leaks ahead of the sensor

    A leak lets ambient air reach the sensing element and can drive NOx/O2 readings implausibly high; repair leaks before condemning the sensor.

  5. 5.Replace the NOx sensor if wiring is verified

    Fit an OE-calibrated sensor, clear the code, and complete the manufacturer's SCR monitor drive cycle to confirm the fix.

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