Powertrain, generic (extended)

P225A NOx Sensor Calibration Memory (Bank 1 Sensor 1)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P225A concerns the front NOx sensor of bank 1, the one ahead of the SCR catalyst. Modern NOx probes come with their own control unit that holds a sensor-specific calibration and reports finished values over CAN; this code means the stored calibration data of that unit cannot be read or fails its check. Ford's 2014 PCM code table carries P225A as a MIL code, but no manufacturer publishes the test or a threshold. Ford's 2023 diesels report memory errors inside the NOx sensor module under P2200 instead. CARB requires NOx sensor faults to be caught when the sensor can no longer serve as a feedback or monitoring input. P225B is the same fault on the downstream sensor. Usually the sensor assembly is replaced, as its memory cannot be repaired.

Likely causes

Internal memory or checksum fault in the NOx sensor control unit
Replacement sensor with a part number or calibration that does not suit the vehicle
Supply voltage dropout or poor connector contact while the module was storing data
Engine or aftertreatment control unit software that misreads the sensor data

Symptoms

  • MIL on, usually without any change in how the engine runs
  • SCR dosing runs without valid feedback, so NOx emissions may rise
  • Follow-up NOx catalyst efficiency codes possible

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€250–900
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

nox sensor

Related codes

P225BP2200P2201P20EE

References: law.cornell.edu, performanceparts.ford.com, ni.com, fordservicecontent.com.