P225A: Ford NOx sensor 1 calibration memory fails its CRC check

Ford's P225A monitor checks calibration-memory integrity in the bank 1 sensor 1 NOx controller. The stated failure criterion is that the memory does not pass its cyclic-redundancy check. This concerns the reliability of stored calibration data, rather than a measured exhaust NOx concentration exceeding a limit.

A different fault from catalyst efficiency

The NOx sensor and its controller supply information used elsewhere in exhaust aftertreatment diagnosis. If the stored sensor calibration fails its integrity check, the code does not independently demonstrate that the SCR catalyst is ineffective. Keep measurement-system faults separate from conclusions about exhaust conversion.

The source lists continuous execution and five seconds to register a malfunction. P06EA appears in the same section but covers broader processor and internal sensing-circuit problems; P225A is the more specific calibration-memory result.

What to verify

Confirm that the fault belongs to sensor 1's controller and the correct certification-specific exhaust layout. Ford notes different upstream placements for chassis- and dynamometer-certified systems. The OBD summary does not prescribe a software update, reflash or module replacement as the universal remedy. Use the application-specific service information to evaluate the stored fault and determine the approved repair and verification method.

Source and applicability

Ford 2015 model-year diesel OBD system operation summary, revision December 22, 2014; the cited monitor only, without blanket model or engine applicability. Ford source, physical PDF page 42. The documented monitor explains the fault decision; vehicle-specific service information is still needed for connector identification and a complete repair procedure.