P2204: NOx signal validity requires supply and communication checks

P2204 is cataloged as an intermittent NOx sensor circuit fault. Mazda's SKYACTIV-D page describes continuous validity monitoring of the NOx signal and includes the sensor electronics, its supply and supporting temperature information.

Limits of this source's numeric table

The published detection text contains an unclear speed comparison and an implausible exhaust-temperature lower limit. Those items are not reliable enough to repeat as calibration specifications. The supported diagnostic lesson is that signal validity depends on operating conditions, sensor heating and communication, rather than the DTC proving a failed sensing element by itself.

Mazda checks P2200 and U029D before continuing. Its component sequence includes exhaust gas temperature sensor number 4, the NOx sensor connection and the sensor, then SCR relay and fuse/supply checks, ground continuity and CAN wiring. A sensor deprived of supply or communication can produce unusable information without proving contamination or aging of the sensor element.

Confirmation needs the applicable emissions procedure

The source lists a remaining-distance restriction as the fail-safe. Its confirmation involves controlled DPF regeneration and subsequent idling, which require professional assessment of whether regeneration is appropriate and permitted.

Use current vehicle-specific service information for the uncertain detection limits. Preserve the full NOx and communication code set, and separate a verified electrical fault from a suspected internal sensor failure before making a replacement decision.

Documented application

Mazda3 workshop manual 01/2019 onward, d9n1-1a-22d_ver10; PCM (SKYACTIV-D). Verify exact vehicle specification; this is a Mazda application example. Mazda factory diagnostic page, mirrored by CHARM.