P2203
NOx Sensor Circuit High (Bank 1)
The NOx sensor signal on bank 1 is above the upper limit — short to supply, open ground, or a sensor that failed high. SCR control runs in default mode.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Common causes
Ordered by how often each turns out to be the cause.
- Signal wire shorted to supplyCommon
- Sensor failed highPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- NOX Sensor
- NOX Sensor Wiring
P2203 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.