P225C
NOx Sensor Performance - Signal Biased/Stuck High (Bank 1 Sensor 1)
NOx Sensor Performance - Signal Biased/Stuck High (Bank 1 Sensor 1): the component is electrically intact but its response does not match the command.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
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.
- Sensor poisoned by silicon, sulphur, or oil ashCommon
- Sensor element aged beyond calibration windowLess likely
- Sensor element contaminated by oil, soot or coolantLess likely
Parts involved
- NOX Sensor
P225C 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.