P2201
NOx Sensor Range/Performance (Bank 1)
The bank 1 NOx sensor reports values outside the plausibility window against modeled NOx and the downstream sensor. Often slow response from contamination by oil ash or coolant.
- 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.
- NOx sensor aged — slow responseCommon
- Sensor element contaminatedPossible
- Sensor element aged beyond calibration windowLess likely
Parts involved
- NOX Sensor
P2201 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.