P229F
NOx Sensor Circuit Range/Performance Bank 1 Sensor 2
The downstream NOx sensor on bank 1 (after the SCR catalyst) returns implausible NOx readings during operation. Either the sensor is degraded or upstream chemistry is abnormal.
- 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.
- NOx sensor agingCommon
- Low SCR efficiencyPossible
- Sensor element aged beyond calibration windowLess likely
Parts involved
- NOX Sensor
- SCR Catalyst
P229F 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.