P2BAA
NOx Sensor Range/Performance (Bank 1, Sensor 1)
The upstream NOx sensor on bank 1 returns values that are not plausible for the current operating point. NOx sensors are slow to warm up, sensitive to soot and water, and are a frequent failure on diesel SCR systems.
- 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 element failedCommon
- Sensor contaminated with soot or condensatePossible
- Sensor element aged beyond calibration windowLess likely
Parts involved
- NOX Sensor Upstream
- NOX Sensor Wiring
P2BAA 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.