P23BD
NOx Sensor Performance Signal Biased or Stuck High Bank 1 Sensor 3
The NOx sensor on bank 1 sensor 3 reports a value that stays at the upper end of its range despite changing engine conditions - sensor element biased or stuck high.
- 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.
- Sensor element biased highCommon
- Sensor element aged beyond calibration windowLess likely
- Sensor element contaminated by oil, soot or coolantLess likely
Parts involved
- NOX Sensor B1s3
P23BD 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.