NOx Sensor Delayed Response - High to Low Bank 1 Sensor 2
The post-catalyst NOx sensor on bank 1 (sensor 2) reacts too slowly when NOx in the exhaust drops from a high to a low level. Same failure mechanism as the upstream sensor — aged element, soot or condensate — but post-catalyst the consequence is a degraded SCR conversion-efficiency monitor.
Affected components
- Nox sensor b1s2
Common causes
- High likelihood: Aged sensor element with reduced response speed
- Medium likelihood: Soot clogging the protective tube
Possible 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)
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
Related codes
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.