NOx Sensor Delayed Response - High to Low Bank 1 Sensor 1
The pre-catalyst NOx sensor on bank 1 (sensor 1) reacts too slowly when NOx in the exhaust drops from a high to a low level — for example after a fuel cut or transition into low-load. Aged ceramic cells, soot deposits or condensation inside the sensor protective tube slow the diffusion of NOx to the measuring element.
Affected components
- Nox sensor b1s1
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.