Powertrain
generic / SAE
P21B2
Excessive Time To Enter Closed Loop NOx Adsorber Control
The NOx adsorber control did not enter closed-loop operation within the calibrated time after engine start — typically a slow-warming NOx sensor or pre-heat heater fault.
SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number1 / B2
Possible causes
- NOx sensor heater weak high
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)
Inspection / repair
- Difficulty: medium
- DIY: shop recommended
- Estimated cost: 200–1500 €
- Estimated time: 1–4 h
- Component: nox adsorber catalyst
- Component: nox sensor
- MIL / check engine light
- emissions-relevant
Sources
References
sae:J2012