Powertrain
generic / SAE
P21B3
Closed Loop NOx Adsorber Control At Limit - Too High
NOx adsorber closed-loop trim has reached the upper authority limit — the controller cannot correct further. Typically a degraded LNT or stuck-rich engine condition.
SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number1 / B3
Possible causes
- LNT thermally aged 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: hard
- DIY: shop recommended
- Estimated cost: 400–3500 €
- Estimated time: 2–6 h
- Component: nox adsorber catalyst
- MIL / check engine light
- emissions-relevant
Sources
References
sae:J2012