Code result
P21B3
Closed Loop NOx Adsorber Control At Limit - Too High
Moderate severity
What it means
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.
Is it safe to drive?
Use caution
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.
Most likely causes
LNT thermally aged
highOne of the most commonly reported causes for this code — check this first.
Related help
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