Code result
P21B4
NOx Adsorber Over Temperature
High severity
What it means
A temperature sensor at the NOx adsorber on bank 1 reports a value above the safe limit. Sustained over-temperature destroys the storage washcoat.
Is it safe to drive?
No — stop driving
This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly.
Most likely causes
Runaway desulphation regeneration
highOne of the most commonly reported causes for this code — check this first.
Related help
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