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P21B5 Powertrain

NOx Adsorber Over Temperature (Bank 2)

A temperature sensor at the NOx adsorber on bank 2 reports a value above the safe limit. Sustained over-temperature destroys the storage washcoat.

Affected components

  • Nox adsorber catalyst

Common causes

  • High likelihood: Runaway desulphation regeneration

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.

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