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P221B Powertrain

NOx Sensor 1/2 Correlation (Bank 2)

NOx sensors 1 and 2 on bank 2 disagree by more than the allowed tolerance over a drive cycle. One sensor drifts, or there is a real NOx gradient that exceeds the calibrated map.

Affected components

  • Nox sensor

Common causes

  • High likelihood: One sensor drifts

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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