Code result
P205F
Reductant System Performance
High severity
What it means
The DEF system as a whole on bank 2 is not delivering the required NOx reduction — NOx-out remains too high relative to commanded dosing across a drive cycle. Causes range from poor DEF quality, restricted dosing line, weak pump, to a degraded SCR catalyst.
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
Poor DEF quality — diluted or contaminated
highOne of the most commonly reported causes for this code — check this first.
SCR catalyst thermally aged
mediumA plausible cause — test and verify before replacing parts.
Crystallisation restricts dosing line
mediumA plausible cause — test and verify before replacing parts.
Related help
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