P20EE
NOx Catalyst Efficiency Below Threshold
What it means
The SCR catalyst on bank 1 is no longer reducing NOx to the level the ECU expects, even with proper reductant dosing and quality. Often the result of catalyst poisoning by sulphur or hydrocarbons, thermal aging, or a leak between the upstream and downstream NOx sensors.
Is it safe to drive?
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
SCR catalyst aged or poisoned
highOne of the most commonly reported causes for this code — check this first.
NOx sensor drift
mediumA plausible cause — test and verify before replacing parts.
Exhaust leak between upstream and downstream NOx sensors
lowLess common, but worth ruling out after the more likely causes.
Related help
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