LI49.20-N-076565

Check engine light with fault code P300E3B in the CDI control unit CDI (N3/28) Complaint Check engine light is illuminated with fault code P300E3B “The efficiency of component 'SCR catalytic converter' is not sufficient" stored in the CDI control unit (N3/28). Cause Excessive ammonia slip is being detected in the SCR system, often triggered by IUMPR (In-Use Monitor Performance Ratio) thresholds. This typically indicates that the SCR catalyst is not converting DEF (AdBlue) efficiently under moni- tored conditions. Common Driving Scenario:
•Non-dynamic driving (e.g., highway cruising with cruise control set)
•Minimal load changes, steady-state exhaust flow Contributing Factors:
•Software influence – IUMPR (In-Use Monitor Performance Ratio) thresholds
•DEF Overdosing – Over-injection due to faulty NOx sensors, dosing valve issues, or poor DEF quality
•Low Exhaust or Catalyst Temperatures – Common under low-load conditions; reduces SCR conversion efficiency
•Catalyst Degradation or Contamination – Aging catalyst or contamination from oil, coolant, or poor-quality DEF Remedy IMPORTANT: Do not replace any components unless instructed through TIPS. For Model Year 2019–2021 Vehicles:
•Update the following control units to the latest available software: N3/28 – Motor Electronics 'CDI61NFZ' for combustion engine 'OM642' (CDI):