View source for P20EE/008430

__FORCETOC__
== P20EE/008430 - SCR NOx Catalyst Bank 1: Efficiency too Low ==


== Possible Symptoms ==
* MIL (Malfunction Indicator Lamp) ON
* Loss of power (limp mode) possible
* Increased emissions
* DTC stored in ECM


== Possible Causes ==
* SCR NOx Catalyst efficiency below threshold
* Faulty NOx sensor(s) (upstream or downstream)
* Faulty Reducing Agent Injector -N474-
* Reducing Agent (AdBlue®) quality concern
* Incorrect dosing of reducing agent
* Exhaust leaks upstream of SCR Catalyst
* Catalyst temperature not within range
* DPF regeneration status interfering with monitoring


== Possible Solutions ==
* If a NOx sensor DTC is also present, diagnose that DTC first
* Check Reducing Agent (AdBlue®) quality  
* Check NOx Sensor Control Modules  
* Check Reducing Agent Injector -N474- https://forums.ross-tech.com/index.php?threads/18568/  
* Inspect for exhaust leaks before SCR catalyst
* Verify AdBlue system operation and dosing
* Perform basic settings / adaptations as per factory repair manual
* Replace SCR catalyst if efficiency cannot be restored


== Special Notes ==
* Criteria for Monitoring (as per the offical rapair manuals)
**  Difference between calculated and measured efficiency > 0.3 [-]
**  Status NOx sensor downstream = ready
**  Status NOx sensor upstream = ready
**  Urea dosing = active
**  Adaptation = not active
**  DPF regeneration = not active
**  SCR Catalyst temp gradient < 0.2 – 0.34 K/s
**  SCR catalyst modeled temp = 240 – 350 °C
**  NOx concentration upstream < 1,500 ppm
**  Integrated NOx mass flow upstream ≥ 0.4 g
* If AdBlue® is contaminated or incorrect concentration, system performance may be affected. Always use fresh, correct specification AdBlue®.
* If conditions for monitoring are not met (temperature, regeneration status, etc.), efficiency check may not run.