HOLDER ASSEM. 9P3436 - Caterpillar

When to overhaul your SCR:
Keep records of Fuel and DEF used:
Over the life of the catalyst a closed loop SCR system will compensate for losses in catalyst effectiveness by increasing the amount DEF being injected. You can see this trend by keeping detailed records of fuel and DEF usage over and tracking the ratio of DEF to fuel. There is not a specific condemning limit on the ratio of DEF to fuel. If you operate multiple units of the same engine configuration and SCR configuration and are governed by the same system emissions out targets, you may be able to predict your sites catalyst replacement interval by tracking DEF to Fuel ratio and calculating a percent increase in DEF to fuel ratio from initial start-up.Low NOx Conversion Alarm
Eventually the catalyst will no longer be able to meet the NOx conversion target due to normal catalyst aging and extra DEF will only result in unconsumed ammonia passing through the system. Once the closed loop control system detects that the target NOx conversion is no longer being met. The system will indicate a Low NOx Conversion Code. The Cat dealer Technician will follow the procedures in the troubleshooting guide to ensure that the system is working correctly and that overhauling the catalyst is required. This action is the best indicator that the system requires overhaul.Inspection/Cleaning of Components
Inspect the following components during aftertreatment overhaul:
Air regulator
DEF Nozzle
Dosing Cabinet
CEM Housing / Mounting Structure
Diesel Exhaust Fluid (DEF) Nozzle
Diesel Particulate Filters (DPF)
Clean Emission Module (CEM)
Dosing cabinet sensors, harness, and solenoid valvesReplacement of Components
Replace the following components during aftertreatment overhaul:
Air Strainer
SCR Catalysts
DEF Strainer
Sensor (Temp, Level, Pressure)
DEF Pump (Diaphragm and Seals)
Diesel Oxidation Catalysts (DOC)
Aftertreatment temperature and differential pressure sensors.
Dosing cabinet sensors, harness, and solenoid valves
(NOx Inlet/Outlet), temperature, and pressure sensors.