SIDECUTTER-LH 1122488 - Caterpillar

General Operation
Illustration 1 g03877485
(1) Exhaust inlet
(2) Diesel Exhaust Fluid (DEF) injector
(3) Selective Catalytic Reduction (SCR) system
(4) Exhaust out
(5) Nitrogen Oxide (NOx) sensor
(6) Diesel Particulate Filter (DPF)
(7) Diesel Exhaust Fluid (DEF) supply line
(8) Coolant return to engine line
(9) Diesel Exhaust Fluid (DEF) pump
(10) Coolant supply from engine line
(11) Coolant diverter valve
(12) Diesel Exhaust Fluid (DEF) tank
(13) Coolant supply connector
(14) Suction connector
(15) Backflow connector
(16) Coolant return connector
(17) DEF suction line
(18) DEF backflow line
(19) Diesel Exhaust Fluid (DEF) Control Unit (DCU)
(20) Electronic Control Module (ECM)The purpose of Diesel Exhaust Fluid (DEF) is to create a Selective Catalytic Reduction (SCR) process to take place in the exhaust system to reduce Nitrogen Oxides (NOx).When the engine is keyed on but not running, DEF is not being injected into the system. When the engine is running, the DEF may be too cold or frozen to be injected. When the ambient or tank temperatures are cold enough, the DEF control unit (DCU) opens the coolant diverter valve to allow engine coolant to flow through the DEF tank to warm the system. The DCU also activates the heater circuits in the lines and pump to prevent DEF from freezing in the lines and pump. The time it takes to thaw the system depends on the tank temperature. Since the system always starts with empty lines, the pump activates to fill the lines with fluid before DEF injection begins.This is called DEF Priming mode. Once the system is primed, the DEF will be injected when the DEF tank and SCR temperatures are warm enough. The DEF dosing system must be fully functional within 70 minutes following engine start-up. If DEF injection does not start within 70 minutes, a diagnostic code will become active.Note: Typical usage for DEF is 1-3% of diesel fluid.The DEF system has three operation modes:1. DEF Priming ModeSince the system always starts with empty lines, the pump activates to fill the lines with fluid before DEF injection begins. Priming will start when engine speed is greater than 450 rpm, DEF tank temp is greater than −6° C (21.2° F), and SCR inlet temperature is greater than 100° C (212° F). Once the system reads the appropriate pressures, priming is complete.2. DEF Injection ModeOnce the system is primed, the DEF will be injected when SCR inlet temperature is greater than 200° C (392° F). The DEF pump draws DEF from the tank and pressurizes the DEF to 900 kPa (130.5 psi). This pressure is constant throughout the operating cycle. The DEF injector sprays DEF into the exhaust before the SCR catalyst and continues spraying by pulsing on and off. The DEF injection rate is controlled by changing the duration of the DEF injector on time. If the engine is producing higher NOx, the DEF injector will turn on more frequently. To control the pressure to the DEF injector, a percentage of DEF will flow through the backflow line back to the tank.3. DEF Purge ModeWhen a DEF-related fault code becomes active or the engine is keyed