0391306 JOHNSON COVER ASSY,Shorting switch

Illustration 1 g06172881
Typical example
(1) Exhaust inlet from back pressure valve
(2) Selective Catalytic Reduction (SCR) system
(3) Exhaust out
(4) Nitrogen Oxide (NOx) sensor
(5) Diesel Exhaust Fluid (DEF) injector
(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) Electronic Control Module (ECM)The Diesel Exhaust Fluid (DEF) Dosing Control System consists of the following components.
Pump Tank Unit (PTU)
DEF injector
DEF System Heated LinesPump Tank Unit (PTU)
The Pump Tank Unit (PTU) consists of the following components.
DEF tank
DEF pump
DEF header
Coolant diverter valveDEF Tank
The DEF tank stores the DEF. The size of the DEF tank will depend on the application.The DEF solution is made of 32.5 percent urea solution and 67.5 percent deionized water. Urea is a compound of nitrogen that turns to ammonia when heated.Ensure that the correct specification of DEF is used. Refer to Operation and Maintenance Manual for more information.DEF does degrade over time at elevated temperatures. Due to freezing risk, the tank, pump, and lines must be heated and designed to contain frozen DEF.DEF Pump
Illustration 2 g03403876
Typical example
(1) Inlet
(2) Coolant inlet
(3) Backflow
(4) Coolant outlet
(5) Outlet
(6) DEF filterThe pump supplies filtered DEF fluid to the DEF injector. The pump consists of inlet port (1) which is the suction side of the pump. The pump then pressurizes the fluid up to 896 kPa (130 psi) and supplies the fluid though outlet port (5). There is a fixed orifice within the pump that purges the pressure off the pressurized circuit. This pressure relief will stabilize the pressure in the line when the DEF injector is opening and closing.Once the engine is shut down, the pump will start to go into a purge mode. The DEF Injector will open and the reverting valve within the pump will reverse the flow of the pump and purge the pump and pressure line. This reversed flow will route any remaining DEF fluid back to the tank.The DEF inlet and backflow connectors have a 100 micron screen to filter any debris in the system.Engine coolant is routed through the pump to warm the pump during cold-weather operation.Refer to Operation and Maintenance Manual for the correct procedure to replace the DEF filter.DEF Tank Header
Illustration 3 g06132474
Typical example
(1) DEF tank header filter (32 micron)
(2) Coolant tubes
(3) DEF level sensor (float)
(4) DEF pickup tube
(5) DEF tank header filter (100 micron)
(6) DEF tank temperature sensor (integrated within DEF level sensor, not shown)
(7) DEF quality sensor
(8) DEF back flow tubeThe DEF tank header is located in the DEF tank. The tank header consists of several parts and performs the following functions:Fluid Level SensorThere is a tank level sensor to measure the amount of usable DEF in the tank. The level sensor includes a flotation device that contains a magnet. As the fluid level changes, the float slides along a shaft that contains a series of reed switches and resistors. There are multiple reed switches for different heights of the tank. The magnetic float closes the passive reed switch and completes the circuit of resistors giving a different resistance output. The tank level sensor will send a signal to the ECM to signal that the level of DEF is low. The engine may derate. The ECM then interprets the resistance to a tank level and changes the DEF gauge.DEF Pickup TubeThe DEF is pulled from the bottom of the tank through a filter.DEF Tank Header FilterAt the end of the DEF Pickup tube is a 100 micron filter to filter debris from entering the system. The filter is serviceable.DEF Tank Header FilterA 32 micron filter wraps around the coolant tubes to filter debris from entering the pickup and backflow circuits. The filter is serviceable.Coolant TubesThe coolant supplied by the engine will flow through the tubes when the coolant diverter valve opens. Coolant runs along the pickup tube to the bottom of the tank and then spirals around the level sensor. The heat from the coolant will thaw any frozen DEF in the tank or header. The heat will also prevent the DEF from freezing around the pickup tube.DEF BackflowThe pump has a backflow circuit to return DEF back to the tank. The backflow tube returns the DEF to the top of the tank.DEF Tank Temperature SensorAt the bottom of the tank header, integrated within the DEF level sensor and near the DEF tank header filter is a tank temperature sensor. The temperature sensor is a passive thermistor. The resistance of the thermistor varies with temperature. This sensor monitors the temperature of the DEF in the tank. This temperature is used to determine when to turn on the coolant diverter valve.DEF Quality SensorAt the bottom of the tank header next to the DEF tank header filter is the DEF quality sensor. The DEF quality sensor uses an optical Near Infra-Red (NIR) technology that takes measurements of urea concentration by measuring the chemical properties of the DEF solution. Based on these chemical properties and fluid temperature, the sensor is able to detect urea concentration with an accuracy of up to 2 percent. If the sensor detects the quality of DEF is not within specifications, a fault code will trip indicating the DEF concentration is not correct. The engine may derate.There is a configuration parameter in the electronic service tool called "Aftertreatment #1 DEF Quality Sensor Installation Status" that must be programmed to "Installed". The parameter is factory password protected. The DEF tank header with the DEF quality sensor is a data link type sensor. The temperature sensor and level sensor are also data link type sensors on DEF tank headers with the quality sensor.Electric Components of the PTU
The Pump Electronics Tank Unit (PTU) consists of the following components:Coolant Diverter ValveControls coolant flow to the tank and DEF pumpHeated LinesThe heated lines are electrically heated lines that will turn on any time the ambient temperature is cold. These lines will thaw frozen