Diesel Exhaust Fluid (Def) Components - EU5/6 And NAS Only
DEF Tank Module
| ITEM | DESCRIPTION |
|---|---|
| 1 | DEF tank module |
| 2 | DEF line heater |
The DEF tank module is located at the bottom of the DEF tank. The DEF tank module includes a DEF level and temperature sensor and a heater element to defrost the DEF in extreme cold climates.
The DEF level sensor is an ultrasonic device located in the DEF tank module, which sends the DEF level value to the PCM via PWM signals. The Negative Temperature Coefficient (NTC) temperature sensor measures the temperature of the fluid in the DEF tank. Similar to the ultrasonic DEF Level sensor, the temperature sensor transmits the initial temperature signal to an evaluation unit in the tank module, where the signal is converted into a PWM signal and sent to the PCM for processing.
The heater element is a Positive Temperature Coefficient (PTC) type heater. Under normal operation the maximum current is 6A. The heater element is designed to defrost the DEF in extreme cold climates. The element is a Positive Temperature Coefficient (PTC) heater that is intrinsically safe to operate. A feature of this design is that the current drawn from the electrical power supply reduces as the temperature of the element increases.
The DEF tank module receives a 12V power supply from a DEF relay located in the Rear Junction Box (RJB). The DEF relay is controlled by the PCM via power supplied from the PCM relay in the Engine Junction Box (EJB).
The PCM controls the DEF injection pump which comprises two solenoid pumps within the DEF tank. One pump supplies pressurized DEF to the DEF injector. The second pump purges DEF from the DEF injector supply line to prevent freezing in cold climates. Both pumps are controlled by a ground connection from the PCM.
The DEF tank module also supplies a controlled ground for the DEF fluid line heater. The DEF line heater receives a power supply from the DEF heater control unit and provides heating of the DEF as it passes from the DEF tank to the DEF injector in cold conditions.
DEF Heater Control Unit
The DEF heater control unit is located in the luggage compartment, adjacent to the primary battery. The control unit receives a permanent 12V battery supply via the Battery Junction Box (BJB) and the Rear Junction Box (RJB).
The DEF heater control unit provides current information for each heater power stage on a private Controller Area Network (CAN) bus to the PCM. Any faults detected are stored in the PCM fault memory and can be retrieved with an approved diagnostic system.
The DEF line heater receives a power supply from the DEF heater control unit and provides heating of the DEF as it passes from the DEF tank to the DEF injector in cold conditions.
DEF Injector
The DEF injector is located in the exhaust system, downstream of the Diesel Particulate Filter (DPF) and delivers a metered amount of DEF into the exhaust pipe.
The DEF injector works at high pressures to provide complete atomization of the injected DEF. This ensures the Selective Catalyst Reduction (SCR) catalytic converter performs at its optimum performance.
The DEF injector is activated by a PWM signal, controlled by the PCM. A signal duty cycle of 3.33 - 4 Hz determines the opening duration of the injector. The injector is designed to operate at a nominal operating pressure of 4.4 and 8.6 bar (64 and 125 psi).
Heat, generated by the exhaust system, is dissipated through the injector by cooling fins built into the body of the injector.