Diesel Exhaust Fluid (DEF) Tank Module

The Diesel Exhaust Fluid (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 Pulse Width Modulation (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 6 A. The heater element is designed to defrost the DEF in extreme cold climates. The element is a 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 12 V 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 2 (EJB 2).

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 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.