Theory Of Operation

WARNING: This page is about a different car, the 2015 RAM 3500 HD and 2015 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) controls the heater supply voltage feed to the Diesel Exhaust Fluid (DEF) Dosing Control Unit via the SCR Relay1. The DEF Tank electric heater and DEF Line Heater power supply and ground circuits are controlled by the DEF Dosing Control Unit. The DEF Tank Heater is integrated into the DEF Supply Pump Assembly and is not serviced separately.

Heating of DEF Supply Line and DEF Tank operate independent of each other. Line heating is based on the Ambient Temperature Sensor input and tank heating is based on the DEF Tank Temperature Sensor value. Heating of the line or tank heater is initiated when the corresponding temperature value is below -5°C (23°F). Heating is stopped when the corresponding temperature value goes above -4°C (24.8°F). The DEF Dosing Control Unit monitors these inputs and reports them to the Powertrain Control Module (PCM). The PCM will illuminate the MIL lamp after this diagnostic runs and fails. The PCM will turn off the MIL light when the monitor runs and passes in three consecutive key cycles.