Theory of Operation

WARNING: This page is about a different car, the 2011 RAM Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

This DTC is referring to the DEF Pressure Line Heater. Each of the Diesel Exhaust Fluid (DEF) system hoses has a built in heater to warm the fluid in the lines. The three line heaters share a common power supply via the DEF Line Heater Relay which is controlled by the DEF Dosing Control Unit. The DEF Dosing Control Unit controls the heaters individually through the line heater return circuits. The three line heater circuits are monitored at the return circuit. The DEF Dosing Control Unit will illuminate the MIL light via the PCM immediately after the diagnostics runs and fails and the line heater will be disabled. The DEF Dosing Control Unit will turn off the MIL light via the PCM when the monitor runs and passes in three consecutive key cycles.