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.

The Diesel Exhaust Fluid (DEF) Purge Valve is housed inside the DEF Supply Pump and is not serviceable separately. The power supply and control circuits are controlled by the DEF Dosing Control Unit. The DEF Dosing Control Unit uses the DEF Purge Valve to control the direction of the fluid flow in the DEF system. The Purge Valve position determines where diesel exhaust fluid will flow as it exits the DEF Supply Pump Assembly. The diesel exhaust fluid is pumped out of the lines and back to the tank at engine shut down to prevent the fluid from freezing in the lines. The DEF Dosing Control Unit will illuminate the MIL light via the Powertrain Control Module (PCM) immediately after the diagnostics runs and fails. The DEF Dosing Control Unit will turn off the MIL light via the PCM after the monitor runs and passes for three consecutive key cycles.