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) Pressure Sensor is a three wire sensor, integrated into the DEF Supply Pump and is not serviceable separate from the pump. The DEF Pressure Sensor monitors supply pressure to the DEF Injector. The Diesel Exhaust Fluid (DEF) Dosing Control Unit provides a 5-Volt Supply and a ground to the DEF Pressure Sensor. The sensor provides a signal to the DEF Dosing Control Unit on the DEF Pressure Sensor Signal circuit. This DEF Pressure Sensor Signal voltage changes, based on the diesel exhaust fluid pressure supplied by the DEF Supply Pump. The DEF Dosing Control Unit uses this information to vary pump speed and maintain the 130 psi (9 bar) pressure needed for proper DEF injection. The DEF Dosing Control Unit will detect a low signal voltage at low diesel exhaust fluid pressures, and a high signal voltage at high diesel exhaust fluid pressures. The DEF Dosing Control Module will illuminate the MIL light via the Powertrain Control Module (PCM) immediately after the diagnostics runs and fails. The DEF Dosing Control Module will turn off the MIL light via the PCM when the monitor runs and passes in three consecutive key cycles.