Theory of Operation

The DEF Pressure Sensor provides a signal to the DEF Dosing Control Unit on the sensor signal circuit. This sensor signal voltage changes based on the diesel exhaust fluid pressure supplied by the DEF Pump Assembly. The DEF Dosing Control Unit will detect a low signal voltage at low diesel exhaust fluid pressures, and high signal voltage at high diesel exhaust fluid pressures. The DEF Dosing Control Unit will illuminate the MIL light via the Powertrain Control Module (PCM) immediately after the diagnostics runs and fails and diesel exhaust fluid injection into the aftertreatment system is disabled. The DEF Dosing Control Unit will turn off the MIL light via the PCM immediately after the monitor runs and passes.