Theory Of Operation

WARNING: This page is about a different variant/trim than selected.

The Diesel Exhaust Fluid (DEF) pump operates in three main stages: Pressure Build, Metering Control, and Purge.

Once the SCR Catalyst reaches operating temperature of 273°F (134°C), the PCM will begin the pressure build phase. The Powertrain Control Module (PCM) will activate the DEF Supply Pump to refill the line. As the line fills, the pressure builds to the set point. The PCM turns on the DEF Injector to bleed air out of the Pressure Line. Each time the injector is turned off, the PCM monitors the amount of time it takes for the pressure to rise back to the set point to determine when all of the air is bled out of the line.

During Metering Control, the PCM adjusts pump run time to maintain a steady pressure between 6.5 - 8.5 bar (94 - 123 psi).

When the engine is shut off, the Purge pump will activate. The purpose is to draw the DEF back into the tank to protect the line. DEF will freeze at 12°F (-11°C) and its concurrent expansion has potential to damage the pressure line.

When the DEF system is in pressure control mode, the Powertrain Control Module (PCM) activates the DEF Supply Pump to refill the lines. As the lines fill, the pressure builds to the set point. When the pressure reaches the set point, the PCM turns on the DEF Injector to bleed air out of the Pressure Line. Each time the injector is turned off, the PCM monitors the amount of time it takes for the pressure to rise back to the set point to determine when all of the air is bled out of the line. The PCM will illuminate the MIL immediately after the diagnostic runs and fails and diesel exhaust fluid injection into the aftertreatment system is disabled.

The PCM also monitors the DEF pressure to provide correct system performance. If excessive air is detected during pressure buildup, the Purge Pump system draws fluid back into the DEF tank to remove the air. Once the purge is complete the pressure buildup cycle will run again.