Theory Of Operation

When the Diesel Exhaust Fluid (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 light immediately after the diagnostics runs and fails and diesel exhaust fluid injection into the aftertreatment system is disabled.