Theory Of Operation

The Diesel Exhaust Fluid (DEF) Injector is mounted to the decomposition tube at the inlet of the Selective Catalytic Reduction (SCR) Catalyst. The Powertrain Control Module (PCM) sends a Pulse Width Modulated (PWM) signal to DEF Injector to vary the amount of fluid sprayed into the exhaust stream. The PCM will illuminate the MIL lamp after this diagnostic runs and fails in two consecutive trips and diesel exhaust fluid injection into the aftertreatment system is disabled. The PCM will turn off the MIL lamp immediately after the diagnostic runs and passes for three consecutive key cycles.