Theory Of Operation

WARNING: This page is about a different car, the 2017 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.

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.

The first warning will occur when the p-code becomes pending or active. The customer will hear a chime and get an EVIC message reading "Service DEF System See Dealer." The second warning level will occur if the customer continues to drive and the code has not cleared. The customer will hear a chime and get an EVIC message reading "Speed Limited to 5 mph in XXX MILES See Dealer". Upon driving until the countdown reaches zero, the customer will hear a chime and get an EVIC message reading "5 mph Max on Restart, Long Idle or Refuel See Dealer." Upon key-off, refuel, or 1 hour long idle, the EVIC message will read, "Speed Limited to 5 mph See Dealer." Once induced to a 5 mph derate, the inducement will not clear unless the diagnostic runs and passes, or the PCM is recalibrated.