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) Supply Pump Assembly has many functions. It's primary purpose is to build adequate system pressure for dosing into the exhaust. When the system is shut down the pump is used to purge the fluid to of the line and back into the tank. The DEF Dosing Control Unit provides the 12 volt supply and ground for the pump. The DEF Dosing Control Unit also provides a Pulse Width Modulated (PWM) signal to the DEF Supply Pump Assembly to control the speed and output of the pump. 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 when the monitor runs and passes in three consecutive key cycles. Note: The DEF Dosing Control Unit is located on the DEF Tank.

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.