Theory Of Operation

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 out of the line and back into the tank. The DEF Dosing Control Unit provides a Pulse-Width Modulated (PWM) power supply and a constant ground to the DEF supply Pump assembly to control the speed and output of the pump. The DEF Dosing Control Unit will illuminate the MIL via the Powertrain Control Module (PCM) immediately after the system detects a failure to prime after ten consecutive attempts.

The DEF Supply Pump's most common cause for failing to prime is DEF system contamination and/or ice build-up in various DEF system components.

The first warning will occur when the DTC 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.