Theory Of Operation

WARNING: This page is about a different car, the 2019 RAM 3500 HD and 2019 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.

The Diesel Exhaust Fluid (DEF) Quality Sensor is mounted to the DEF tank and is used to detect the concentration of the DEF. The DEF Quality Sensor shares information with the Powertrain Control Module (PCM) over the J1939 Data Link. This diagnostic will fail if the datalink information between the DEF Quality Sensor and the PCM has been lost. The PCM will have the Electronic Vehicle Information Center (EVIC) display "Service DEF System See Dealer" message when this diagnostic runs and fails in one trip, and will illuminate the MIL when the diagnostic runs and fails in two consecutive drive cycles. The PCM will turn off the MIL when the diagnostic runs and passes in three consecutive drive cycles, and will turn off the "Service DEF System See Dealer" EVIC message only when the diagnostic runs and passes, or the PCM is reflashed. Clearing the code will not erase the message

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.