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) 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 monitors the DEF concentration, and the PCM will have the Electronic Vehicle Information Center (EVIC) display a warning message based on what the DEF Quality Sensor detects. "Incorrect DEF Detected See Dealer" will be displayed if the DEF Quality Sensor detects the DEF concentration has fallen below normal. "Service DEF System See Dealer" will be displayed if something other than a DEF concentration error has been detected, or if the sensor is unable to determine the DEF concentration value. Either message will be displayed when this monitor runs and fails in one trip, and the PCM will illuminate the MIL when the diagnostic runs and fails in two consecutive drive cycles. Once the monitor runs and fails, the PCM will then run the monitor continuously until a pass decision can be made. The PCM will turn off the MIL when the diagnostic runs and passes in three consecutive drive cycles, and will only turn off the EVIC message when the monitor runs and passes, or the PCM is reflashed. Clearing the code will not erase the message.