Theory Of Operation

WARNING: This page is about a different car, the 2016 RAM 3500 HD and 2016 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.

The aftertreatment system is equipped with two NOx Sensors (2 probes and 2 modules). The upstream NOx Sensor 1/1 probe is located on the Turbocharger elbow downpipe and is permanently connected to a corresponding NOx Sensor module mounted to the hot side of the engine block. The downstream NOx Sensor 1/2 probe is located at the outlet of the SCR Catalyst and is permanently connected to a corresponding NOx Sensor module which is mounted on the right frame rail. The NOx Sensor probes and NOx Sensor modules are calibrated to each other and must be replaced as an assembly. The two NOx Sensor probe-and-module assemblies are not interchangeable. The NOx Sensor modules are smart devices and communicate with the PCM over the J1939 Data Link circuits. The NOx Sensor modules perform their own internal diagnostics and report malfunctions back to the PCM. The NOx Sensors are used to monitor the efficiency of the SCR Catalyst and dosing system. The PCM will illuminate the Malfunction Indicator Lamp (MIL) after the diagnostic runs and fails in two consecutive drive cycles. The PCM will turn off the MIL immediately after the monitor runs and passes.