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 aftertreatment system is equipped with two Oxides of Nitrogen (NOx) Sensors. The upstream NOx Sensor 1/1 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 is located at the outlet of the Selective Catalytic Reduction (SCR) Catalyst and is permanently connected to a corresponding NOx Sensor Module which is mounted on the right frame rail. The NOx Sensor Probes should never be detached from it's corresponding NOx Sensor Modules. The upstream and downstream NOx Sensors are not interchangeable. The NOx Sensor Modules are smart devices and communicate with the Powertrain Control Module (PCM) over the J1939 Data Link CAN Bus. 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 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.

The aftertreatment system is equipped with two Nox Sensors and modules. The upstream NOx Sensor 1/1 is located before the SCR Catalyst and is permanently connected to a corresponding Nox Sensor Module mounted on the right frame rail. The downstream NOx Sensor 1/2 is located at the outlet of the SCR Catalyst and is permanently connected to a corresponding Nox Sensor Module also mounted on the right frame rail. The NOx Sensors and NOx Sensor Modules are calibrated to each other and must be replaced as an assembly. The two NOx Sensor and Module assemblies are not interchangeable. The NOx Sensor Modules are smart devices and communicate with the Powertrain Control Module (PCM) over the J1939 Data Link. 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. The PCM will illuminate the MIL lamp immediately after the monitor runs and fails. The PCM will turn off the MIL Lamp after the monitor runs and passes for three consecutive trips.