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 Powertrain Control Module (PCM) uses the NOx Sensor 1/1 and NOx Sensor 1/2 feedback along with engine operating and environmental conditions to calculate the Diesel Exhaust Fluid (DEF) dosing rate. This diagnostic will fail when the PCM detects that the adjusted DEF dosing commanded rate has reached a maximum limit and the downstream, 'system out' levels (NOx Sensor 1/2) are higher than expected. The PCM will illuminate the Malfunction Indicator Lamp (MIL) after the diagnostic runs and fails in 2 consecutive drive cycles. The PCM will turn off the MIL after the diagnostic runs and passes in 3 consecutive drive cycles.