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 on 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. To determine the DEF concentration, the DEF Quality Sensor uses an internal temperature sensor to measure the temperature of the DEF. After a cold soak and after the engine is initially started, the PCM compares the temperature reading of the DEF Quality Sensor to the Intake Manifold and Coolant Temperature readings. The PCM will illuminate the MIL after the diagnostic runs and fails in 2 consecutive drive cycles. The PCM will turn off the MIL when the diagnostic runs and passes in three consecutive drive cycles.