Theory Of Operation

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 will fail if the DEF Quality Sensor detects an internal error or an inability to supply the correct voltage to the sensing element. This diagnostic runs continuously with the key on, and the PCM will illuminate the MIL after the diagnostic fails in two consecutive drive cycles. The PCM will turn off the MIL when the diagnostic runs and passes in three consecutive drive cycles.