Cummins X12 CM2350 X119B (2018 & Newer) Fault Code: 3878 PID: SPN: 3364 FMI: 2 Aftertreatment Diesel Exhaust Fluid Quality- Data Erratic, Intermittent, or Incorrect

Circuit Description
The DEF quality sensor is a smart device and communicates with the engine electronic control module (ECM) via the J1939 data link. The DEF quality sensor receives power and ground directly from the battery. The sensor performs its own internal diagnostics and reports malfunctions back to the primary engine ECM via the J1939 data link. The DEF quality sensor is used to measure the concentration of the DEF in the tank.

Component Location
The DEF quality sensor is typically mounted in the DEF tank or in-line with the DEF dosing unit supply line. Reference the OEM service manual for a detailed component location view.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the keyswitch is in the ON position or when the engine is running.

Conditions for Setting the Fault Codes
This fault code is triggered when the DEF quality sensor detects that the internal temperature has exceeded 125°C.

Action Taken When the Fault Code is Active
The ECM illuminates the amber CHECK ENGINE lamp immediately when the diagnostic runs and fails.
Diesel exhaust fluid injection into the aftertreatment system is disabled.
Engine torque will be reduced.
Conditions for Clearing the Fault Code
To validate the repair, start the engine and let it idle for 1 minute.
The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
The Reset All Faults command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop Talk
Possible causes of this fault code include:

Malfunctioning DEF Quality Sensor

Possible Cause:
1) DEF Fluid failure
2) ECM calibration