Cummins X15 CM2450 X124B (2018 & Newer) Fault Code: 6766 PID: SPN: 3521 FMI: 18 Aftertreatment 1 Diesel Exhaust Fluid Property- Data Valid But Below Normal Operating Range- Moderately Severe Level

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 aftertreatment diesel exhaust fluid quality sensor is located in the aftertreatment diesel exhaust fluid tank. It may be a combination sensor with the aftertreatement diesel exhaust fluid tank level and tank temperature sensors. Location of the tank and sensor is OEM dependent. Refer to the OEM service manual.

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
The DEF quality sensor has detected that the DEF concentration has fallen below a critical threshold.

Action Taken When the Fault Code is Active
The ECM illuminates the Malfunction Indicator Lamp (MIL) immediately when the diagnostic runs and fails.
Diesel exhaust fluid injection into the aftertreatment system is disabled.
Conditions for Clearing the Fault Code
Start and idle the engine for 15 minutes.
For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where the diagnostic runs and passes.
The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE 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:

Degraded, diluted, or incorrect diesel exhaust fluid
Malfunctioning Aftertreatment DEF Quality Sensor.

Possible Cause:
1) DEF fluid
2) ECM calibration