Cummins X15 CM2450 X124B (2018 & Newer) Fault Code: 3937 PID: SPN: 5848 FMI: 10 Aftertreatment 1 SCR Intermediate NH3 Sensor- Abnormal Rate of Change

Circuit Description
The aftertreatment SCR intermediate NH3 (ammonia) sensor is a smart device that communicates with the engine control module via the J1939 data link. The aftertreatment intermediate NH3 sensor performs its own internal diagnostics and reports malfunctions back to the primary engine control module using the J1939 data link. The aftertreatment intermediate NH3 sensor is used to measure the ammonia in the aftertreatment system.

Component Location
The aftertreatment SCR intermediate NH3 sensor is located in the middle of the aftetreatment SCR catalyst.

Conditions for Running the Diagnostics
This diagnostic runs when the aftertreatment SCR intermediate temperature has been above 170 C [338 F] for a calibratible period of time while the engine is running.

Conditions for Setting the Fault Codes
The aftertreatment SCR intermediate NH3 Sensor reading was not valid.

Action Taken When the Fault Code is Active
The ECM illuminates the amber CHECK ENGINE lamp and/or Malfunction Indicator Lamp (MIL) after the diagnostic fails on two consecutive trips.

Conditions for Clearing the Fault Code
To validate the repair, start and operate the engine to raise exhaust temperatures. This can be done by either driving the vehicle or initiating a stationary regeneration using INSITE™ electronic service tool.
The aftertreatment SCR intermediate temperature must be above 170 C [338 F] for 5 seconds before the aftertreatment SCR intermediate NH3 sensor can run its internal diagnostics.

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.
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 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:

A malfunctioning aftertreatment SCR intermediate NH3 sensor probe
A malfunctioning aftertreatment SCR intermediate NH3 sensor module

Possible Cause:
1) ECM calibration