SPN3216 FMI14 Nox Raw Sensor Does Not Support Self Diagnosis
SPN520355 FMI14 NOx out Sensor Does Not support Self Diagnosis

According to J1939 protocol definition

When the SCU receive the 18FCCF00 01/02/03/04 00 00 00 00 00 00 00 00 command .
The SCU need feedback the self-diagnose result to ECU. This value will be used to assessment the aged states of measurement electrode.