Diagnostic Overview
Detroit SPN 3719 FMI 15 typically indicates DPF soot load is above normal at a lower severity level. It is often an early aftertreatment warning that the truck needs a successful regeneration or that the DPF monitoring system needs inspection. Addressing it early can prevent a more severe derate.
Likely Causes
Missed parked regen, short-trip duty cycle, excessive idle time, light-load operation, early DPF restriction, inaccurate pressure sensor, or failed temperature sensor preventing regen.
What To Check First
Review soot load and regen status, allow or perform the proper regen if conditions permit, inspect DPF pressure tubes and temperature sensors, and check for upstream causes of excessive soot. Verify final definition in Detroit DiagnosticLink because FMI meaning can vary by engine year, ACM/MCM calibration, and emissions level.